Special thanks to Robert Fornwalt (yankeebob at dejazzd.com) for his contribution of this reproduction of the Yankee shop manual.




It is recommended that the engine unit be removed from the frame when a major engine repair is necessary as this makes the task of replacing the bearings, cleaning and inspecting the main engine cases, etc., a great deal easier and more efficient. However, the engine can be disassembled while still in the frame leaving only the removal of the stripped main engine cases as a final step.

The sections in Chapter 1 describe, in detail, the correct procedures for the disassembly of the Yankee 500 Z engine. There are just a few points to consider before undertaking any engine repairs, they are: (a) any transmission repair can be completed without disturbing the crankshafts or cylinders, and without removing the engine from the chassis. (b) the removal of the crankshafts necessitates the dismantling of the transmission in order to gain access to the crankshaft coupler. This too may be done without removing the engine. (c) whether the repairs be on the crankshaft or transmission, cleaning, inspection, and heating of the engine cases is much easier when the engine has been removed from the chassis.

Section 1: Removal of the Kickstart Mechanism

1. With a 17 mm wrench loosen and remove the drain plug on the bottom of the engine allowing the oil to flow into a pan capable of holding over 2 quarts of oil. Rock the engine back and forth until all oil has been drained. Check the condition of the drain plug and its gasket. Clean the metal filings from the magnetic part of the plug. Install a new gasket if necessary; then turn the plug into the hole as far as possible by hand. Snug it up against the case with a wrench, then torque it to 20 ft. lbs.

2. If fitted, remove the protective rubber cap on the right end of the selector (gear shift) shaft, and the felt washer beneath the cap. It is not necessary to dismount the kickstart lever in order to remove the kickstart cover unless repairs are going to be made to the kickstart mechanism itself.

3. With a large screwdriver or impact driver, loosen and remove the seven screws that secure the kickstart lever to the engine case. To pull the case loose, push the clutch actuating arm towards the engine and it will force the cover outward. Dont get worried if you see or hear something falling into the case or onto the benchthis is normal and to be expected. Actually either one or both of two things can happen when you pull the kickstarter cover off. First, if the kickstarter idling shaft (LLL-3) stays in the cover when you pull it off, the kickstarter idling gear (MMM-3) will fall loose. Secondly, the kickstart ratchet gear (SSS-3) and retaining rings may fall out when you remove the case. This is the gear on the inside end of the kickstart shaft which is held in place by two split rings (RRR-3) that fit into a groove on the kickstart shaft. The split rings are held in place by a full circle ring (QQQ-3), which is a thin narrow washer. Neither the full circle ring nor the split rings can fall out when the kickstart cover in bolted in place but often do so when the cover is taken off.

4. After removing the kickstart cover be careful not to lose the clutch actuating plunger, (W-2) which is a small cylindrical piece that fits into the clutch actuating mechanism in the cover.

5. If the object of your repair will necessitate removing the transmission, you will need to remove the clutch push rods (Y-2) and balls (Z-2). To do this, tilt the engine toward the right until the exposed push rod begins to slide out of the transmission shaft. Hold your hand under the end of the shaft and catch the rods and balls as they fall out. In all there are three push rods and three balls within the shaft. If any one of them fails to fall out, just leave it in there until you dismantle the clutch.

Section 2: Removal of the Clutch and Primary Driven Gear

1. With a 10mm wrench loosen and remove the bolt that attaches the shift lever to the selector shaft. Remove the lever and the felt washer beneath it.

2. With an impact driver or large screwdriver loosen and remove the five screws that secure the clutch cover. Remove that cover.

3. With a pair of needle nose pliers straighten and remove the five cotter pins from their studs on the clutch assembly.

4.With a spanner type screwdriver remove the five clutch spring nuts (GGG-2) and the five clutch springs.

Note: The spanner screwdriver can be made by cutting a notch in the tip of a large screwdriver. If this is not possible, the nuts can be loosened with needle nose pliers being careful not to damage the slots in the nuts. Use the pliers to loosen the nuts until they are slightly higher than flush with the ends of the studs. A regular screwdriver will then be sufficient to remove the nuts.

5.Remove the clutch pressure plate and all 13 of the clutch plates. If the last clutch plate does not come out with the rest of them use two very small thin screwdrivers to remove the plate by putting the screwdrivers 180 degrees across from each other and lifting the plate out.

6. At this point remove the three clutch push rods and three push rod ball bearings if you have not already done so.

7. Insert Yankee Special Tool No. 1120-411, clutch hub holder, into position on the inner clutch hub. Grasp the clutch hub holder in one hand and with a 19mm socket wrench in the other hand, loosen and remove the clutch nut and lock washer beneath the nut. Remove the clutch hub holder.

8. Remove the inner clutch hub by simply pulling it off the shaft with your hand. Beneath the inner clutch hub there is a large thrust washer; remove that washer. Finally remove the outer clutch hub from its splines by grasping both sides with your fingers and wiggle it back and forth slightly while pulling toward you. Once the hub has been removed you have completely disassembled the entire clutch assembly.

9. Using an impact driver or a large screwdriver, remove the eight screws that affix the primary gear cover (LL-2) to the engine case. This cover is located on the main engine case by two hollow dowel pins between the cover and the engine case. These pins are a very mild press fit into their holes; therefore, the cover will need to be gently tapped away from the cases. The factory has made provisions for this on the cover in the form of two small protrusions cast into the top and the rear of the cover. To remove the cover, tap these protrusions gently with a plastic or rawhide mallet. Alternate between the front and rear protrusions to insure that the cover will come off evenly. Once the cover is clear of the hollow dowel pins (approximately 3/8 inch) it can be removed by pulling it outward with only your hands. Remove the old gasket from either the engine case or the primary gear cover and also remove the two rubber end gaskets (NN-2) if they did not fall out when the case was pulled off.

10.   To remove the primary driven gear (EE-2) just grasp it with your hand and pull it toward you. As you do so, hold your other hand below the end of the transmission main shaft as a few parts may fall from it as the gear is removed.

11.   The primary driven gear rides on two caged needle bearings separated by a spacer approximately 4.5 mm wide. The needles and spacer ride on a steel tube (DD-2) that forms the inner race for the bearings. The outside end of the inner race has a slightly smaller diameter and this small diameter is where the oil seal in the primary driven gear rides. If you have not already done so, remove these parts from the mainshaft. If something appears to be missing, check the inside of the gear as either one of the bearings or the spacer may still be in there. There is also a large flat washer (AA-2) on the mainshaft fitted right up against the transmission mainshaft bearing; remove that washer.

Section 3: Removal of the Transmission

1. Turn the engine so that the right side is facing you. Using two pry bars, or preferably a universal type gear puller, remove the selector spring anchor (X-3) from the selector shaft.

2. The selector spring (W-3) may have been removed with the anchor but if not, remove it now. Next, using a small punch and hammer tap the woodruff keys (RA-3) from their slots in the selector shaft. Most of the later models utilize two woodruff keys, 180 degree apart.

3. Using a pair of external snap ring pliers remove the 14mm snap ring (T-3) and the washer beneath it from the selector shaft.

4. With a small hammer and chisel bend the folded parts of the countershaft sprocket lock washer (CCC-3) away from the sprocket nut. Once you have succeeded in prying it away from the nut somewhat trade the chisel for a flat-ended punch or drift and flatten the tab of the washer up against the face of the sprocket.

5. Locate Yankee Special Tool No. 1120-551, countershaft sprocket holder, and position it on the sprocket. With a inch drive ratchet and 26mm socket loosen and remove the countershaft sprocket nut (DDD-3) by turning it clockwise (left hand thread). Remove the tab washer and sprocket by pulling them outward off the countershaft.

6. Turn the engine so that the left side is facing you. Grasp the left end of the selector shaft with your hand and pull it directly toward you. If necessary, tap it lightly on its right end with a plastic or other soft faced mallet to start it moving; then pull the shaft completely out of the engine case.

7. With a large screwdriver or impact driver remove the seven screws which mouth the transmission support plate (A-3) to the engine case.

8. Turn the engine up-side down. Remove the six screws that fasten the transmission inspection cover (KKK-3) to the engine case; remove the cover and its gasket to expose the shift detent housing (BB-3) which is a large slotted screw located in a recessed hole at the side of the opening. With a large screwdriver remove the detent screw and the fiber gasket beneath it. With a pair of needle nose pliers remove the detent spring and plunger that are located under the screw. If no such pliers are available you will need to turn the engine right-side up and catch these two pieces as they drop out.

9. With the engine preferably up-side down, tap on the right end of the countershaft to start the whole transmission gear cluster and support plate moving toward the left.

NOTE: The reason for keeping the engine up-side-down is to allow you to watch through the inspection hole as the transmission is removed so you can determine whether or not all the components are being taken out together as a unit. This is especially important if you are working on your first Yankee transmission. Its a lot easier to figure out a gearbox that has been removed intact rather than trying to piece together something that you never saw properly assembled.

10.   Continue pushing on the right end of the countershaft until it is flush with the engine case; at the at point grasp the left end of the mainshaft with one hand, the support plate with the other, and carefully withdraw the transmission unit form the engine case.

11.   Before you set the transmission assembly down on the bench, check the bearings and mounting bosses inside the transmission cavity for any shims or washers that might have stayed there and replace them, if any, on their respective shaft or shift drum. Also check the interior of the engine cavity very closely for any shims that may have fallen loose. If you find a shim and dont know where it belongs, dont be alarmed. Just set it aside until later because the transmission repair section of this manual will show you where everything belongs.

Section 4: Removal of Jackshaft

1. On the right side of the engine, just to the front of the kickstart area, there is a ball bearing through which the primary drive jackshaft (A-2) passes. With a small hammer and chisel, bend the lock tab washer (K-2) securing the nut on the end of the jackshaft up. When the lock tab has been flattened, loosen and remove the nut (L-2 which has left hand threads) with a 26mm socket.

2. If the nut is tight, you will need to prevent the crankshaft and jackshaft from turning. Using flywheel holding tool No. 1120-121, hold either magneto flywheel from turning and at the same time turn the jackshaft nut clockwise to remove the nut and lock washer.

3. With a plastic or rubber mallet tap the end of the jackshaft lightly, moving it to the left. While doing this, place your other hand inside the transmission cavity beneath the jackshaft sprocket. When the shaft has moved about inch to the left the two jackshaft sprocket half-ring retainers (D-2) may fall from the shaft. If they dont, lift them off the shaft with your fingers then continue moving the shaft toward the left until it is completely removed from both of its bearings.

4. Remove the jackshaft sprocket from the primary chain. Check the inner race of the right side jackshaft bearing for any shims (G-2) that may have been between the sprocket and bearing. Not all Yankee Z engines are fitted with these shims, but some are.

Section 5: Removal of the Magnetos

1. With a large screwdriver or impact driver remove the three screws that anchor the right magneto cover to the engine and remove the cover.

2. Locate Yankee Special Tool No. 1120-121, magneto flywheel holder, and insert the two prongs of the holder into the holes in the magneto flywheel. With a 26mm six point socket and a breaker bar or a ratchet remove the flywheel nut (XX-1) and its lock washer. Upon removal of this nut you will see that it is actually a bolt with a short peg on its threaded end.

3. You will now need Yankee Special Tool No. 1120-131, magneto flywheel puller. This puller comes with two separate pieces, the first being a small threaded adapter which screws into the end of the crankshaft and gives the second part, the puller itself, something to push against.

4. Turn the threaded adapter into the crankshaft, screwing it in until the shouldered part of the adapter touches the end of the crankshaft. Screw the puller into the threads provided in the magneto flywheel. It is important that the center bolt of the puller be backed out far enough to allow the puller to be screwed in all the way, which is approximately 5 to 6 turns. Failure to do this can result in the threads being destroyed on the puller or the flywheel or both.

5. Now using a 19mm wrench or socket turn the center bolt of the puller clockwise while holding the flywheel with the special tool. Continue to turn the bolt until the flywheel is popped loose from the crankshaft. After the flywheel has been freed, remove it from the stator by pulling it directly towards you with your hands. Remove the puller from the flywheel and unscrew the adapter from the end of the crank.

6. With a small sharp chisel and a hammer, make a line across the edge of the magneto stator plate and one of its mounting bosses. This mark will be used as a timing reference when reassembling the engine, however do not rely on this mark for the final timing. It is only a starting point to be used when you re-time the engine.

7. Remove the three screws that mount the stator to the engine and lift the stator off its mounting bosses. Using a hammer and small chisel or punch, gently tap the woodruff key (G-1) on the crankshaft until it is out of the key slot. Check the key for damage and wear and if it shows signs of either, discard it. If you keep the key, find a point on the magneto flywheel where the magnetism is strong and store the key there.

NOTE: If you are not going to replace the magneto assembly or the main bearing and seal, it is not necessary to remove the stator and its wires from the outer engine cover. Threading the wires back through the hole in the cover is sometimes a bit difficult and unnecessary if the mag assembly is not to be replaced. Instead, simply leave the stator attached to its mounting bosses on the outer crankcase half.

8. You will also notice that the end of the crankshaft is hollow. The reason for this is explained in the crankshaft removal section of this manual. However there is a small O-ring (VV-1) located inside the ends of the crankshaft just at the base of the threads. This O-ring fits over the peg on the end of the flywheel bolt. If the O-ring did not come off the flywheel bolt you will need to remove it by using a small thin screwdriver or a piece of safety wire bent with a small hook on the end. Just reach inside the end of the crankshaft with the tool, catch it in back of the O-ring and pull the O-ring out. The O-ring should be replaced every time the flywheel bolt is removed.

