AJS Porcupine

The AJS 500 cc Porcupine was a British racing motorcycle built by Associated Motor Cycles (AMC), which débuted in 1945 with a horizontal-engine designated E90S.

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.

[5] 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.

The loss of the supercharger meant that the design was compromised, lacking sufficient flywheel effect, which caused problems with magneto failure.

[7] The 1947 model engine was mostly made of alloy, but, as an experiment, the head was cast in silver for increased thermal efficiency.

[4] Team Obsolete have restored a 1954 AJS Porcupine E95, using an ex-Tom Arter MKII motor, which features a unique Jack Williams built up roller bearing crankshaft.