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British Motorcycles

Abingdon 624cc Big Single 1921

NOVEMBER 24th, 1921.

A Big Single Abingdon.

A 4 1/4 h.p. Engine for Heavy Passenger Work.

UNDOUBTEDLY one of the features of the Show will be the increase in the number of big singles. Quite one of the most interesting of these is the 4 1/4 h.p. Abingdon King Dick (85x110 mm. = 624 c.c.). This machine has been designed primarily for heavy passenger work and not essentially for high speeds ; thus, we find that simplicity and sturdiness are the main characteristics of the new engine. Side-by-side valves are employed, operated by a single cam, the inlet having a direct lift through a tappet housed in a long cast iron guide, and the exhaust being actuated through a bell crank rocker. There are, therefore, only two gear wheels in the timing case, and these are exceptionally wide so as to ensure quiet running and long life.

Lubrication is effected on the principle introduced by Mr. Blumfield many years ago - that is to say, that oil is led to a large plain bearing on the timing side, whence it is forced inwards by the action of the crankshaft in conjunction with a spirally grooved bearing. The oil escaping in proximity to the flywheel is caught in a thrower ring and flung by centrifugal force to the big end. This big end, by the way, is a bronze bush of exceptional area.

The driving side of the crankshaft is carried in a very large diameter Skefko bearing, the outer race of which is housed in a steel ring and not in the aluminium of the crank case. A flange on this housing is machined so as to form a double face joint for the oil-tight chain case, and a felt oil gland is provided behind the bearing.

Connecting Rod Design.

An I section connecting rod is split at the small end, and when tightened up grips the centre of a very large diameter hollow gudgeon pin. The piston is of oast iron, having three top rings, the lower ring acting as a sora.per, and oil return holes being provided directly to the gudgeon pin bosses. Floating in the piston bosses, the gudgeon pin is not liable to cause distortion ; nevertheless, the sides of the piston are relieved, and oil grooves are provided on the bearing slippers.

Designed for Cool Running.

There is plenty of metal in the cylinder casting, which is well laid out as regards cooling, and the circumferential ribs are joined front and rear to prevent ringing. Incidentally, there are wide air spaces between both ports and the cylinder.

From a short road test, we are able to state that the engine is admirably suited to the purpose for which it is designed, and the heavy flywheels enable it to pull slowly without snatch.

Fitted with a three-speed gear box, clutch, kick-starter, and all chain drive, the frame is a powerful piece of construction, the chain stay lugs in particular being very massive, while the large ball bearing hubs are rendered oil-tight and dustproof by a simple form of packing gland which has proved most effective in service.

Caption All-chain drive is used on the 4 1/4 h.p. Abingdon King Dick, which is designed specially for sidecar work. Quickly detachable wheels are fitted.

Caption A newly-designed Abingdon King Dick big single of 624 c.c. Observe distinctive arrangement of cooling fins, which do not extend round the inlet valve pocket. 

Sources: The MotorCycle



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