9. Remove the left magneto assembly in exactly the same manner as the right magneto.

Section 6: Removal of the cylinders and pistons

1. To completely disassemble the Yankee engine it is necessary to rotate many parts on the drive train and crankshaft in order to remove them from the engine. This rotation results in up and down movement of the pistons and connecting rods. If the cylinders and pistons were removed while these parts were being rotated the connecting rods would be free to flop and bang around in the engine cases, possibly causing damage to either the rods or cases. Therefore, when doing a complete engine rebuild or any crankshaft work we recommend that the previous disassembly steps be carried out before removing the top end components.

2. Remove both carburetors if you have not already done so.

3. The sequence and procedure for loosening the cylinder head nuts is fairly important, therefore follow the instructions carefully.

(I.   Diagram needed to show sequence)

4. First using a 12mm socket, loosen each of the cylinder head nuts turn using the sequence shown in fig.1. It does not matter which head is loosened first just as long as the proper sequence is followed on each head and that the nuts are loosened only turn each. When each nut has been loosened turn repeat the process and loosen all of them another turn using the same sequence. If the heads have been torqued properly, the nuts will become very loose during the second turn. Remove all of the head nuts and flat washers.

NOTE: If you do not follow this procedure it is possible under certain circumstances to distort the cylinder heads.

5. Remove both the heads and set them aside. If you do not see the head gaskets lying on top of the cylinder liners, turn the heads upside-down and pry the gaskets loose from the heads with your fingernails or a small screwdriver.

NOTE: If the compression releases are still installed in both heads and are connected by the cables, merely handle the heads as a unit, removing both of them from the cylinders simultaneously.

6. If the cylinders have a balance tube located between the intake manifolds, remove the tube.

7. Grasp either cylinder with both hands and lift it upward slowly until the piston is freed and the cylinder is clear of the mounting studs. Repeat this procedure with the other cylinder. Wrap a clean shop rag around each connecting rod so that each crankcase opening is entirely covered. This is to prevent the wristpin clips from falling into the crankcase while you are removing them.

8. Remove the cylinder base gaskets if they are still stuck onto the crankcases. If they are not, then remove them from the bases of the cylinders and discard them.

9. With a pair of needle nose pliers remove the wristpin clips (D-1) from both sides of both pistons and discard the clips.

10.   Butt the Yankee Wristpin Drift Tool No. 1120-211 against the outside end of either wristpin. Push the wristpin towards the center of the engine while supporting the piston from behind with your other hand. Continue inward with the drift until the wristpin is entirely clear of the wristpin bearing and the piston can be lifted off the connecting rod.

NOTE: Do not attempt to remove the wristpin by hitting the drift with a mallet or without supporting the piston from behind. Under normal operating conditions the connecting rod does not receive any side loads; therefore, it is not designed to withstand such loads. Even gentle tapping against the wristpin drift with a mallet or unsupported side thrust on the piston could bend the rod or mar the bearing. If the wristpin is tight and will not move, remove the drift and push the pin out with Yankee Wristpin Tool No. 1120-221. It is not necessary to completely remove the wristpin from the piston, simply push it through far enough to remove the piston assembly from the connecting rod.

11.   Repeat this procedure for the other piston assembly. If these pistons are to be reused, mark them with L and R accordingly. Remove the wristpin needle bearings (B-1) from the small end of the connecting rods and place them on their respective wristpins.

Section 7: Removing the crankshafts and primary chain

1. Loosen and remove the seven screws that hold the left outer crankcase to the main engine case. Grasp the outer case by its two cylinder studs and in back of the case at the bottom. Wiggle the case slightly while pulling outward.

When the case comes loose, slide it outward off the end of the crankshaft. Before setting the case down, check the end of the crank and the inner race of the main bearing for shims. Repeat this removal process for the right outer crankcase.


SEPECIAL NOTE: Before proceeding further you must understand how these crankshafts are connected to one another. The inside end of each crankshaft is tapered, very similar to the outside ends, but slightly shorter. The inside flywheels of both crankshafts are marked with either an L or and R. This tells you that the threads on the inside ends of that flywheel are either left or right hand threads. Note, they may also be marked with an I or a D instead of the L or R. The I means Izquierda, Spanish for Left and the D means Derecha, Spanish for Right. Remember, I means Left; D means Right. These tapered ends fit into a crankshaft coupler, which is also the engine sprocket and has two matching tapers inside it. The cranks are held together with a coupler bolt, which looks like a stud except that one half of the stud has right hand threads and the other half has left hand threads. When this stud is installed between two crankshafts (one with right hand threads, the other with left hand threads) and turned in one direction it draws that crankshafts together; turn it in the other direction, it pushes them apart. Therefore, to remove the crankshafts from the engine you must first separate them from one another. To do this the coupler bolt is turned in the proper direction. Access to the coupler bolt is through the outer ends of the crankshaft main bearing journals, which are hollow. A long hardened Allen wrench can be inserted through the hollow end of the crank into an Allen socket in either end of the coupler bolt. When enough torque has been exerted to the coupler bolt one, and only one, of the crankshafts will be popped loose from the taper. It is impossible to predict which one will come loose first as this depends on which crankshaft has the poorest fit into the coupler.

Turning the coupler bolt in the same direction 8 or 10 turns will allow one crankshaft to be extracted completely but it will also present another problem. That problem is: How do you get the second crankshaft out? If the coupler bolt is designed to exert pressure between the two cranks and you remove one of the cranks, then there is nothing left on one side for the coupler bolt to push against. Consequently a special tool must be used to provide a buttress that can be pushed against to remove the second crankshaft. With this explanation in mind, proceed now to the detailed instructions for the removal of the crankshafts.

2. You will now need several special tools to remove the crankshafts. They are No. 1120-331, crankshaft coupling holder; No. 1120-335, crankshaft coupling holder bar; No. 1120-301, crankshaft removal tools (a 3-piece set); and two of No. 1120-341, crankshaft extractor Allen wrenches.

3. First rotate the crankshafts 360 degree or until you locate a letter stamped on the outside edge of the inner flywheels. There should be an L stamped on the inside flywheel of the left crankshaft and an R on the inside flywheel of the right crankshaft. If the letters are reversed (L on inside flywheel of right crank, R on inside flywheel of left crank) make a mental note of this condition, which means that the crankshaft assembly has been installed backwards. This does not affect the engines performance or longevity, but you will need to remember this information when performing the actual task of removing the crankshafts. Now turn the crankshafts so that the connecting rods are located near top dead center.

4. Install the crankshaft, coupling holder. This is done by lifting up the top run of the primary chain and slipping the hooked end of the tool over the teeth of the crankshaft coupler with the primary chain running around the entire tool. Hold the tool in place and rotate the crankshaft slightly until you feel the tool drop into place on the teeth of the coupler.

5. At that point move the tool until the large hole at the rear of the tool is aligned with the two jackshaft bearings. Insert the crankshaft coupling holder bar through the left jackshaft bearing passing it through the end of the coupler holding tool and finally into the right jackshaft bearing. Be sure that the bar has entered the right bearing completely. The crankshaft is now locked in place and cannot turn.

6. With the crankshaft holding tools in place it is now necessary to heat the engine sprocket with a propane torch. The heat serves to soften the large amount of hardened Loctite, which is present on the threads of the coupler bolt and inner flywheels. It also helps the cranks to break loose from the tapers. Do not attempt to remove the crankshafts without using heat. This rise in temperature is necessary; otherwise the amount of torque that will be required to loosen the coupler bolt could possibly be enough to break the extractor tool or round out the hex end of the coupler bolt.

7. When the temperature of the engine sprocket reaches approximately 200 degrees (or when the oil on the sprocket becomes hot enough to emit smoke) insert one extractor wrench into the right end of the crank assembly pushing it inward until the 8mm Allen key is fully installed in the Allen hex that is machined into the right end of the coupler bolt. Repeat this procedure with the second extractor wrench installing it through the left end of the crankshaft assembly. Tap the ends of both extractor wrenches lightly with a plastic or brass mallet to be sure that they are fully inserted into their Allen sockets.

8. Install a 19mm long handled box end wrench on each extractor wrench, with both box end wrenches pointing directly upward and as close to parallel with one another as possible. Then turn both wrenches forward simultaneously, using equal pressure on both.

NOTE: The box end wrenches are turned forward (counter clockwise when looking at the engine from the leftclockwise when viewing it from the right) IF the crankshafts have been installed in the engine properly. If you detected that the crankshaft assembly was installed backwards as noted in Paragraph 3 of this section, the wrenches must be turned in the opposite direction (clockwise when viewed from the leftcounter clockwise when viewed from the right).

9. It should require approximately 60 to 70 ft. pounds of torque to pop the first crankshaft loose from the tapers. If you exceed this amount, you may break the extractor wrenches; therefore if it appears that excessive torque is necessary to break the crankshaft loose from the tapers, reheat the engine sprocket and try turning the extractor wrenches again.

10.   There is no way of predicting which crankshaft will come loose firstit all depends upon the fit of each crank into the tapers of the engine sprocket. When one does break loose continue turning the coupler bolt, which will cause the loose crank to move outward until it can be slid free of its main bearings by hand.

11.   After one crankshaft has been extracted remove the coupler bolt from the inside of the engine sprocket if it did not come out with the crankshaft that was just removed.

12.   You will now need the remainder of the crankshaft extracting tools to remove the other crank. As explained earlier, when the coupler bolt is turned it pushes between the two crankshafts forcing one of them to come loose. After the first crankshaft is removed something must be installed on that end of the engine sprocket so that there will be something to push against in order to remove the other crank.

13.   Therefore, Yankee Special Tool No.1120-301 is now needed to remove the remaining crankshaft. Actually this tool is three separate pieces. First there is a heavy steel backup plate, which slides over the 1st row of teeth on the engine sprocket and blocks off the hole in the sprocket where the now-removed crankshaft was. The other two parts are threaded bolts with an Allen hex socket on either end; one of these bolts has left hand threads, the other has right hand threads.

14.   If the crankshaft stamped L (or I) is still remaining in the engine, then you will need to utilize the Allen bolt that has left hand threads. If the crank is marked R (or D) then the right hand threaded Allen bolt must be used. Whichever it is, screw the appropriate bolt into the inside end of the crankshaft by inserting it through the main bearing of the removal crankshaft and turning it in as far as it will go or until the head of the bolt is flush with the end of the engine sprocket.

15.   Now install the steel backup plate on the engine sprocket. To do this, slide the tool down over the first row of teeth on the end of the sprocket that has had the crankshaft removed. You may find it necessary to slide the crankshaft, coupling holder over a bit to allow the open edge of the backup plate to slide down between the sprocket teeth. Also the whole remaining crankshaft assembly may have to be moved as far as possible to one side in order to allow the backup tool to pass between the end of the engine sprocket and the engine case.

16.   Utilizing just one of the extractor Allen wrenches, slide the wrench through the end of the remaining crankshaft and into the Allen hex socket in that end of the bolt. If the crankshafts were installed properly, turn the bolt forward (clockwise, looking from the right side, counter-clockwise from the left) using the 19mm box end wrench. As before, if the crankshafts were installed backwards you will need to turn the wrench in the other direction.

17.   60 to 70 ft. pounds of torque may be required to break the crankshaft loose from the engine sprocket. If that amount of force is exceeded the extractor wrench may break or the Allen socket in the coupler bolt may become rounded. If necessary, reheat the engine sprocket by playing the flame of a propane torch over the special tools that at this point will have covered the sprocket.

18.   The crankshaft will probably break loose with a loud snap. At that point continue to turn the tool until the crank can be removed by lifting it out of its main bearing.

19.   Remove the coupling holder bar from the jackshaft bearings and remove the crankshaft coupling holder. Then remove the primary chain, engine sprocket, and the remaining special tools. The job of crankshaft removal is now complete.

Section 8: Removal of the bearings

1. The Yankee engine, like many aluminum motorcycle engines, requires the use of heat to accomplish the removal and replacement of the main bearings and transmission bearings. In all there are 10 ball bearings in the Yankee engine.

2. Five bearings are No. 6304 ball bearings. They are: all four of the transmission bearings and the right jackshaft bearings

3. Three of the engine bearings are No. 6205 ball bearings. They are the outside crankshaft main bearings and the left jackshaft bearing.

4. Three of the engine bearings are No. 6205-C3 ball bearings. These are the inside crankshaft main bearings. They are similar to the other three 6205 bearings except that the C3 units have a little extra clearance between the balls and the races. They need this clearance because they are closest to the primary drive and that means that they will run a little hotter because of the extra loading at these parts of the crankshaft. Always use the 6205-C3 for both inside main bearings on the 500 Z engine.

5. Thoroughly clean all of the engine cases with a good solvent and blow them dry with compressed air. Heat the main engine case in an oven until the case temperature reaches 250 to 300 degrees F. (This takes about 25 minutes in an oven set at 475 degrees). At that point the bearings can be easily removed by gently pushing them out of their mounts. The inner main bearings as well as the left jackshaft bearing will be removed intact with the steel sleeve in which they are encased. The two right transmission bearings do not have this steel bushing.

NOTE: Enough emphasis cannot be placed on the importance of using only heat when removing or replacing bearings in the Yankee engine. Do not hammer or press the bearings in or out of the aluminum; otherwise the mounting holes will become scored, enlarged, or distorted. If an oven is not available, a heating torch may be used providing the entire engine case is heated evenly. Because of the size and mass of the case this can be a bit difficult; but this difficulty does not seem so great once the very expensive price of a new case is learned.

6. The two inner main bearings should be removed using Yankee Special Tool No. 1120-335. This tool was designed to fit through the two jackshaft bearings and through the crankshaft coupler holding tool. It also makes an effective tool for removing the two inner main bearings. You will need to use a large washer (2-1/8 in. O.D., 8/10 in. I.D.) or an old 6304 ball bearing in conjunction with the tool.

Before heating the cases, slide the special tool through one of the main bearings, install the large washer on the end of the tool inside the engine case, and slide the tool all the way in until the large washer seats against the opposing main bearing sleeve.

