AJS Porcupine

The AJS 500 cc Porcupine E90S was a British racing motorcycle built by Associated Motor Cycles (AMC), which débuted in 1945. AMC produced the AJS and Matchless brands at the time.

The motorcycle was originally designed by AJS to be supercharged, as were a number of pre-war racing bikes, but the FICM banned supercharging in 1946. The motor was then worked on to allow it to perform without a supercharger. Jock West first rode the machine at the 1947 Isle of Man TT where he experienced teething problems relegating him to a 15th place although, he recorded the third fastest lap time of the race.Leslie Graham then rode the bike to victory in the inaugural 1949 500cc world championship. This was the only World Championship win for AJS. Despite this victory, the bike is often cited as unreliable, and not living up to its promise.

The E90S Porcupine engine was a unit construction, aluminium alloy, 500 cc, DOHC twin, with horizontal cylinders and heads, to give the bike a low centre of gravity. A later version of this motor was named the E95, re-engineered to have its cylinders inclined at 45 degrees for better cooling and easier carburettor installation, and is claimed to have produced 55 bhp @ 7600 rpm

The gear drive for the camshafts was on the right of the motor, while the gear primary drive was on the left. The geared primary drive meant that the motor ran “backwards”. The cam gear drive also drove a jackshaft at the rear of the cylinders, which drove an oil pump, a fuel pump, and (via a chain drive) a Lucas magneto. The four-speed gearbox output was on the right.

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Wikipedia