Letters from readers, April 1943

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Sir,

Concerning H. G. Hanmer’s queries, I think that I can supply details of at least two of the “famous motor-cycles” he mentions.

The big twin A.J.S. he refers to was built in 1930 for records; it was a 50 deg. twin of 79 mm. bore by 101 mm. stroke (just under 1,000 c.c.), having chain-driven overhead camshafts operating inclined valves in aluminium heads with cast-iron seatings; the cylinder barrels were steel with hardened bores. Two carburetters were fitted, each facing to the rear of the machine, whilst the exhaust ports faced forwards.

This massive unit was mounted in a robust cradle frame with a single top tube of no less than 2.5 in. diameter, the cradle tubes being 1,3/8 in. Transmission was by chains via a Sturmey-Archer box, top being 3.2 to 1. I do not remember the machine coming up to expectations, although it went very quickly at Southport, ridden by Joe Wright, but not quickly enough!

The late C. B. Bickell’s blown “square-four” Ariel was a mount of great technical interest, being a departure from the typical English “pneumatic drill” type. It was originally a 1933 600-c.c. demonstration model. Bickell fitted a smaller block and pistons to bring it within the 500-c.c. class and slightly lowered the compression ratio. The crankcase assembly was not altered. To mount the Powerplus blower the saddle tube was removed and two 1/4-in. steel plates joined the tank rail to the cradle frame; between these, over the gearbox the blower was mounted and driven by chain from a sprocket mounted behind the clutch. The carburetter was fitted between the rear wheel and the 3-speed Burman box, below the supercharger. The induction pipe ran round the near side of the block to the point where the normal atmospheric carburetter was placed. A very large and beautiful tank was used and the saddle mounted over the rear wheel.

Bickell’s machine was capable of lapping consistently at over 100 m.p.h. and had a most awe-inspiring note. I consider it an astonishing performance for a practically standard machine with the addition of a supercharger.

May I point out, to the same correspondent, that Dr. Beaver’s Vauxhall did not stop blown for long; it used one of Marshall’s experimental centrifugal blowers, which were never fully developed.

I am, Yours etc.,

H. L. Biggs.

Enfield, Middlesex.