Now, heat the engine case as described above, with the special tools in place. When the proper temperature has been reached, tap lightly on the end of the special tool and one of the main bearings seals and sleeves will fall out. Using the same special tool, (which is now very hot) remove the other main bearing and sleeve.

This procedure is recommended, as it is important that the inner main bearing sleeves be removed evenly, without cocking them sideways. If they are cocked sideways in the case, you stand the chance of damaging the aluminum sealing surface of the main engine case. The rest of the bearings in the main engine case can be removed (while the case is hot) with a suitable drift. They may even fall out. Once the main bearing sleeves have been removed, the bearings can be pressed from the sleeves.

7. The outer main bearings, as well as the two ball bearings in the transmission backing plate (A-3) can be removed following the procedure described above. Remember, you must remove the Magneto stators from the outer crankcase halves before you heat them, as the stators and wires would be damaged by the heat. The outer crankcase halves must remain in the 475 degrees oven for about 10 minutes, and the transmission backing plate for about 8 minutes before the bearings can be removed. It is easier to remove the outer main bearings from the crankcase halves if you first remove the crank seals. Simply pry them out with a screwdriver, being careful not to score or scratch the aluminum where the seal is seated in the crankcase half. This competes the disassembly of the Yankee 500 Z engine.



Section 1: Repair of the Kickstart Mechanism

1. Remove the kickstart lever from its shaft if you have not already done so.

2. Slide the kickstart idler shaft (LLL-3) from its bronze bushing in the kickstart cover if the shaft did not remain in the main engine case.

3. Remove the full circle ring and split retaining rings from the kickstart shaft, and pull the ratchet gear from the shaft.

4. Securely clamp the first inch of the splined end of the kickstart shaft in a soft-jawed vise as shown in Fig.___. Rotate the entire kickstart cover in a counter-clockwise direction. As you do so, the kickstart ratchet (TTT-3) and its positioning fork (UUU-3) will slide up on the kickstart shaft. Remove the ratchet and fork when they are clear of the retaining pin (VVV-3) and hold the cover against the spring tension.

5. Continue to rotate the cover in the same direction until the kickstart return spring is wound tightly enough to clear the kickstart stop, which is cast into the bottom of the case.

NOTE: there are flat spots in the spring retaining washers, which also must be positioned so as to clear the kickstart stop.

6. When the washers are in the proper position and the spring is wound tight enough to clear the stop, press the entire case downward as far as it will go, thereby forcing the kickstart shaft, spring, and retaining washers upward and past the kickstart stop. Slowly release the spring tension by letting the cover move clockwise.

7. Remove the kickstart cover and shaft from the vise, and by holding the cover in your hands and pressing the splined end of the shaft against the workbench, push the kickstart shaft through the case as far as it will go. The end of the kickstart spring will slip off of its retaining pin, and the shaft, spring and retaining washers can now be removed from the kickstart cover.

NOTE: There are thrust washers on both sides of the spring retaining washer snap rings. If either of these thrust washers is damaged or worn, it should be replaced.

8. If you are going to replace the kickstart return spring, it will be necessary to remove the 18mm snap rings (XXX-3), which hold the spring retaining washers in place. The old snap rings should not be re-used. NOTE: There is a right way and a wrong way to install a snap ring. This is true not just on the kickstart shaft, but for a part of any piece of machinery that utilizes snap rings, both internal and external. A snap ring is manufactured by stamping it out of an appropriately thick piece of steel. Because it is stamped, one side of the ring will have a sharp edge and the other side will have a slightly rounded edge. If you rub your thumb or forefinger across both edges of the snap ring, you will feel the difference in these edges (Fig. ____). Snap rings fit into grooves, which are machined with square corners inside them. When a snap ring is in its groove, it is usually capable of withstanding a greater side load in one direction without breaking or popping out, than it is in the other direction. This is because when the snap ring has its rounded edge forced against the side of the groove, the roundness tends to open it up, which can then allow it to be pushed out of the groove. On the other hand, when the ring is pushed in the other direction, it seats its square edge against the square edge of the groove, and is less likely to be dislodged. For this reason, a snap ring should always be mounted with its square edge facing in the direction that the ring will be thrust under load. An easy way to remember this is to imagine in what direction a snap ring will move if it comes out of the groove. Then, when mounting the ring, always put the square edge facing in that direction. Both snap rings on the kickstart shaft should be installed with the sharp edge facing the splined end of the shaft.

9. To properly reassemble the kickstart mechanism, you will need Yankee special tool No. 1120-545, O-ring protector. Discard the old O-ring in the kickstart cover (BBBB-3) and install a new one. Slide the center shaft of the O-ring protector through its outer shell and install the tool in the kickstart cover. Be certain that the protector is fully seated in the cover.

10.   Holding the O-ring protector in one hand and the kickstart cover in the other, clamp the knurled end of the O-ring protector in a vise as shown in Figure ______.

11.   Slide the kickstart shaft in place (the shaft should be pre-assembled with the return spring, thrust washers, circlips, etc.) pushing the center rod of the O-ring protector out with the splined end of the kickstart shaft.

NOTE: the return spring coil should point counterclockwise while looking down on it.

12.   Continue to press down on the kickstart shaft with your thumbs, and at the same time pull the case upward, toward you with your fingers. The splined end of the shaft will slide part way into the O-ring protector and the case will be pulled up and over the splines.

13.   Remove the O-ring protector and again clamp the splined end of the shaft in a soft-jawed vise. By repeating the process used for disassembly, it will be possible to reassemble the kickstart mechanism. Dont attempt to place end of kickstart spring over its retaining pin until the spring and washers are past the kickstart stop. Simply let the end of the spring butt against the idler shaft bushing boss. See Fig. _____. Be certain to turn the case only in a counterclockwise direction. Turning the case only a small amount in the wrong direction will break the kickstart return spring.

14.   There is a groove ground in the splined end of the kickstart shaft, which allows the kickstart lever pinch bolt to pass through. This groove must be at the bottom of the case after the kickstart mechanism is assembled. (Fig. ______).

15.   When the looped end of the kickstart return spring is in place over its retaining pin, rotate the case counterclockwise of a turn or more until the groove in the shaft is towards the bottom of the case. The spring must be wound at least of a turn but not more that two turns.

16.   With the groove now at the bottom, and the spring wound the required amount, slide the kickstart ratchet (with the positioning fork removed) in place over the spiraled cam slots on the kickstart shaft. The kickstart stop on the ratchet should come in contact with the stop in the case, and hold the case in position against the spring tension. If it does not, remove the ratchet, rotate it 90 degrees (until another slot lines up) and again slide the ratchet down the spiraled slots. Repeat this process until the ratchet will hold the case and kickstart shaft is in the proper position. Now again remove the ratchet, replace the positioning fork on the ratchet, and replace the ratchet on the shaft, again holding the shaft and case in the proper relationship.

17.   Reinstall the kickstart lever, ratchet gear and its retaining rings, holding the rings in place with a dab of grease.


Section 2: Repair and Assembly of the Clutch

1. The Yankee 500 Z clutch is a multi-plate dry clutch. There are 6 fiber driving plates, 6 thin steel driven plates, and 1 thick steel driven plate. As with any clutch of this type, the condition of the surface of the clutch plates is very critical for proper operation.

2. Thoroughly clean and inspect the clutch basket (RR-2) for signs of cracking and excessive wear. If you detect any signs of cracking or if indentations are beginning to form along the slots of the clutch basket, it should be replaced.

3. Install the clutch basket over the splines of the primary driven gear.

4. Slide the clutch hub thrust washer (SS-2) (flat side toward clutch basket; beveled side out) over the mainshaft and up against the clutch basket.

5. Clean and inspect the inner clutch hub (TT-2). If any of the splines on the hub are damaged or if one or more of the studs are loose, the hub should be replaced.

6. Slide the clutch hub over the splines on the end of the mainshaft and up against the thrust washer.

7. Install a 12mm lock-washer over the mainshaft and, using Loctite on the threads, install the clutch nut (VV-2).

8. Select Yankee Special Tool No. 1120-411, clutch hub holder, and place it over the clutch hub. Using a 19mm socket and torque wrench, tighten the clutch nut to 45 ft. lbs. or torque.

9. Clean and inspect all 13 clutch plates. It is imperative that all traces of dirt and oil be removed from the plates. Any amount of oil film present on the plates will cause them to slip and eventually destroy the clutch. The steel plates should be cleaned in a solvent, which leaves no residue. The fiber plates should be wire-brushed to remove any glazing, which may be present. Place each plate on a flat surface such as a piece of glass, to check for warpage. If any one of the plates appears to be bent, it should be replaced. If the friction material on any of the fiber plates is excessively worn (nearly flush with the steel part of the plate) those plates should also be replaced.

10.   Fit the thick steel plate over the inner clutch hub. The, alternate one fiber plate with one thin steel plate. The last one installed will be a steel driven plate.

11.   Clean and inspect the clutch pressure plate (ZZ-2). Check for signs of excessive wear on the friction surface. Also, check to see that the clutch throw-out bearing turns freely. You should be able to turn it with pressure from your finger. If you cannot turn the bearing, remove the snap ring (DDD-2) and thrust plate (CCC-2). Clean and re-grease or replace the bearings, reinstall the thrust plate and install a new snap ring with the sharp edge facing outward.

12.   The clutch pressure plate is operated by three identical pushrods and three ball bearings, which are located in the center of the hollow main shaft. If the kickstart mechanism is already in place, it is necessary to install these pushrods and bearings now. Clean and inspect the pushrods, and replace any that are bent or badly worn.

13.   Partially fill the center of the mainshaft with a high temperature grease, and insert one of the pushrods. Now, insert 2 of the ball bearings, a second pushrod, the remaining ball bearing and finally the third pushrod. It really doesnt matter whether you put the two ball bearings in before the 2nd pushrod or after it, but you must have a total of three pushrods and three bearings with at least one bearing between each pushrod.

14.   Install the pressure plate over the five studs of the inner clutch hub.

15.   Measure the free (un-compressed) length of each of the five clutch springs. If any one of them measures less than 1.50 inches, it should be replaced.

16.   Put the springs into their cups in the pressure plate, and fit the slotted clutch spring nuts to the studs.

17.   Turn each nut inward until a slot in the nut can be aligned with the hole in the stud. Do not yet install the cotter pins.

18.   It is now necessary to check the clutch for proper operation and adjust if necessary.

19.   Select Yankee Special Tool No. 1120-401, clutch operating tool, and fit it to the clutch actuating arm on the right side of the engine. (If the kickstart mechanism is not in place, it will be necessary to temporarily install it.) With one hand, move the tool to the left far enough to disengage the clutch pressure plate. With the other hand, operate the kickstarter, which will cause the pressure plate to turn. If the clutch springs are not adjusted evenly, the pressure plate will not run true, but will seem to wobble while turning.

20.   To correct this, turn the kickstarter slowly, and locate the high point of the pressure plate (where it is farthest away from the rest of the clutch plates). Release the clutch, and turn the slotted clutch spring nut, or nuts, nearest the high point inward (tighten) one-half turn, and repeat the test. Continue this procedure until the pressure plate runs true. When the clutch is properly adjusted, the pressure plate will move outward in a plane parallel to the rest of the clutch plates.

21.   When the clutch nuts have been properly adjusted, install a cotter pin (Yankee Part No. 1102-355) through the hole in each stud, and bend the legs of the pin outward. If safety wire is used instead of cotter pins, thread one length of wire through all 5 studs, and twist the ends together with 4 or 5 revolutions. If the wire is pulled too tight, it will break during operation, so leave a small amount of slack in the wire. Bend the twisted ends downward against the pressure plate.


Section 3: Repair and Assembly of the Transmission

A.   Operation of the Transmission

1. The two geared shafts in the transmission are the MAINSHAFT (Fig. _______) and the COUNTERSHAFT (Fig. ______). Power is delivered to the gearbox through the clutch, which is fitted to the left end of the mainshaft (left as one sits on the motorcycle). There are five gears on the mainshaft, one of which is a gear cluster comprising 5th and 6th gears. Two of these gears, 3rd and 4th, are freewheeling or idling gears (spin freely on the mainshaft) while the others, including the 5th and 6th gear cluster are splined to the mainshaft. Power is transmitted from the mainshaft to the idling gears through the use of ENGAGING DOGS, which are present on the inboard sides of both 3rd and 4th gears, and on both sides of the 5th/6th gear cluster. The 5th/6th gear cluster slides to the right to engage 3rd gear and to the left to engage 4th. 1st and 2nd gears on the mainshaft are splined to the shaft but do not slide from side to side as does the 5th/6th gear cluster.

2. Power is transmitted from the mainshaft through the gears and to the COUNTERSHAFT. There are six gears on the countershaft. Two of these gears are splined to the shaft, 3rd and 4th, while the other four are idling gears. Again, power is transmitted from the idling gears to the countershaft through the use of engaging dogs which are present on both sides of the splined gears and one side only of the idling gears. 3rd gear (splined to the countershaft) slides to the right to engage 2nd gear and to the left to engage 6th gear. 4th gear (splined to the countershaft) slides to the left to engage 1st gear and to the right to engage 5th gear.

3. The sliding gears of both shafts are moved back and forth by SHIFTING FORKS (Fig. _____). There are three of these in the Yankee transmission, and all three are identical. These shifting forks fit into machined grooves on the sliding gears. The sliding gears spin freely in the shifting forks but are held in lateral position by the forks.

