AJS Porcupine

The AJS 500 cc Porcupine was designed to be supercharged, as were a number of pre-war racing bikes, and was announced in 1945, but the FICM banned supercharging in 1946.[1] The Porcupine was preceded by the water cooled, supercharged 1935 - 1939 AJS V4. The motor was then worked on to allow it to perform without a supercharger, and in this form Leslie Graham rode it to victory in the first GP World Championship of 1949.[2] This was the first and only World Championship win for AJS. Despite this victory, the bike is often cited as unreliable, and not living up to its promise. The Porcupine motor was a unit construction, aluminium alloy, 500 cc, DOHC twin, with the cylinders and four valve heads inclined forwards at an angle of 45 degrees, to give the bike a low centre of gravity. It 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. It had rubber mounted twin GP carburettors, inclined at 49 degrees, with an unusual float tank system used rather than float bowls. Plain bearings were used for the big end bearings and the centre main bearings. The outer main bearings were rollers. One problem cited for the engine is the use of non parallel valves with conventional rockers. The 1947 model engine was mostly made of alloy, but, as an experiment, the head was cast in silver for increased thermal efficiency. Due to the softness of silver, it had to be alloyed to make it hard enough for racing use. By the time this was achieved the thermal efficiency gains were lost, and the experiment was abandoned. The Porcupine used ?Jam-pot? shocks and Teledraulic race forks. The E90 model had an open frame. The E95, introduced in 1953, had a loop type frame with the motor mounted lower. Only four E95 Porcupines were built. Team Obsolete have restored a 1954 AJS Porcupine E95, using an ex-Tommy Arter MKII motor, which features a unique Jack Williams built up roller bearing crankshaft. They use it for exhibition and historic racing. Tommy Arter put a complete 1954 E95 AJS Porcupine up for auction, and it sold for $228,620