BSA Motorcycles 1950s

Today in Motorcycle History

Removing the sludge trap

As most A10 enthusiasts know, cleaning of the sludge trap is a must when rebuilding the engine to assure that oil can flow freely through the engine. Removal of the sludge trap can be quite challenging and I have tried to summarize the tricks I had to use to remove my sludge trap. Without these tricks (which were passed on to me by others), removal of this sludge trap could take a great deal of time.

To get at the sludge trap, the crankshaft should be removed from the engine crankcases. To get the crankcases apart, you must remove all bolts along the edge of the cases including the one inside the casings near the rocker arms. You must also remember to take off the scavenge cover plate with oil filter at the base of the engine. The cases will then separate leaving behind the crankshaft attached to one side of the crankcase by the crankshaft timing pinion.

To remove the crankshaft from this timing pinion, the oil pump and right hand threaded worm drive must be simultaneously removed (to prevent damage to the oil pump) and the timing pinion pulled or driven out (with a special BSA pinion extractor [gear puller] tool #61-3256 or everyday mallet). In my case, I went the cheap route (i.e., without a BSA pinion extractor) and easily drove the crankshaft off the sprocket. Note: To prevent damage to the crankshaft threads, I put the reverse threaded nut back on flush with the end of crankshaft prior to driving the crankshaft off and used a block of wood to cushion blows to the crankshaft.

The sludge trap is held in place by two plugs at each end of the crankshaft (crankshaft oil hole end plugs). These end plugs were punched at the factory around their circumference in order to purposefully damage threads and prevent backout. This punching procedure makes removal of the end plugs nearly impossible, even using an impact driver. One technique I have successfully used to remove the end plugs involves using a 5/32" drill bit (suitable for drilling metal) to drill at the center point of the punch indentation. The depth of drilling should be controlled such that no drilling occurs beyond the depth of the threads damaged by the punch mark.

The previously mentioned technique removes the damaged portion of the threads and should allow for the removal of the end plug, although sometimes it is necessary to obtain additional torque to get the end plug to unscrew out of the crankcase. To obtain this extra torque, drill into the center of the end plug with a 5/16" drill bit (again with a bit suitable for drilling metal). A 5/16" allen wrench should then be obtained and L-bend angle cut off such that the allen wrench can be driven right into the drilled hole in the center of end plug. A wrench can then be used to turn the allen wrench thereby allowing for much more leverage then a screw driver could have applied (Side Note: this trick was passed on to me by Brian Pollitt of the UK BSA Owners Club).

The sludge trap is basically a hollow tube with a slight expansion in diameter along a section on one side. Three holes are present in the tube, two for oil circulation and one for securing the sludge trap with the radial flywheel fixing bolt (shown in previous figure). Before this sludge trap can be removed this flywheel fixing bolt nearest the sludge trap along the outer circumference of the flywheel must be removed to release the sludge trap. (Side Note: The flywheel bolt can also be difficult to remove. In my case, I had to put the crankcase in a table vise, and use a car jack to turn my wrench on the flywheel bolt to get the darn thing off.) On my BSA, the end plugs present on the opposite sides of the flywheel were not identical (although all my spares lists only document part number (67-1211) for both sides. The end plug not listed in the spares list had a smaller diameter projection on the inside that fit into the wider end of the sludge trap (whereas the opposite end plug was flat on both ends (aside from the screw driver slot). Based on input from others, the end plug (67-1211) listed in the parts list can be used without problem on both ends of the crankshaft; however, the "correctly" designed end plug can be obtained from SRM. Additionally, when replacing these plugs, the A10 owner may want to consider hexagon allen type end plugs described in the improved parts for the A10 section of this webpage.

When installing the new end plugs - do NOT allow the plugs to become recessed. They should be installed flush with the surface to allow free oil flow.

Alternative method for Removing End Plugs

Following is an alternative, less destructive technique for getting to your sludge trap passed on to me by John Healy - Triumph International Owners Club. The technique I described above can cause irreparable damage. Many premature crank failures can be traced directly to centering on the punch mark and drilling the crankshaft to remove the oil way end plugs.

To prevent this, center punch the PLUG itself, just inside of the factory mark, and "worry" the drill toward the factory punch mark. Drill only until you just remove the "pinched" metal that is holding the plug. Little if any metal should be removed from the crankshaft itself. This leaves the crankshaft unscared and ready for many happy miles.

An alternative to my advice about drilling a single hole and inserting a allen wrench: You can drill two more holes along the the screw driver slot and drive in a large "screw driver blade" 1/2" socket. Even the tightest plug which was loctited in place is easily removed. Use an 1/2" drive air wrench on the screw driver adaptor, and you will wonder what all of the fuss over these plugs was about.

When repunching, place the center punch on the new plug and "pinch" the metal into the old punch mark on the flywheel. This spares the flywheel from any damage.

Not matter how you remove the plug it is important to spare the crankshaft from any damage!!!