4. The shifting forks slide back and forth on, and are actuated by, the SHIFTING DRUM (Fig. ____). The forks are held in position by small, hardened steel pins (Fig. _______), which fit through holes in the fork and into grooves in the shift drum. These grooves are machined in a manner such that when the drum is rotated, the forks are moved side to side by the hardened pins. This moves the sliding gears from side to side, engaging the correct idling gears. NOTE, the shifting fork pins are available with 0.1mm, 0.2mm and 0.5mm offset both right and left, as well as with no offset. By using pins with different amounts of offset, it is possible to obtain nearly perfect gear engagement in every gear.

5. The shifting drum has eight depressions or dimples machined into the outer circumference of its right end. These dimples are called detent holes. When the transmission is in any one gear, or either neutral (there are two neutrals, therefore two neutral detent holes), a spring-loaded plunger fits into one of these holes. This plunger holds the drum in position so that vibration and other forces cannot jar the transmission out of gear. It also prevents the drum from going past a gear, and actually helps to pull the drum in place to engage a gear. The spring loaded device which holds the transmission in gear is called the DETENT ASSEMBLY and is composed of a large headed hollow screw, a plunger, a spring and a fiber sealing washer. The detent is located in the bottom of the main engine case, under the transmission inspection cover.

6. The shifting drum has five round pegs protruding from its left end. These pegs are called the SELECTOR PINS and are the means by which the shift drum is rotated. The pins are engaged by the spring loaded SELECTOR PAWL (Fig. ______) on the selector shaft to which the gearshift lever is attached. There is also a SELECTOR SHAFT RETURN SPRING located over the right side of the selector shaft and outside of the main engine case. The function of this spring is to return the selector mechanism to a neutral position after one gear is engaged so that the next gear can be engaged. Adjustments to the position of the spring are made by turning the eccentric anchor pin located adjacent to the spring.

7. When the selector shaft is rotated by moving the gearshift lever, the selector pawl engages one of the selector pins on the shift drum, and turns the drum to the next gear position. When the gearshift lever is released, the selector return spring pulls the selector shaft back to its original position. As this happens, the selector pawl being spring loaded snaps back over the top of the next selector pin and is ready for the next gear change. The selector shaft assembly is designed so that the shift drum can be rotated only far enough to engage the next closest gear with one movement of the lever. Two exceptions are both neutrals as they lie HALFWAY between the next lowest and next highest gear. This obviously is necessary so that the transmission can be shifted from 1st gear to 2nd and from 2nd to 3rd without stopping at the neutrals in between.

8. The transmission of motion from your foot, through the selector mechanism and into the transmission is as follows. The shift lever is depressed (or pulled up), rotating the selector shaft against the pressure of the selector return spring. As the shaft is rotated, the selector pawl turns with it, engaging a selector pin on the end of the shifting drum, rotating the drum. As the drum rotates, the shifting fork pins are moved from side to side by the grooves in the drum. Naturally, the shifting forks and the gears at the ends of the forks must also move from side to side. The engaging dogs of one of the sliding gears come in contact with the engaging dogs of one of the idling gears, thereby causing the idling gear to turn with the shaft.

When you release the shift lever with your foot, the selector spring pulls it back to its original position. As this happens, the selector pawl also returns to the center position, sliding over the end of the next selector pin in the shift drum ready to engage that pin for the next gear change.


Section 3: Repair and Assembly of the Transmission

B.   Checking the Gearbox Components for Wear

1. Before reassembling the transmission it is necessary to thoroughly inspect each component for signs of damage or excessive wear. Any part that has a thrust or friction surface showing a blue color should be replaced, as this indicates the part has been subjected to excessive heat.

2. Carefully check the teeth on all the gears for excessive wear or damage. If you find such damage on one gear, be particularly careful about inspecting its opposing gear on the other shaft, as it may be damaged also.

3. The engaging dogs on all of the gears should be inspected. If any of these dogs have excessively rounded edges, they should be replaced. This could cause two engaging gears to reject each other, or miss a shift. Also, be sure that the sliding gears are free to slide back and forth on their shafts.

4. If the transmission is being repaired because of broken gear teeth, a foreign object in the gearbox, or some other breakage, which resulted in sudden stoppage of the gearbox and drive train, the mainshaft and countershaft should be checked for straightness. They may have been bent due to high loading forces created when such things occur. Place the shaft being checked in a set of machinists centers fitted with one dial indicator, as shown in Fig. ______. Position the indicator on the middle of the shaft and then rotate it slowly. If the indicator shows a runout of over .001, replace the shaft. Also, when breakages of this type occur, check the condition of the transmission bearings.

5. The 5th/6th gear cluster on the main shaft, and 5th and 6th gears on the countershaft, are held in place by lock rings which fit into grooves cut in their shafts. These lock rings can usually be moved by rotating them around the shaft. However, if any lock ring can be moved up and down far enough that one of its edges is close to being out of its groove, or if it has an unusual amount of side play, replace the ring. See part C of this Section for proper procedure for replacing these rings.

6. Closely inspect each shifting fork for wear. The forks each have two thrust pads on their extreme ends. These pads are the only part of the fork that should make contact with the groove in the sliding gear. If a gouge or a wear mark appears on any other part of the forked end, that is a sign that the fork is either bent, or has been subjected to an unusually strong side loading force. In either case, replace that fork. Slide each fork back and forth along the entire length of the shift drum several times to insure that they are not binding. There should be oil on the surface of the drum when sliding the forks back and forth. Also, be certain to remove any burrs from the detent area of the drum, as they could damage the sliding surface of the fork.

7. With a vernier caliper, or 0 to 1 inch micrometer, measure each thrust pad on all three shifter forks (Fig. ____). They should all measure no less than .148. If any of them measures less, replace that fork.

8. Measure the width of the shifter fork grooves in the three sliding gears (Fig. ____). None of these grooves should measure more than .170. If any of them exceeds this, replace it.

9. Look closely at Fig. ____. It shows the manner and sequence in which the shifter forks are installed in the transmission shafts. The left fork is the 1st and 5th gear fork, mounted to the left sliding gear on the countershaft. The center one is the 3rd and 4th gear fork mounted to the sliding gear on the mainshaft. The right hand one is the 2nd and 6th gear fork, mounted to the right sliding gear on the countershaft.

10. There is a pin in the bottom of each shift fork that fits into one of three machined grooves in the shifting drum. You must now measure the diameter of each pin and measure the critical areas of its corresponding groove in the shift drum. This will tell you how much side movement the shift forks will have when they are engaged in each particular gear. If this side play is excessive, it could be the cause of a transmission jumping out of gear, or missed shifts. First, remove the cotter pin from one of the shift forks and remove the shifting fork pin. Measure the diameter of the part of the pin, which fits into the groove in the drum. Then measure the groove in the drum at its critical points. These critical points are where the pins experience the sharpest changes in direction when the drum is rotated. Repeat these measurements with the other two pins and drum grooves. In all cases none of the pins should measure less than .233 inches in diameter, and none of the grooves in the drum should measure more than .244 inches wide at the wear points. Replace any parts that do not meet these specifications.




Thrust pad, selector fork .155 in. .148 in.

Pin, selector fork .236 in. .233 in.

Grooves, shift drum .240 in. .244 in.

Groves, sliding gears .165 in. .170 in.


Section 3:

C.   Reassembly of the Transmission

1. The first step in assembling the Yankee transmission is to determine which gears go on which shafts, in what order, and facing what direction. There are two shafts in the Yankee gearbox, the mainshaft and the countershaft. The mainshaft is hollow and the countershaft is not. The left end of the mainshaft is threaded (for the clutch nut) while the right end of the counter shaft is threaded (for the countershaft sprocket nut).

2. To determine which gear goes on which shaft, measure the width of the machined portion of each gear at the base of the teeth (Fig. _____). Each of the mainshaft gears will be 13mm wide, while each of the countershaft gears will be 12mm wide. First gear on the mainshaft is difficult to measure; however, since it is the smallest gear in the transmission (18T) it is easy to remember. There are two steel bushings and two 2mm thrust washers in the transmission. Both bushings (which are identical) go on the countershaft, one for first gear and the other for second gear. One of the two thrust washers (which are also identical) goes on the left end of the mainshaft and the other goes on the right end of the countershaft.

3. On the mainshaft, 1st gear is the smallest gear and 6th is the largest. On the countershaft, the reverse is true; 1st gear is the largest and 6th is the smallest. Arrange the mainshaft gears from smallest to largest and you will have 1st gear through 6th gear. Arrange the countershaft gears from largest to smallest and you will have 1st gear through 6th gear. The proper order of gears on both shafts is, from left to right, 1st, 4th, 5th, 6th, 3rd, 2nd.

4. To be certain the transmission gears face in the proper direction, and that the bushings and thrust washers are in the proper places, refer to Figures ______ and ______in Part A of this section.

5. Select Yankee special tool No. 1120-505, circlip installing tool, and position it over the left end of the mainshaft (Fig. _____). Slide a new circlip (do not re-use the old ones) over the tool and push it down over the splines and into its groove with the outer portion of the tool. Slide the 5th/6th gear cluster into place on the mainshaft with 5th gear on the left. Using special tool No. 1120-511 on the right end of the mainshaft, install the second circlip. Now slide the remaining four gears and the thrust washer into position on the mainshaft.

6. Assemble the countershaft gears, bushings and thrust washer into place on the countershaft. The same special tools and procedures used on the mainshaft are used here. Again, be certain that 5th gear is to the left of 6th gear. The 1st and 2nd gear bushings are installed with their shouldered edge inward.

7. Remove any burrs, which may be present around the edges of the detent holes on the right end of the shift drum and slide the shift forks over the drum. All three shift forks are identical, however, they must be installed as shown in Fig. ______. When viewed from the left end of the shift drum, the two outer forks should point upward and to the right, the center fork upward and to the left, and the shifting fork pin bosses should be in a straight line and point downward. This is exactly how the shift drum and forks will appear in the assembled transmission.

8. It is not necessary at this time to install the selector fork pins.

9. Carefully inspect the three dowel pin holes in the transmission backing plate for signs of damage or elongation. Temporarily place the backing plate in place over the dowel pins in the main engine case. If there is any perceptible side to side movement, or if any of the dowel pin holes are elongated, the backing plate should be replaced. If the two ball bearings in the backing plate are to be replaced, remove them as described in Chapter 1, Section 8, and replace them as described in Chapter 3, Section 1.

10. Clamp the edge of the transmission backing plate in a soft, jawed vise as shown in Fig. _____. Assemble the entire transmission in your hands as it would appear in the engine. The shift forks should snap in place over their sliding gears with a small amount of resistance. Slide the entire transmission unit into place in the backing plate, making certain the thrust washer is in place on the mainshaft. If any shims were present when the transmission was removed these should be reinstalled now. Do not, however, consider this to be the final and correct shimming.

11. Position the main engine case as shown in Fig. ______. Slide the entire transmission upward and into place in the engine case. Make certain the dowel pins line up properly with their holes. The transmission is installed from the bottom so that the gears and thrust washers dont fall off the ends of the shafts. You can watch what is happening through the transmission inspection opening in the bottom of the engine case. Turn the engine upright and install the four small screws in the backing plate to hold the gearbox in place.

12. Using a vernier caliper or dial indicator, measure the end float, that is the total amount of side-to-side movement in both the transmission shafts and the shifting drum. The recommended end float is as follows:

Mainshaft - .1 to .2mm (.004 to .008)

Countershaft - .1 to .2mm (.004 to .008)

Shift Drum - .1 to .2mm (.004 to .008)

You should add or subtract shims as necessary to obtain the proper end float. Shims are placed on only the left end of the mainshaft, between the thrust washer and bearing; only the right end of the countershaft, between the thrust washer and bearing; and only the right end of the shift drum between the drum and the case.

13. Once proper end float has been obtained, install the transmission backing plate screws. The three long screws (35mm shank) go through the dowel pin holes, and the four short screws go through the remaining holes. A small amount of Loctite nut lock (blue) should be used on the threads of each screw. Warning: Use only nut lock on these screws. Any other type of Loctite will become too hard and will destroy the threads in the engine case the next time the screw is removed. Tighten the screws in a crisscross pattern until they are all just snug. Then, tighten them firmly with a large screwdriver or impact screwdriver. When the screws are tight, stake the outer edge of each screw to the backing plate using a hammer and center punch as shown in Fig. _____.

14. Install a new selector shaft O-ring in its groove in the right side of the main engine case. Select Yankee special tool No. 1120-441, O-ring protector and thoroughly grease its center bar as well as the sharp lip on the end of the tool. Slide the center bar all the way in, and insert the tool in the selector shaft hole. (Note: the tool will be more effective in the application if the set screw is removed form it. This will allow the selector shaft to pass all the way through the tool and protect the O-ring from the circlip groove in the shaft as well as from the splines.) Thoroughly grease the right end of the selector shaft assembly and insert it through its hole in the transmission backing plate. The center bar of the O-ring protector will be pushed out the other side. The outer portion of the tool should remain in the engine case until the selector shaft is fully seated against the transmission backing plate.

15. Push the selector shaft assembly all the way to the right, and measure the clearance between the tips of the selector pawl and the face of the shift drum (Fig. _____). There should be at least .015 in. clearance. If there is not, shim the selector shaft to the left by adding shims between it and the transmission backing plate until you have at least .015 in. clearance.

16. Slide the selector shaft retaining washer in place over the right end of the shaft, and install a new snap ring in its groove with the sharp edge of the ring facing outward.

17. Turn the engine upside down, and temporarily install the inner clutch hub, countershaft sprocket and gearshift lever. Install the shift detent assembly through the transmission inspection opening and turn it in finger tight. The plunger must apply some pressure to the detent holes. By turning the transmission shafts and operating the gearshift lever, shift the transmission through all six gears. If the transmission sticks between gears, hold one shaft stationary while turning the other. This will allow the engaging dogs to line up properly and the transmission will then shift. (This occasional sticking is normal when the engine is not running.)

