AJS E95 Porcupine

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 FIM 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.

E95 Porcupine engine

The E90S Porcupine motor 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 carburetor 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.

As originally designed, the E90S was to be supercharged, with the blower mounted above the gearbox, and driven by the clutch. The loss of the supercharger meant that the design was compromised, lacking sufficient flywheel effect, which caused problems with magneto failure. The main initial change was to reduce the valve angle to 90 degrees for a more compact combustion chamber.

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. There is dispute as to whether the silver cylinder head went beyond feasibility-study stage.
The Frame

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.

Bonhams background:

Introduced in 1952, the E95 engine had its cylinders tilted upwards at 45 degrees, an arrangement that permitted a shorter wheelbase. The new motor layout featured a more robust crankshaft, and improved cylinder head architecture. Its distinctive spike fins had gone, but the 'Porcupine name stuck. The E95 enjoyed a dream debut, new recruit Jack Brett and Bill Doran finishing 1st and 2nd respectively at the season-opening Swiss Grand Prix, with New Zealand star Rod Coleman in 5th place.
 

For 1954, the final year of competition, the E95 Porcupine (and works 'triple-knocker' 7R3 350 single) gained the new pannier-style fuel tanks which extended down on either side of the engine, thus lowering the center of gravity and affording a measure of streamlining at the same time. An AC fuel pump was used to raise fuel to the carburetors, a delivery system that involved mechanics standing the bike on its rear wheel to prime the internal header tank for starting! Jack Williams took over the race team that year and the result of his development was a much smoother engine, which now produced a maximum of 54bhp at 7,800rpm. Bob McIntyre, Derek Farrant and Rod Coleman were the riders, the latter providing the Porcupine with its best international results of the season, placing 2nd in Ulster and winning the Swedish Grand Prix. Other riders to swing a leg over the Porcupine during its short career include Bill Lomas, Robin Sherry and Reg Armstrong.

Sadly, 1954 would prove to be the Porcupine's swansong year. With the death of AMC founder Charlie Collier, AJS withdrew from direct involvement in Grand Prix racing at the season's end, never to return. But the record books tell the story: between 1949 and 1954, Porcupines finished 24 races with five wins, seven 2nd places and one World Championship. In total, only four complete E90 and four E95 machines were built. Only one E90 survives. With the exception of the E95 acquired later by privateer Tom Arter, they were raced exclusively by the works team and never offered for public sale. Fortunately, all four E95s survive today. Two are in a Chartered Museum. One other is in private hands, owned by Team Obsolete.