Olympia Show - November 1919.
Stand 23 A.B.C.
As may be imagined, the alterations in the production model A. B.C. are only in detail, and we understand that, by the time the Show opens, the Sopwith Co. will be in a position to deliver a certain quantity of these machines to their agents.
So far as the engine is concerned, which, we may remind our readers, has a bore and stroke respectively of 69 x 54 mm. (400 c.c.), the chief alterations have been the fitting of larger diameter tappet rods and of altering the design of the tappet adjusters. The tappet adjusters now consist of hardened steel screws with hollow cone ends screwing into the tappet heads themselves and secured by lock nuts.
Tapered coil springs are now used for the valves instead of the volute variety which were fitted to the experimental model.
The lubrication has been considerably simplified, as the mechanical oil pump has been abandoned, and, instead, oil is fed from an automatic adjustable ; sight feed mounted on the tank, the oil being induced by suction from the crank case. In addition, an auxiliary hand-pump is also provided.
An innovation has been introduced in the shape of adopting the single-lever Claudel-Hobson carburetter which is coupled up to an exhaust heated induction pipe.
The 1920 models are equipped with a rear stand so placed that tlie machine can be jacked up with one hand, and a front stand, is also fitted.
Improvements have been made to the clutch by the addition of a very strong central spring, and four auxiliary springs placed at equal intervals round the clutch face.
Throughout the whole design, parts have been strengthened and improved in detail. One point we may mention is the fixing of the chain sprocket to tlie transverse gearshaft. The sprocket has a threaded boss and is keyed on to the shaft, the end of wliich is also threaded. A large nut is threaded on to the boss, and inside it is a flanged castellated nut screwed on to the shaft. Both are screwed on together and locked up tightly. When it is desired to withdraw the sprocket, the large nut is loosened and then the castellated flanged nut, and, if the latter is unscrewed, the sprocket is drawn off. This overcomes the diflicuity which is often encountered by many motor cyclists who wish to dismantle their chain sprockets, since with this simple xxx self-contained device no special tool such as is ordinarily used for this operation is necessary for the purpose.
It is interesting to note that the following gear ratios have been adopted for the solo A.B.C.: top 5.5 to 1, third 7.31 to 1, second 9.75 to 1, first 13.16 to 1, while the top gear ratio for sidecar outfits is 6 to 1.
A special housing cast on the top of the bevel casing accommodates a Lucas dynamo, which is driven by a spur wheel from the mainshaft in the gear box. A switchbox is carried on a metal case tixed on the top of the dynamo housing, while the accumulator is accommodated on the left-hand side of the frame behind the saddle tube. A Smith speedometer is also fitted.
The finish is particularly, good, a gun-metal effect being obtained by a special process, which includes stove enamelling. There are very few plated parts, and parts which are plated are heavily coppered before they receive the deposit of nickel.
Five-point connection is used to fix the sidecar to the motor bicycle, the sidecar axle being attached to the rear chain stay by means of a spherical joint. The springing of the sidecar has been carefully thought out; quarter-elliptic laminated springs serve to suspend tlie axle in harmony with the springing of the motor bicycle, while the quarter- elliptic springs form a continuation of the C springs of the sidecar body.
The MotorCycle, NOVEMBER 20th 1919. Page 579
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