18. It is possible to obtain nearly perfect gear engagement in every gear through the use of offset selector fork pins. As stated earlier, these pins are available in .1mm, .2mm, and .5mm of offset. The procedure for obtaining proper gear engagement is as follows.

19. Each shifting fork moves a sliding gear to the right to engage one idling gear and to the left to engage another. What sometimes happens is that the fork pushes its sliding gear too far in one direction and not far enough in the other. When this happens, an offset pin is used to move the shifting fork and its sliding gear in the direction that more engagement is needed.

20. Install the selector fork pins in the selector forks, and push the cotter pins through, but do not yet bend the ends over, as you may have to remove the pin. Shift the transmission into first gear, and look at the engaging dogs between 1st gear and 4th gear (the sliding gear) on the countershaft. The engaging dogs should be engaged approximately 75% to 80% of their length. Now shift the transmission to 5th gear and look at the engaging dogs between 5th gear and 4th sliding gear on the countershaft. Ideally, the amount of engagement between these engaging dogs should be the same as the 1st gear and 4th gear dogs. If the amount of engagement is not equal, use an off set selector fork pin to move the fork and its sliding gear in the proper direction to equalize engagement on both sides of the sliding gear.

21. This same procedure should be followed to check the engagement of the other four gears. Simply start with one shift fork, shift the transmission until that fork moves its sliding gear to engage a gear next to it, and check the amount of the engagement. Then shift the transmission until that fork moves the gear all the way in the other direction and engages the gear on the opposite side and again check engagement.

22. The left side (clutch side) selector fork engages 1st gear and 5th gear on the countershaft; the center fork engages 3rd gear and 4th gear on the mainshaft, and the right side fork engages 2nd gear and 6th gear on the countershaft.

23. If there is too little engagement between two gears, the transmission may miss shifts and perhaps not stay in gear. If there is too much engagement, the engaging dogs will bottom out on the face of its opposing gear.

24. When a sliding gear is in its center position (not engaged on either side), be certain the engaging dogs are not touching the dogs of the gears on either side.

25. When the selector forks are set up properly, the transmission shafts should spin freely in every gear as well as in neutral.

26. Install the two woodruff keys in their slots in the right end of the selector shaft. Push the selector return spring over the selector return arm and slide the arm into place on the selector shaft. Once the keys have been started in their keyways, tap the selector arm lightly inward until it seats against the circlip. Be certain the spring is between the arm and the case (Fig. _____), not outside the arm.

27. The only adjustment now necessary for proper operation of the transmission is the selector return mechanism. This adjustment is made by moving the eccentric selector spring anchor pin. This should be positioned so that on both upshifts and downshifts the selector pawl always returns over the top of the next selector pin in the end of the shift drum.

28. It is best to make this adjustment by shifting up and down from fourth or fifth gear, this way, the neutral detents in the drum do not interfere with the adjustment.

29. Shift from fourth to fifth, and slowly release pressure on the shift lever. If the shifter pawl does not return fully over the next pin. Loosen the lock nut on the eccentric pin and rotate the pin until the pawl does return. Now try a downshift from fifth to fourth. If the shifter pawl does not fully return, turn the eccentric pin back a small amount and again try an upshift and a downshift. If, after several attempts you cannot position the eccentric pin to obtain full return on both upshifts and downshifts, replace the selector return spring as it may have lost some of its tension.

30. Once the transmission is fully adjusted and working properly, tighten the shift detent screw with a large screwdriver or impact screwdriver. Make certain the cotter pins are installed in the shift fork pins. Reinstall the transmission inspection cover using a new gasket. Use a small amount of Loctite Nut Lock on the screws, and be careful not to over-tighten the screws as you can strip the threads with an impact screwdriver.


Section 4:

Repair Of Top End Components

1. This section will deal with repair and replacement of pistons and rings and preparation of the cylinders. The text deals with only one cylinder/piston unit at a time, however, the procedures apply to both cylinders on the 500 Z engine. In general, any change made to one cylinder should also be made to the other. If one cylinder is bored oversize, it is imperative that the other cylinder be bored to the same oversize.

2. When the engine was disassembled, you should have marked the pistons R and L for Right and Left. Upon reassembly, be certain you use the proper piston in each cylinder.

3. Thoroughly clean the cylinder and piston assembly. Visually inspect the cylinder for gouges, seizure marks, and noticeable wear. Check the piston for cracks or signs of noticeable wear.

4. Check the piston to cylinder wall clearance next. While doing this, the cylinder and piston should be at room temperature. (65 to 70 F.) Measure the piston at the bottom of the skirt from front to back, as shown in Fig.____. Measure the inside of the cylinder from front to back, approximately one inch up from the bottom of the cylinder liner as shown in Fig.______. Subtract the piston measurement from the cylinder measurement to obtain the piston clearance. The minimum allowable clearance for the 500 Z engine is .0015 inches. The maximum allowable piston to cylinder clearance is .005 inches. If your measurements exceed the maximum figure, you may need a new piston, or your cylinder may need re-boring.

5. To determine which solution is correct, clean the top of the old piston until you can find the number stamped on it (Fig._______). Then, compare the measured size of your piston with the size of an equivalent new piston, as given in the chart, Fig.______. If your piston measures less than the new one, subtract the size of the new piston from the inside diameter of your cylinder, and if the resulting clearance is within the allowable limits as shown in paragraph 4 of this Section, then the cylinder need not be bored if the piston is replaced with the new one of the same size.

6. If the tolerance would still be excessive with the new piston, this would necessitate boring the cylinder to the next oversize.

7. If the cylinder has worn excessively in one place, or been scratched deeply or gouged, the next oversize, being only .008″ larger, may not be enough to remove the defects. In these cases it will be necessary to go to an even larger oversize, or perhaps replace the cylinder liner.

NOTE: The piston to cylinder wall clearance is a very important factor in determining the performance of an engine. Too little clearance can cause piston seizure. Too much can cause a considerable loss in engine performance and efficiency. The accuracy of measuring this clearance is dependent upon the type and quality of the measuring equipment and the amount of time spent in using them to obtain the most accurate readings, both before and after boring. For this reason, it is recommended that unless you have the proper equipment for this task, and the knowledge of how to use it, you take the piston and cylinder to a qualified motorcycle shop or machine shop to have it bored or measured.

8. After boring and honing, the ports must all be beveled, or rounded, where they enter the cylinder. Bevel all the port edges with a .020 radius. This can be done with a small air or electric grinder or a very small machinists hooked file. If a small grinder is used, be very careful not to let it slip and scratch the cylinder wall. This beveling is very necessary, as it prevents the rings from catching in the ports as the piston passes them.

9. If you determine that there is not sufficient wear to warrant replacement of the piston, check the rings for freeness in the ring lands. If they are free, you must now carefully check them for wear. Remove them from the piston one at a time, being careful not to mix them up. You may even want to mark them top and bottom. It is also very important to mark each ring so that when and if you put it back on the piston it will have the same edge facing upward. Failure to do either of these things will result in accelerated ring wear and a loss of power.

10. Clean the rings thoroughly and place one of them inside the cylinder, approximately inch down from the top of the liner (Fig. _____). Take the piston and insert it into the cylinder upside down until the top of the piston hits the ring (Fig. ____). Then push the piston down another inch. This will make sure the ring is set squarely inside the cylinder. Remove the piston and measure the width of the gap at the ends of the rings as shown in Fig. _____. This distance should be from .075 to .085. Reinstall the piston and push the ring halfway down into the cylinder. Remove the piston and measure the end gap again.

11. Repeat this process with the other rings. If either ring exceeds the tolerance at either checking point, replace both the rings.

12. If the old rings are used, it will not be necessary to hone the cylinder. If new rings are fitted, it will be required to hone the cylinder enough to remove the glaze from the walls. Failure to do this will result in the rings taking an excessive period to seat, or perhaps not seat at all.

13. The correct procedure for honing a cylinder is to rapidly move the hone back and forth while it is turning. This results in a pattern called crosshatching. The crosshatching is correct when the small scratches made by the movement of the hone are at right angles to each other.

14. While honing, be careful not to remove excessive material from the cylinder. The idea is only to remove the oil glaze, which has been baked on the cylinder walls due to the heat of combustion.

15. Also, after honing, check the end gap of the new rings as described in Paragraph 10 of this Section. Since the rings are not marked, this will assure you that the rings you have are the correct ones for the piston you are using.

16. If you must replace the piston, the numbers and letters stamped on the top of the piston indicate its size in millimeters. Fig. _____ illustrates this.

17. Paragraph 4 gives correct piston to cylinder clearances to be observed when re-boring. This chart also shows the maximum allowable clearances. Naturally, a cylinder should be bored to minimum figure, .0015 in.

18. Even though exacting procedures are followed during the manufacture of pistons, they are not all precisely the same size. These very slight differences are denoted by a letter stamped on the top of the piston, an A., B., C., or D. A B piston is .0002 (2/10 of one thousandth) larger than an A. A C piston is .0002 larger than a B. A D piston is .0002 larger than a C.

19. This small difference in piston size is particularly helpful at the factory when the cylinders and pistons are selected for proper fit. Due to the large number of cylinders that the factory must produce, the finished inside size of each cylinder can vary perhaps .0002 to .0004 (2/10 to 4/10 of one thousandth). When each engine is being assembled, the assembler selects the piston (either A, B, C, or D) that gives the correct piston to cylinder clearance, thereby insuring maximum performance and piston life from that engine.

20. It is advisable to bore a cylinder to the smallest possible piston; i.e., A if possible, however it doesnt really matter if you have an A in one cylinder and a D in the other as long as they are the same oversize.



Piston Size Stamped Size Measurement in Millimeters Measurement in Inches

Standard 72 72.0 mm 2.8334 to 2.8344 in.

1st Oversize 72 S20 72.20 mm 2.8414 to 2.8424 in.

2nd Oversize 72 S40 72.40 mm 2.8492 to 2.8502 in.

3rd Oversize 72 S60 72.60 mm 2.8570 to 2.8580 in.


Section 5:


1. If the cylinder walls become worn or damaged to such an extent that even boring to the 3rd oversize will not repair it, or if the 3rd oversize has already been fitted and now has excessive clearance, the cylinder liner will need to be replaced with a new one.

2. To do this, place the cylinder in an oven and support it upside down by the fins, so that the liner will be free to drop out once it reaches the required temperature.

3. Set the oven to 550F. At approximately 500 to 550 , the liner should drop out of the cylinder (Fig.____). Occasionally the liner will hang up slightly inside the cylinder. This is due to the fact that at the factory, the ports in the liner are matched to the ports in the cylinder with an air grinder. This grinding sometimes results in a very small lip on the edge of the port between the cylinder and liner, and this lip catches the aluminum of the cylinder when the liner is being removed. When this happens the liner can be removed by gently tapping on its lower edge to assist it out of the cylinder.

Note: Do not drive, force, or press the liner from the cylinder. This will result in damage to the cylinder, which will impair its ability to transfer and dissipate the heat created during operation. DO NOT heat the cylinder to a temperature exceeding 750 degrees while attempting to remove the liner, or you face the danger of permanent cylinder distortion. If a liner proves to be particularly stubborn to remove, take it to a machine shop and have them turn down the inside of the liner on a lathe until it is thin enough to remove by gently breaking it apart.

4. After the liner is removed, allow the cylinder to cool and thoroughly clean the inside of it. Inspect for any gouges or scrapes that may have resulted when the liner was removed. If any such irregularities are present, carefully remove them with fine grit sandpaper, taking caution not to create a low spot in the cylinder by excessive sanding.

5. Place the cylinder back into the oven and heat it to 400 /450F. Remove it from the oven and support it right side up by the lower fins so that the liner can be dropped in from the top without hitting the bench.

6. Hold the liner just above the cylinder and turn it so that when it falls into the cylinder, the ports will be fairly close to being aligned.

7. The liner has an area on the bottom where its outside diameter is slightly smaller than the rest of the liner (Fig._____). This is to aid in starting it into the cylinder. Very carefully start this part into the cylinder, and continue moving the liner downward until it has moved one or two inches inside the cylinder. At that point, let go of the liner and it will drop into place inside the cylinder.

8. Very quickly turn the cylinder liner to align the ports, grasping it by the part that protrudes from the bottom of the cylinder (Fig.___). You have 6 to 10 seconds to do this once the liner falls into the cylinder.

9. Leaving the cylinder supported by the bottom fins, place a heavy weight on the top of the liner to hold it in place while it cools.

10. After the cylinder has reached room temperature, remove the weight and inspect the alignment of the ports. If there is a slight misalignment, correct it now with a suitable grinding tool. It is better to do this now, as should the grinding tool slip and scratch the cylinder wall, this scratch will be removed when the cylinder is bored.

11. All new liners require boring after installation. Therefore, refer to paragraph 4, Section 4, for the correct piston to cylinder clearance. Bore and finish the cylinder according to the instructions given in Section 4, paragraphs 13 through 20 of this chapter.


Section 6:


1. The Yankee crankshaft assembly is actually composed of two separate crankshafts connected by a coupling sprocket. These two crankshafts are identical except for the internal threads of the inner flywheel halves. The inner flywheel half of the right side crankshaft has right-hand threads, and that of the left side crankshaft has left-hand threads. This section will deal with the repair of a single crankshaft unit. However these procedures apply to either crankshaft.

2. All of the repairs that would be necessary on a Yankee crankshaft require the use of quite a few special tools. First, a press with a capacity of at least 15 tons is needed. A fixture for pressing apart the flywheels is required, along with a very special alignment jig for pressing them together. A set of machinists centers fitted with two dial indicators are also needed to check for alignment after reassembly of the crankshaft. For these reasons, we strongly recommend that you give the crankshaft to your Yankee dealer for repair. If he does not have the equipment to do it, he can send it to the Yankee distributor where a complete duplicate set of factory assembly line tools is used to facilitate any or all crankshaft repairs.

