Racing history

The motorcycle was originally designed by AJS

AJS

AJS was the name used for cars and motorcycles made by the Wolverhampton, England, company A. J. Stevens & Co. Ltd, from 1909 to 1931, by then holding 117 motorcycle world records, and after the firm was sold the name continued to be used by Matchless, Associated Motorcycles and Norton-Villiers on...

 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

Jock West

John Milns "Jock" West, MBE was a Grand Prix motorcycle racer from Great Britain.-Motorcycle career:West was born in Belvedere, Kent to an English father and a Scottish mother. He initially concentrated on grasstrack racing on an Ariel motorcycle and, was successful enough that the Ariel factory...

 first rode the machine at the 1947 Isle of Man TT

1947 Isle of Man TT

After an eight year absence the 1947 Isle of Man Tourist Trophy was the first race festival since 1939 due to the interruption of World War II. With the restart of racing the ACU decided to add three Clubman class races for production machines and introduced these races for Lightweight, Junior and...

 where he experienced teething problems relegating him to a 15th place although, he recorded the third fastest lap time of the race. Leslie Graham

Leslie Graham

For the English footballer and manager see Leslie Graham Robert Leslie Graham DFC was a British motorcycle road racer who competed in the 1930s and 1940s...

 then rode the bike to victory in the inaugural 1949

1949 Grand Prix motorcycle racing season

The 1949 Grand Prix motorcycle racing season was the inaugural F.I.M. Road Racing World Championship Grand Prix season. The season consisted of six Grand Prix races in five classes: 500cc, 350cc, 250cc, 125cc and Sidecars 600cc...

 FIM

Fédération Internationale de Motocyclisme

The Fédération Internationale de Motocyclisme is the governing body of motorcycle racing. It represents 103 national motorcycle federations that are divided into six regional continental unions....

 500cc world championship

Grand Prix motorcycle racing

Road Racing World Championship Grand Prix is the premier championship of motorcycle road racing currently divided into three distinct classes: 125cc, Moto2 and MotoGP. The 125cc class uses a two-stroke engine while Moto2 and MotoGP use four-stroke engines. In 2010 the 250cc two-stroke was replaced...

. 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 Motor

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 carburettor installation, and is claimed to have produced 55 bhp @ 7600 rpm

The gear drive for the camshaft

Camshaft

A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...

s 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

Jackshaft

A jackshaft is a device for turning the wheels of a locomotive. It is essentially an axle with no wheels. Each end of the jackshaft has a crank pin and a counterweight. The driving wheels are then connected by side rods. The name may come from a combination of "jack," a slang term for a locomotive,...

 at the rear of the cylinders, which drove an oil pump, a fuel pump

Fuel pump

A fuel pump is a frequently essential component on a car or other internal combustion engined device. Many engines do not require any fuel pump at all, requiring only gravity to feed fuel from the fuel tank through a line or hose to the engine...

, and (via a chain drive

Chain drive

Chain drive is a way of transmitting mechanical power from one place to another. It is often used to convey power to the wheels of a vehicle, particularly bicycles and motorcycles...

) a Lucas magneto

Magneto

A magneto is a type of electrical generator.Magneto may also refer to:* Magneto , permanent magnetic alternating current rotary generator* ignition magneto, magnetos on internal combustion engines...

. 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 fly-wheel 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.

The AJS Porcupine Today

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. They use it for exhibition and historic racing.

Tom Arter put a complete 1954 E95 AJS Porcupine up for auction, and it sold for $228,620.