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Velocette Supercharged 500 1939

1939 VELOCETTE SUPERCHARGED 500. The war can be I-1 blamed for a lot of things, and it certainly caused the premature
dropping of development on one of the most interesting racers ever to see the T.T. course. This was the 500 c.c. supercharged Velocette, which appeared for only one practice period in the 1939 T.T. The war started in September, so the machine was stored away for the duration. After the war there was a ban on "blowers" in international racing, so the "Roarer", as the model was affectionately known at the works, was never raced again.

The machine was completely different from any racer ever to appear before it. It was a parallel-twin which was virtually two 250 c.c. singles mounted side by side, with their crankshafts parallel to each other and geared together; this meant that, as the two halves of the engine obviously revolved in opposite directions, they achieved almost perfect balance. Both crankshafts were extended rearwards (they were in line with the frame), and the one on the near-side drove the gearbox built in unit with the motor. The other crankshaft extension drove the supercharger, which was mounted alongside the gearbox. Final drive was by a shaft and bevel gear in the rear hub.

The engine was originally designed for liquid cooling, and so the exhaust ports could safely be faced rearwards. To get the machine complete in time for the T.T., air-cooled heads and barrels, with deep "square" finning reminiscent of the KTT, were made and fitted but, surprisingly, the rearward-facing exhaust ports were retained.

A special frame was employed, with swinging-fork rear suspension of the type used so successfully on the 350 c.c. Mk. VIII KTT, and front forks were also KTT-style Webb girders—but both wheels had very special full-width alloy hubs. *
The machine did not shine in its one practice session and was taken back to the factory for further development. If the war hadn't . . .

If looks could win races this machine should have beaten them all; the deep Velocet tank, massive engine unit and small forks gave the model a cobby appearance. Note ti shaft drive and, in close-up, the supercharger driven from the "right" crankshaft. Tl magneto and rev-counter drive are just behind the barrels.

SPECIFICATION
Engine: parallel twin 500 c.c. o.h.c; two-geared crankshafts; drive to camshafts by shaft and bevels. Ignition: magneto.
Transmission: shaft drive via four-speed gearbox bu
in unit with the engine. Frame: duplex cradle with pivoting-fork rear suspension Forks: Webb T.T. girders with single compre:
spring and friction dampers.