3. The crankshaft can be said to need repairs when:

a. The connecting rod is damaged.

b. The flywheels are not aligned within the given tolerances.

c. When either flywheel is damaged.

d. When the connecting rod, crankpin and bearing are worn or damaged.

e. When the connecting rods small end (wristpin hole) is worn or damaged.

4. The crankshaft flywheels must be in near perfect alignment to assure proper bearing and seal life, engine balance and ignition timing. If a set of machinists centers or a reasonable substitute is available, mount the crankshaft in them as shown if Fig. _____. Measured at the point where the main bearings mount on either side of the crankshaft, there should be no more than .001 run-out of the flywheels. If there is more, or you suspect misalignment of the crankshaft, but have no equipment for checking it, give the complete crankshaft assembly to your Yankee dealer for inspection and repair.

5. If the amount of clearance in the connecting rod big end bearing has become excessive, the connecting rod and bearing will need replacement. If you can detect a roughness in the bearing, or any perceptible up and down play in the connecting rod, it should be replaced. When replacing the big end bearing, it should be done as an assembly, that is, a new connecting rod, crankpin, rollers and roller cage. This is necessary because the rod is the outer bearing race, and the crankpin is the inner bearing race. To replace one of these without replacing them all is a waste of time and money, as the life expectancy of such a bearing assembly would be extremely short.

6. The wristpin bearing should also be checked for damage or wear. Clean the inside of the small end of the connecting rod, the wristpin and the wristpin bearing. Put the bearing into the small end of the connecting rod, then insert the wristpin. Position the wristpin so that the area of the pin that the needle bearings ride on is centered in the bearing. Hold the rod firmly with one hand, and try moving the wristpin in all directions to check for clearance (Fig. ____). If you can detect any noticeable play in this assembly, replace the wristpin and bearing and check it again. If no noticeable play is then evident, the old connecting rod assembly can be retained, using a new wristpin and bearing.

NOTE: Unlike the crankpin bearing assembly, the wristpin need not be replaced as a complete assembly. That is, the connecting rod need not be replaced every time you change the wristpin bearing. The crankpin bearing is subjected to heavy loads and direction changes while turning at a high RPM. The wristpin bearing is subjected to heavy loads and direction changes, but instead of rotating 360 on every revolution of the engine, it merely oscillates back and forth in an arc of less than 30. For this reason, individual components of the wristpin bearing can be installed to obtain the proper clearance, provided the components being reused are in good shape.



SECTION 1 Installation of New Bearings

1. Clean and inspect the main engine case. Carefully inspect all bearing mounting surfaces for signs of damage due to improper installation or removal of bearings. If the mounting surface appears very shiny, the bearing may have spun in the engine case. If so, Loctite Bearing Mount should be used when new bearings are installed. Also inspect the transmission backing plate dowel pin holes for signs of damage or elongation.

2. Press new bearings into the inner main bearing sleeves as well as the left side Jackshaft bearing sleeve. Note, the left main bearing sleeve is slightly larger in diameter than the right sleeve. The left Jackshaft bearing is a #6205 while both inner main bearings are No. 6205-C3. The C3 denotes greater clearance between the balls and races than in the standard 6205. The C3 bearings must be used for the inner crankshaft mains as there is greater load and therefore more heat generated at these points. When pressing these bearings into the sleeves, be certain to press only on the outer race of the bearing. Any amount of side load on the inner race of the bearing will mar the surfaces of the balls and races and the bearing will almost certainly fail.

3. Using Special Tool No. 1120-345, install the inner crankshaft seals in the main bearing sleeves. They should be pressed in just far enough so that the edge of the seal is flush with the edge of the sleeve.

4. Heat the main engine case to 250 - 300F. This takes about 25 min. in an oven set at 475F. Holding the main bearing sleeves with special tool No. 1120-321 (Fig._____) install them in the engine case. As you insert the sleeve into the case, align (as closely as possible) an oil hole in the bearing sleeve with the oil passageway in the transfer port. Using the same special tool, install the left side jackshaft bearing and sleeve. These sleeves must be fully seated in their mounting bosses. If the engine case is hot enough, the sleeves will slide easily into place. It is very important that you do not force the bearing sleeves into the engine case. Any excessive force will permanently damage the sealing surface between the bearing sleeve and the case.

5. While the engine case is still hot, install the two right side transmission bearings and the right side jackshaft bearing using special tool No. 1120-521 (Fig._____). All three of these bearings are No. 6304.

6. Again while the case is still hot, check all of the bearings and bearing sleeves you have installed to see that they remain fully seated in their mounting bosses. If any bearings have moved out slightly, you should be able to re-seat them by pushing them back into place with the blunt end of a hammer handle. If any bearings are not fully seated but will not move with gentle pushing, it will be necessary to re-heat the case.

7. Clean and inspect the right and left outer crankcase halves as well as the transmission backing plate. Again check for signs of a spun bearing and damaged or elongated dowel pin holes. Also inspect the gasket surfaces of the outer crankcase halves.

8. Heat the case halves and transmission backing plate to 250-300F. This takes about 10 minutes for the crankcase halves and 8 minutes for the backing plate in an oven set at 475F.

9. When the cases have reached the desired temperature, install the bearings as shown in Fig._____. They should simply drop into place. Make certain the bearings are fully seated in their mounting bosses. The outer main bearings in the crankcase halves are No. 6205, while the two bearings in the transmission backing plate are No. 6304.

10. The outer crankshaft seals will be installed after the final shimming of the crankshaft is completed.




1. Clean and inspect the crankshaft coupler bolt and remove any old Loctite from the threads. If the Allen hex sockets of the bolt appear to be damaged in any way, the bolt should be replaced.

2. Install a new O-ring on the coupler bolt.

3. Install new woodruff keys in their slots on the inner crank halves. Slide one of the crankshafts into place through its main bearings in the engine case, making certain you do not damage the seal with the woodruff key. The cranks are marked R (or D) and L (or I) for right and left. Be certain you install them properly.

4. Slide the crankshaft into the coupler sprocket inside the case, making certain the woodruff key fits into its keyway in the sprocket. Also, make certain the primary drive chain is in place around the sprocket.

5. Start threading the coupler bolt into the inner crank half of the remaining crankshaft. Remember, one end of the bolt has right-hand threads and the other end has left-hand threads. Screw the coupler bolt in one complete turn.

6. Insert Special Tool No. 1120-341 through this crankshaft and into its hex in the coupler bolt.

7. Install the second crankshaft in the engine case. Slide it in until the coupler bolt comes in contact with the first crankshaft, and slowly turn the bolt (clockwise from the left side of the engine, counterclockwise from the right side) until you feel the bolt threading into the first crank. Ideally, the bolt should start threading into both cranks simultaneously. You can, however, be up to one complete turn off as long as you dont exceed this limit.

8. Once the threads have started properly in both crankshafts, continue to turn the coupler bolt and thereby draw the crankshafts together. The important point to remember here is that one of the woodruff keys is in its keyway (the first crank installed) but the other key (second crank) is not necessarily in its keyway. As you draw the crankshafts together, try to line up the key with its keyway. By turning one crank slightly back and forth as the two come together, you will be able to feel when the second key is in its keyway. When you are certain both keys are in their keyways, draw both cranks together as far as they will go.

9. Using Yankee Special Tool No. 1120-121, mag holding tool, hold the crankshafts from turning (Fig.____). Tighten the coupler bolt to 65 ft. lbs. Of torque.

10. Reinstall any shims that were present on the ends of the crankshaft when the engine was disassembled, and install both outer crankcase halves, using new gaskets between the mating surfaces. Use only four screws to hold each case half in place, however tighten the screws firmly to compress the gaskets. With a sharp knife, trim away any excess gasket material that protrudes from between the cases both on top of and inside the case gasket areas.

11. Using a plastic or fiber mallet, lightly tap the crankshaft all the way to the left. You can measure the end float of the crankshaft by measuring the gap between the inner race of the right outer main bearing and the right side of the crankshaft with a feeler gage (Fig.____). This can also be measured with a vernier caliper or a dial indicator on the end of the crankshaft. Measure the total amount of side to side movement of the crankshaft.

12. The proper crankshaft end float is .006 in. to .012 in. If your measurement does not fall within these tolerances, add or subtract shims accordingly to achieve the proper end float. If you must add or subtract shims, try to keep them equally distributed on both ends of the crankshaft to make the job of centering the cranks easier.

13. Once proper end float has been established, it is necessary to check the centering of the crankshaft. It may be necessary to remove shims from one end of the crankshaft and place them on the other end to insure that the connecting rods run midway between the flywheels. The procedure for checking this is as follows.

14. Obtain two old Yankee pistons of the same oversize as the cylinders and cut the tops from them (Fig.____). Install these pistons on the connecting rods using your wrist pins and wrist pin bearings. It is not necessary to install the circlips.

15. Slide the cylinders in place over the centering pistons, and look down at the connecting rods through the tops of the pistons. With a plastic or fiber mallet, lightly tap the crankshaft all the way to the left. Rotate the crankshaft 3 or 4 revolutions, and observe where the connecting rods run in relation to the sides of the crankshaft flywheels. Then, tap the crankshaft all the way to the right and repeat the test.

16. Ideally, the connecting rods should run in the center of the crankshafts, equidistant from the right-side and left-side flywheels. If the rods seem to run too close to the right side flywheels of each crank, remove shims from the right end of the crankshaft and place them on the left end of the crankshaft to move the crankshaft to the right. If the rods are too close to the left-side flywheels, move shims from the left end of the crankshaft to the right end. Do not add or subtract any shims, simply move them from one end of the crankshaft to the other end until the connecting rods run in the center of the flywheel halves.

17. If the crankshaft is centered properly but the connecting rods run too close to the outer flywheel (right rod too close to right outer flywheel, left rod too close to left outer flywheel) this can be remedied by installing Yankee Part No. 1101-457, crankshaft coupler sprocket (oversize). This oversize sprocket is designed to spread the crankshafts apart about .012 in. more than the standard coupler sprocket. If this oversize sprocket is used, it will be necessary to re-shim the crankshaft for proper end float and centering.

18. Once proper end float and centering has been established, remove the cylinders and centering pistons. Remove the outer crankcase halves, and place any shims that may have stuck to the bearing over the appropriate end of the crankshaft.

19. Using Yankee Special Tool No. 1120-345, crankshaft seal installing tool, install new seals in the outer case halves. They should be pressed in far enough so that the edge of the seal is flush with the surface of the case.

20. Apply a small quantity of high temperature grease to the sealing lips of the crank seals and install the outer crankcase halves, making certain the gaskets are in place.

21. Apply a small amount of Loctite Nut Lock (blue) to the case screws and install the screws, tightening them with an impact screwdriver. Do not use any type of Loctite other than nut lock, or the threads in the engine case could be permanently damaged. When all of the screws are tight, stake the outer edge of each screw to the engine case using a hammer and center punch (Fig._____).




1. The top end components must meet the criteria described in Chapter 2, Section 4, before they can be installed.

2. Make certain the center case gasket edges are flush with the base gasket surfaces of the case. Squirt a small amount of oil into the main bearing oil holes drilled into the transfer port cutouts.

3. Wrap clean shop rags around the connecting rods to prevent any parts or foreign material from falling into the crankcases. Slide new base gaskets over the studs and trim away any excess gasket material, which may partially block the transfer ports.

4. The piston, wrist pin, wrist pin bearing and connecting rod (small end) are all color coded to allow for a perfect fit upon assembly. The piston and wrist pin are coded either black or white. You must use a white pin with a white piston, and a black pin with a black piston as the diameters of the pin and its hole in the piston are slightly different. The wrist pin bearings are available in four sizes. Choose the proper bearing depending upon the color of the con rod and wrist pin. The chart, Fig.___, shows which bearing you will need.

NOTE: If you are in doubt as to which wrist pin bearing you possess, put the bearing inside the connecting rod and insert the wrist pin into it. The pin should be easy to slide through the bearing. Once you have the pin in place, hold the rod firmly with your fingers and try to wiggle the wrist pin inside the bearings. If any play in detectable between the pin and bearing, or if any force is required to push the pin into it, you have the wrong bearing and it should not be used.

5. Squirt a few drops of oil into the wrist pin bearing you have selected and insert it into the connecting rod.

6. Clean the wristpin in a solvent, and push it part way into the piston. Work it back and forth until it can be pushed in and out freely with your fingers. Again clean the wrist pin, and push it part way into the piston. Set the piston on top of the connecting rod with the arrow on top of the piston pointing forward. Be certain you use the right piston on the right side and the left piston on the left side if the pistons are so marked.

7. Align the piston and connecting rod properly by sliding the Yankee wrist pin drift (No. 1120-211) into the piston and through the wrist pin bearing until it butts up against the end of the wrist pin.

8. Support the piston with one hand to prevent side loading the connecting rod and push the wrist pin inward with the other until the wrist pin drift drops out (Fig.____).

NOTE: Do not attempt to position the wrist pin by hammering it with a mallet, as this may bend the

connecting rod. If the wrist pin proves difficult to move, use a wrist pin driving tool as shown in

Fig. ____to install the pin.

9. Using a pair of needle nose or duck bill pliers, install both wrist pin clips in the piston. If you can rotate either of these clips in both directions in their grooves after installation, remove and discard them and install new ones.

10. Install both rings on the piston, making sure that the small peg in each ring groove is centered between the ends of the ring. Be certain that neither ring can bind in its groove. Squirt a few drops of oil on the rings and work it around to lubricate all of each ring.

11. Repeating this procedure, install the second piston and rings on the remaining connecting rod.

12. Remove the shop rags and turn the engine very carefully until one of the pistons is at bottom dead center (B.D.C.). Slide the cylinder down over the studs until the bottom of the liner rests squarely on the top ring.

13. The bottom inside of the cylinder liner has a small chamfer machined around its circumference to make the rings easier to start into the cylinder. Using your fingers, or a ring compressor, compress the rings, being careful not to allow either ring to ride up over the peg in its groove. Carefully work the cylinder down over the piston and seat the cylinder against the engine cases. Applying a small amount of oil to the chamfer will make installation much easier.

14. Install the second cylinder in the same manner. Once both cylinders are in place, rotate the crankshaft a few times and remove any dust or dirt that may have collected at the top of the cylinders.

15. Inspect the mating surfaces of the cylinder heads and the top of the cylinders. Make certain these two surfaces are smooth and clean.

16. Place a new head gasket on each cylinder and center it on the top of the liner.

17. Slide the heads down the studs into place on the cylinders. The higher ends of the cooling fins are on the front of the heads. Fit the flat washers to the cylinder studs and mount the eight 12mm nuts, turning them down finger tight.

18. Fit a 12mm socket to a low reading torque wrench and torque the nuts to 5 ft. lbs. (60 inch lbs.) using the sequence shown in Fig.____. Repeating this sequence a second time, torque the nuts to 10 ft. lbs. (120 inch lbs.). Repeat a third and final time, using 15 ft. lbs. (180 inch lbs.).

NOTE: If you attempt to tighten the cylinder heads in any other sequence, without a torque wrench, or

with a torque wrench that is not accurate at very low readings, you run the risk of warping a

cylinder head or causing piston seizure due to cylinder distortion.

19. Once the top ends are in place, the engine should be pressure checked for air leaks. The sparkplugs and compression releases should be installed in the heads, and the exhaust and intake ports blocked off. The magneto flywheel bolts must be installed in the ends of the crankshafts. The most important areas to check for leaks are the base gaskets, inner and outer crank seals, and the inner main bearing sleeves where they mate to the engine case. If any leaks are discovered, they must be corrected before assembly continues.




1. The Yankee 500 Z is fitted with two separate Motoplat solid-state electronic ignition systems, one for each cylinder. These two systems are identical in operation. The only difference between them is that the right side flywheel turns in a clockwise direction, while the left side flywheel turns in a counterclockwise direction. There is an arrow on the outer perimeter of each magneto flywheel, which indicates direction of rotation. There is a reference number stamped on the face of the flywheel. This number is also stamped on the stator. Each flywheel/stator unit is a matched set, so this reference number must be the same on both flywheel and stator. You cannot use the flywheel from one Motoplat unit with the stator from another unit.

2. Examine each Woodruff key that locates the magneto flywheel on the crankshaft. If it shows any signs of wear or damage, replace it with a new one. Before fitting it into its slot in the crankshaft, lay it upside down on a hard surface and tap its rounded edge with a ball peen hammer, as shown in Fig. ____. This will very slightly widen the key so it will fit tightly in the slot and be less likely to dislodge while you are installing the magneto flywheel. Tap the keys into their slots in the crankshaft.

3. Closely examine each magneto stator for broken or cut wires or other apparent damage. Without using any harsh solvents, clean the stators thoroughly and blow them dry with compressed air. Be especially careful to remove any trace of metal filings that may be on the stators.

4. Slide the stator wires through the holes in the crankcase halves, and install the rubber grommets.

5. When you disassembled the engine you were instructed to scribe a reference line across the edge of the magneto stator and one of its mounting bosses on the engine case. Locate these marks and position the stator on the engine so that they are aligned. Install the three backing plate mounting screws and tighten them. Be certain you have the right stator on the right side and the left stator on the left side.

6. Select the right side magneto flywheel and position it in front of the crankshaft. Look through the hole in the center of the flywheel and turn it until the slot in the center is aligned with the Woodruff key on the crankshaft. Mount the flywheel on the crankshaft, pressing it into position with your hands. Tap on the face of the flywheel with the side of your hand to be sure that it has seated fully on the crankshaft. Do not install the nut.

7. When timing the Yankee engine, each cylinder is timed individually. Complete the timing procedure on one cylinder before starting on the other.

8. You will now need a dial indicator to locate the position of the piston while timing the engine. There are several types of dial indicators and sparkplug hole adapters available through most motorcycle accessory distributors or machinist supply firms. Since most of them are similar, the procedures for using them are usually the same.

9. Most timing dial gauge kits consist of a dial gauge calibrated either in millimeters or thousandths, an adapter that screws into the sparkplug hole, and a plunger that fits into the adapter, between the piston and the indicator (Fig.___). To install the gauge remove the sparkplug and screw the adapter tightly into the hole. Drop the plunger down through the center of the adapter and then set the dial indicator into the center of the adapter.

10. Slowly turn the flywheel while lightly holding the dial indicator. Continue to turn the flywheel until the piston comes up to the top of its stroke (T.D.C.). With the piston at Top Dead Center, gently push the dial indicator downward until the small needle registers 4mm. Tighten the locking screw on the adapter, which will lock the indicator in place.

11. Move the flywheel back and forth slightly until you are certain you have T.D.C. Then, rotate the face of the indicator so that the large needle reads zero (Fig.___).

12. Now turn the flywheel opposite the direction of the rotation of the engine (turn it clockwise if you are timing the left cylinder and counterclockwise if you are timing the right cylinder) until the needle completes 2.75 revolutions (2.75mm). Note, since you started at 4mm, and you are moving the indicator backwards, the gauge will now read 1.25mm.

13. Insert the timing pin, Yankee Special Tool No. 1120-111, through the small hole in the flywheel. If the magneto is timed properly, the pin will pass directly through the hole in the flywheel and into its corresponding hole in the stator.

14. If the pin does not pass into the hole in the stator it will be necessary to remove the flywheel and rotate the stator slightly in the appr9opriate direction until the pin will pass through the flywheel and into the stator at 2.75mm BTDC.

15. Once the proper timing has been attained, tighten the three stator mounting screws securely, slide the flywheel back onto the crankshaft, and again check the timing. Remove the dial indicator, plunger, and adapter.

16. Fit a new star lock washer to the crankshaft and a new O-ring on the end of they flywheel mounting bolt. Apply a few drops of Loctite to the threads of the bolt, and turn it in finger tight. Fit the Yankee flywheel holding tool (No. 1120-121) to the slots in the flywheel. Using a 26mm socket, torque the magneto flywheel nut to 60 ft. lbs. (Fig.____).

17. Sometimes the Woodruff key that locates the magneto flywheel on the crankshaft is slightly narrower that the keyway on the flywheel into which it fits. Because of this, it could be possible for the flywheel to shift slightly when the nut is torqued. For this reason, many mechanics prefer to make a precautionary timing check after the nut is torqued. Although the amount that the timing could change is very small, this final check is worth doing.

18. Repeat the timing procedure with the second cylinder, again timing is at 2.75mm BTDC.




Section 1

0 to 1/8 Throttle: The Pilot Metering System (Fig.____).

1. The pilot metering system feeds fuel and air from 0 to 1/8 throttle. The fuel is metered by the pilot fuel jet. Air is metered by the low speed air screw and the carburetor slide.

2. When the throttle is closed and the engine is idling, the upward movement of the piston creates a vacuum in the intake port. This vacuum causes air to be sucked into the left-hand hole beneath the intake mouth of the carburetor. This air flows through a passage that leads to the low speed air screw. This screw meters the amount of air available to flow past a small orifice that connects to the pilot fuel jet.

3. At this orifice, the fuel and air are mixed together and then flow into the carburetor bore through a small hole just in front of the slide. The mixture then enters the engine.

4. As the throttle is opened just slightly, the fuel mixture can also enter the engine through another small hole just inside the front edge of the slide. Due to the slide being raised slightly, larger amounts of air flow over these two holes, causing more fuel to be drawn up out of them.

5. You can vary the proportion of the mixture from 0 to 1/8 throttle by changing the pilot fuel jet. A larger number jet will make the mixture richer: a small number jet will make it leaner.

6. You can also vary the mixture from 0 to 1/8 throttle by adjusting the low speed air screw. Turning this screw clockwise makes the mixture richer: turning it counter-clockwise makes it leaner.

7. The pilot metering system continues to work in conjunction with other metering systems at larger throttle openings, although its influence is greatly decreased.

Section 2

1. You will notice that the carburetor slide has its bottom edge cut away on the air intake side. This is called the slide cutaway.

2. There is a tube protruding from the bottom of the carburetor bore. This tube is called the needle jet. The tapered needle in the slide projects down into this tube, and as the slide is raised, the needle is drawn up out of the tube, metering the flow of fuel accordingly.

3. As the slide moves from 1/8 to throttle, air flows past the needle jet. If the air could flow squarely across the top of the needle jet, it would create considerable vacuum in it, therefore sucking too much fuel from it. This is the reason for the slide cutaway, so as to direct air downward against the mouth of the needle jet. This decreases the amount of vacuum formed, thereby decreasing the amount of fuel flow.

4. The higher the cutaway (stamped in millimeters on the bottom of the slide) the smaller the fuel flow (leaner mixture). The lower the cutaway, the greater the fuel flow (richer mixture).

5. The mixture at 1/8 to throttle can be varied in two ways. A needle jet with a larger hole could be fitted. However, the selection of these needle jets is limited. It is always best to vary the mixture at 1/8 to throttle by installing a slide with a higher or lower cutaway.

Section 3

to Throttle: Needle Position and Booster System (Fig.____)

1. From to throttle, the slide regulates the flow of air. As the slide is raised further above the top of the needle jet, the cutaway becomes decreasingly effective in directing the air downward. Because of this, the air flows more squarely across the top of the needle jet. This increases the amount of vacuum formed in the needle jet, thereby drawing a greater amount of fuel from it.

2. At this throttle opening, the flow of fuel is regulated by the tapered needle. As the slide moves from to throttle, the needle is withdrawn proportionately from the needle jet, thereby allowing for a greater flow of fuel.

3. The mixture at to throttle can be adjusted by raising or lowering the needle. The needle is suspended in the slide by means of a clip fitted to one of three grooves in the needle. Putting the clip in a lower notch raises the needle, making the mixture richer. Moving the clip to a higher groove lowers the needle, making the mixture leaner.

4. Because the venturi of the carburetor is round, a small upward movement of the slide at or near throttle position will allow for a much larger volume of air to flow through the carburetor bore than the same movement at a higher or lower throttle opening. This creates a greatly increased demand for fuel. The needle jet cannot supply this fuel alone, because only the volume of air flowing over it has increased, not the vacuum created in it. To compensate for this, a booster system is provided.

5. To boost the flow of fuel, air enters the center small hole beneath the intake mouth of the carburetor. (Fig.___) This air is routed directly to the needle jet through several small holes drilled halfway up it. This passage of air up the needle jet boosts the flow of fuel which is necessary to meet the demand. Although the booster system is working at all throttle openings above idle, it is most effective around throttle. There are no provisions for adjustment of the booster system on the 24 mm and 27 mm IRZ carburetors.

6. The proportion of the mixture at to throttle also affects the mixture at greater throttle openings.

Section 4

to Full Throttle: Slide and Main Jet (Fig.____)

1. From to full throttle, the additional flow of air is regulated by the position of the slide. As the slide nears the top of the bore, the cutaway has little or no effect. A higher vacuum is then created at the needle jet, drawing out an increasing amount of fuel.

2. As the needle is raised higher in the needle jet by the upward movement of the slide, it becomes less effective in metering the flow of fuel accurately. From to full throttle, the main jet controls the flow of fuel.

3. To vary the mixture from to full throttle, fit a main jet with a higher number to make it richer, or with a lower number to make it leaner.

4. NOTE: Each metering system blends gradually with the one preceding it and the one following it. The objective of regulating the carburetor is to arrive at a condition wherein there is a smooth transition from one metering system to the next and the proportion of fuel and air remains the same from closed to full throttle.

Section 5

The Float Metering Device (Fig. ___)

1. The float mechanism provides a constant level of fuel for the fuel metering system. This constant fuel pressure allows for an even rate of flow through the jets.

2. When the fuel flows through the float metering jet in the top of the float bowl, the fuel level in the bowl rises. This causes the float to rise and push the float needle up into the float metering jet. When the fuel reaches a predetermined point, the float will have risen to a point that is sufficient to fully seat the float needle in the metering jet, stopping the flow of fuel.

3. The float level is not adjustable on the 24mm 27mm IRZ carburetors.




1. When tuning the Yankee 500 Z carburetors, it is imperative that the two carburetors be in complete synchronization. Make certain that the jet size, needle size and position, and slide cutaway are identical in both carburetors.

2. Any time a carburetor slide or cable is replaced, the carbs must be re-synchronized.

3. To adjust the idle speed, start the engine, and let it warm up to operating temperature. Make the following adjustments with the engine running. If the engine is equipped with a manifold balance tube, the tube should be temporarily blocked off (not disconnected) before adjusting the carburetors.

4. The Idle RPM Screws, Fig._____, which are the spring-loaded screws on the left side of each carburetor, should both be screwed in the same amount. If one screw seems noticeably shorter or longer than the other one, back out the short one and screw in the long one until they are both adjusted the same.

5. Now adjust the idle screws to attain the desired idle speed. Turn each screw only a quarter-turn at a time, and alternate from one screw to the other. Turn the screws clockwise to increase idle RPM, counter clock-wise to decrease RPM.

6. Adjust the idle mixture screws (low speed air screws). On the right side carburetor, turn the idle mixture screw in either direction until the engine RPM begins to fall off. Using that as a starting point, turn the screw in the opposite direction, counting the number of turns until engine RPM again begins to fall off. Now turn the screw in the original direction one-half the number of turns you just counted.

7. Repeat paragraph 6 above with the idle mixture screw of the left side carburetor. Both screws should end up between and 1-1/2 turns out from the fully seated position.

8. Readjust the idle RPM Screws as in paragraph 5 to again achieve the desired idle speed.

9. Shut off the engine, and disconnect the rubber air cleaner hose assembly from the carburetors. Open the throttle as far as it will go, and stick you fingers into the bores of both carburetors. Both slides should have pulled up past the top edge of the carburetor bores. If either one is sticking down past the top of the bore and cannot be raised past it with the cable adjuster, the cable should be replaced.

10. With both slides fully up, slowly release the throttle until the slides just begin to lower past the top edge of the bores. Both slides should reach this point at the same time. If they do not, reset the cable adjusters so that both slides lower simultaneously.

11. Now release the throttle and see that both slides seat fully. There should be approximately 1/16 inch free play in both cables. If there is not, both cable adjusters should be reset to obtain the necessary free play, and then re-synchronized as in paragraph 10.

12. Replace the air cleaner boot and clamps, and readjust the idle speed screws if necessary.




Section 1: Operation of the Ignition System

1. The Yankee 500 Z is fitted with two separate Motoplat solid-state electronic ignition systems, one for each cylinder. These two systems are identical in operation. The only difference between them is that the right side flywheel turns in a clockwise direction, while the left side flywheel turns in a counterclockwise direction. There is an arrow on the outer perimeter of each magneto flywheel which indicates direction of rotation. There is a reference number stamped on the face of the flywheel. This number is also stamped on the stator. Each flywheel/stator unit is a matched set, so this reference number must be the same on both flywheel and stator. You cannot use the flywheel from one Motoplat unit with the stator from another unit.

2. Each Motoplat ignition system consists of four basic parts:

a. A rotating magnet called a magneto flywheel.

b. A set of stationary coils, wires and diodes encased in epoxy resin. This is called a magneto stator.

c. A device similar to an ignition coil called an electrical converter.

d. A sparkplug

3. The magneto flywheel contains permanent magnets. When these magnets pass the low voltage coils on the magneto stator an AC current is formed in the coils.

4. The AC current formed in the low voltage coils then goes through a diode, which is a small electrical component that, among other things, allows current to pass through it in only one direction. Therefore, the current on the other side of the diode is DC current.

5. This DC current flows to the electrical converter or high voltage coil on the frame and charges a capacitor housed within the coil.

6. The capacitor is connected to a silicon controlled rectifier or thyristor. This thyristor will not allow the current to discharge from the capacitor until it is triggered by a separate voltage.

7. When it is time for the sparkplug to fire, a special magnet in the flywheel passes by a pickup coil on the stator. This generates a small current in the coil and it flows to the thyristor and triggers it, allowing the capacitor to discharge its current through the primary windings of the high voltage coil. As a result, a high voltage is formed in its secondary windings and the sparkplug fires.

8. To regulate the time at which the sparkplug fires, you simply rotate the magneto stator in one direction or the other on its mounting bosses. This changes the time at which the special magnet passes the pickup coil on the stator. See Part A, Chapter 3, Section _____, for details on regulating the engine timing.

9. On the Yankee Z, the magneto stator is also wired to provide charging current for the lighting system.




1. If the engine wont run at all, runs on only one cylinder, is difficult to start, or runs very poorly and you suspect the ignition system is at fault, remove both sparkplugs from the engine. With the ignition switch turned off, operate the kickstarter a few times to remove any gasoline from the cylinders. This is to eliminate any chance of fire when testing for spark. If there is any gasoline present on the cylinder heads, let it evaporate before continuing. Fit each plug into its sparkplug cap and ground the base of each plug against the cylinder head (as far away from the sparkplug hole as possible). Turn the ignition switch on and operate the kickstarter. Watch and listen for a healthy spark at both sparkplugs. If you get a weak spark or no spark at all in one (or both) sparkplug (s), substitute new plugs and perform the test again. If you still get no spark or weak spark, the following items should be checked.

2. Remove the sparkplug cap (or caps), check for moisture corrosion, and be sure it has good contact with the stranded metal portion of the plug wire. Check for spark again.

3. If you still get no spark, remove the gas tank and check the high voltage coil mounting brackets for proper grounding. Also, check the blue and black coil leads from each magneto for moisture and corrosion. Reinstall the coil leads on their proper terminals, making sure they are a tight fit. Again check for spark.

4. If you still do not get a good spark at both plugs, remove the blue wires from terminals #8 and #11 of the ignition switch. These blue wires are the kill wires for the high voltage coils. When these wires are grounded, the coils will not fire. Be certain these wires are not touching any metal surfaces or each other, and again test for spark. Note, these wires are connected to separate terminals on the ignition switch, which are grounded when the switch is turned off. These wires must never be connected together to a single terminal kill switch, as ignition timing will be adversely affected. This is especially true if your cylinders are not firing simultaneously. (See Chapter 2, Section 2, paragraph #_____.)

5. If you now do get a proper spark at each sparkplug, the ignition switch is faulty and should be replaced.

6. If you still do not get proper spark to both plugs, remove the magneto covers from both sides of the engine, and closely inspect the wires that run from the magneto stators to the high voltage coils. Using a test light or an ohmmeter, test the wires for continuity from the terminals on the coil to the base of the wires at the stator. You must eliminate the possibility of a break (open circuit) or short in these wires. Test for spark.

7. At this point, you should be getting a good spark from at least one of the sparkplugs. You have eliminated every item that could malfunction except for the mags and coils themselves. It is highly unlikely that both mags or both coils are faulty at the same time.

8. Assuming one cylinder now has proper spark, we can determine whether it is the coil or the mag of the other cylinder that is faulty simply by switching the magneto leads (black and blue wires) from one coil to the other. Remove the mag leads from the coil that was producing spark and attach them to the coil that was not producing spark. Also, attach the mag leads from the non-sparking coil to the coil that was producing spark. Now test for spark as before.

9. If the coil that was producing proper spark still does so, both magnetos are working properly, and the non-sparking coil is bad. If the spark is now occurring at the opposite sparkplug (the one that wasnt working before) then the magneto for that side is bad.

10. Further checking of the ignition components requires the use of specialized equipment such as an oscilloscope. For this reason, if you still cannot determine which component is faulty, the best practical method for repair is to first substitute a new coil for the one on the motorcycle and test for spark. If the spark is then sufficient, you will of course, know that the old coil is defective. If you still get a weak spark, or no spark, reinstall the old coil and substitute a new magneto.

11. STROBE TIMING. If the motorcycle runs, but it lacks power and gives erratic sparkplug readings, it is possible that the magneto is producing sufficient spark, but is doing so at the wrong time, even though the magneto has been timed properly with the timing pin and dial indicator. This can easily be checked stroboscopically with an automobile type timing light.

12. First, set the timing on each cylinder as described in Part A, Chapter 3, Section 4. When you are finished, before removing the timing pin, make a line across the top of the flywheel with a piece of chalk or other suitable marking device and put a corresponding mark across from it on the engine case, as shown in Fig.___. Remove the timing pin.

13. Connect the timing light to the right side plug wire, and if it is the type that needs an external source of power, provide that source (battery, wall outlet, etc.) according to its need.

14. Start the engine and let it idle. Aim the timing light at the right side flywheel, as shown in Fig.___, and watch the marks. The mark on the flywheel will be slightly to the right of the mark on the case. Accelerate the engine to approximately 6000 R.P.M. At the point the timing will have fully advanced and the mark on the flywheel and the mark on the case should appear to be aligned.

15. If the marks did not align, turn off the engine and adjust the timing by removing the flywheel and rotating the stator. If the mark on the flywheel was to the right of the mark on the case, turn the stator counterclockwise an equivalent amount. If the mark on the flywheel was to the left of the mark on the case, turn the stator clockwise an equivalent amount. Reinstall the flywheel and check the timing again with the light.

16. If the mark on the flywheel was erratic and seemed to fire almost anywhere, or jump around quite a bit, replace the magneto.

17. Repeat steps 13 through 16 of this Section, using the left sparkplug wire and left magneto flywheel. The only difference you should see is that the timing mark on the left flywheel will be to the left of the stationary mark at idle and should advance toward the right as R.P.M. increase. Again the marks should be aligned at approximately 6000 R.P.M.




Section 1: Operation

1. The YANKEE 500 Z is equipped with a battery operated lighting system. Alternating current is generated in two separate magneto/flywheel assemblies by permanent magnets in the flywheels passing over the lighting coils in the stators. Unlike the ignition circuits, which work independently, each charging circuit works in conjunction with the other to produce the total charging current.

2. The alternating current produced by the two magnetos is rectified and regulated by diodes in the regulator. The direct current produced at the regulator flows along a white colored wire to terminal No. 3 of the main switch. The current then flows from terminal No. 2 of the switch (when the switch is on) through a 15-amp fuse and into the battery.

3. The amount of current allowed to pass through the regulator and into the battery is dependent upon the amount of charge in the battery and the amount of drain or discharge on the system. This is accomplished through a feedback circuit from the battery to the regulator. The minimum battery voltage necessary to operate the regulator is 3.3 volts. If the battery voltage is less than this figure, no charging current will be produced by the regulator. When battery voltage reaches the maximum rated value of the regulator, 7.5 volts, and there is no drain on the system (lights turned off) the charging current will be reduced to zero.

Section 2: Checking the Charging Circuit

1. The first step in trouble shooting any electrical malfunction is to check all connections to make certain they are tight. Check all wires for shorts, and see that the correct wires are connected to one another. Also, see that the fuse (15 amp) is in good condition.

2. If the battery does not seem to be charging properly, remove it and charge it for several hours on a 6 volt battery charger rated at one amp or less. If the battery holds the charge, reinstall it and if it does not, replace it.

3. If the battery, wiring and fuse are all OK, disconnect one of the red wires from the double terminal (marked R- R) of the voltage regulator. Connect the positive lead of a DC ammeter to this wire and connect the negative lead of the ammeter to the now empty terminal of the regulator. The meter must be capable of registering at least 15 amps.

4. Connect the positive lead of a DC voltmeter (set on 10 volt scale) to the positive battery terminal, and ground the negative lead of the meter. The meter must show at least 3.3 volts. If not you must recharge the battery.

5. Turn the main switch to on, start the motorcycle, and accelerate the engine to approximately 3000 R.P.M.

6. Switch on the lights. If the voltage of the battery reads less than 7.5 volts (but more than 3.3 volts) the ammeter should read approximately 11 amps.

7. Switch off the lights and maintain 3000 R.P.M. The battery voltage should slowly increase to the rated maximum value of the regulator; 7.5 volts while the charging current should slowly decrease to zero amps. If the charging current does not decrease to zero but the battery is fully charged, replace the regulator and repeat the test.

8. If in paragraph 6 above, the battery is not fully charged but 11 amps cannot be attained, either the regulator or one of the magnetos is faulty.

9. To determine whether it is the regulator or one of the mags which is at fault, disconnect the DC ammeter and voltmeter from the motorcycle. Disconnect the Red, Yellow, and White wires at the regulator. These wires are in the same harness, and connect both magnetos to the voltage regulator.

10. Start the motorcycle and accelerate the engine to 3000 R.P.M. Using an AC voltmeter on a 0 to 50 volt scale, measure the voltage between the Red wire and White wire. Next, measure the voltage between the Red wire and Yellow wire. In both cases, the meter should read approximately 25 to 30 volts at 3000 R.P.M. If these voltages are obtained, then the regulator is faulty and should be replaced.

11. If the proper voltages were not obtained in the previous paragraph, it is necessary to check the output of each magneto individually. To do this, remove the gas tank and disconnect the Red, White, and Yellow wires from each magneto where they plug into the mag to regulator harness.

12. Again using the AC voltmeter, measure the voltage from Red to White and from Red to Yellow of one of the mags. Repeat this test with the other magneto. It is necessary to replace the gas tank, or use an auxiliary fuel supply to perform this test. At 3000 R.P.M., you should obtain 13 to 15 volts AC in all four of these checks. If any one of these checks (Red to White or Red to Yellow on each mag) failed to produce 13 to 15 volts, then that magneto is faulty.

13. If both magnetos put out the required amount of voltage individually but you could not obtain the required voltage in paragraph 10 (both mags together) then the magnetos are running out of phase, or they are wired together incorrectly.

14. If the cylinders on your engine fire simultaneously that is 0 or 360 (the stock arrangement), then the wires from both magnetos should be connected as follows: Red to Red; White to White; Yellow to Yellow. See Fig. No.______.

15. If the cylinders on your engine fire 180 apart (the Yankee engine can be assembled to fire that way) then the magneto wires should be connected as follows: Red to Red; White to Yellow; Yellow to White. See Fig. No._____.

16. If your cylinders fire at neither 0 nor 180 apart, then one of two things have happened. Either someone has rebuilt the engine using a non-standard crankshaft coupler sprocket (available in 15, 30, 45, 75, 90, 105, and 150 on limited basis) or, a woodruff key has sheared inside the crankshaft coupler sprocket, allowing one of the crankshafts to twist out of alignment with the other. If the latter is the case, it will be necessary to disassemble the engine, separate the crankshafts and replace the woodruff key to realign the crankshafts.

17. If you have a non-standard coupler sprocket, the magneto lighting wires should be connected as follows to produce charging current.

Distance from T.D.C. of Right

  Lighting Wires from Each Mag

Cylinder to T.D.C. of Left Cylinder

  Connected Together


  Red to Red-White to White-Yellow to Yellow


  R to R W to W Y to Y


  R to R W to W Y to Y


  R to R W to Y Y to W


  R to R W to Y Y to W


  R to R W to W Y to Y


  R to R W to W Y to Y


  R to R W to W Y to Y


  R to R W to Y Y to W
NOTE: 30, 90, and 150 will work equally well wired either W to W, Y to Y, or W to Y, Y to W. Red must always connect to Red.    

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