AJS "Porcupine "

AJS "Porcupine " 1947

1947 A.J.S. "PORCUPINE". Probably the unluckiest design ever to emanate from the Woolwich A.M.C. factory as far as the T.T. races were concerned was the racing twin announced in May 1947 and, because of its peculiar cylinder-head finning, quickly dubbed the "Porcupine". In its eight years of development it scored successes everywhere—except in the T.T. Few racegoers cannot have heard of the cruel luck that befell the late Les Graham who, when leading the 1949 "Senior" very comfortably, had a magneto armature spindle shear when almost in sight of the finish.

The engine, designed with a four-speed gearbox in unit, had its cylinders lying almost horizontal. Primary drive was by gears (the engine ran "backWards") and the entire unit had originally been intended to include a supercharger mounted atop the gearbox. Twin overhead camshafts were driven by a gear train carried in a Y-shaped case on the offside of the unit. A full duplex cradle frame, with swinging-fork rear suspension, had the by-then-famous "Teledraulic" front fork similar to that pioneered during the war on W.D. 350 c.c. Matchless machines. Both front and rear suspension had 3 in. of movement and the rear units were of the oil and air type.

In their first T.T. the A.J.S. twins were too new to do more than be in a "useful"' position if anything went wrong with the Norton stars. Nonetheless, Les Graham was only 3 m.p.h. down in sixth place at the end of six laps—his chain came off at Governors Bridge on the last lap and dropped him to ninth finishing position after pushing in. "Jock" West had battled with a slipping clutch on the opening lap and this took him 84 minutes, but by cracking round and making second-fastest lap of the race he finally worked up to finish fourteenth. If that clutch had been O.K. at the start. . .

SPECIFICATION
Engine: parallel-twin 500 c.c. d.o.h.c; light-alloy cylinders and cylinder-heads; gear drive to camshafts.
Ignition: magneto.
Transmission: spur gears to four-speed gearbox in unit
with engine; final drive by chain. Frame: duplex cradle with pivoting-fork rear suspension. Forks: A.M.C. "Teledraulic" telescopic.

AJS "PORCUPINE" 1954

1954 A.J.S. "PORCUPINE". A lineal descendant of the original I_T'Porcupine", by 1954 A.J.S.'s racing
500 c.c. twin had been considerably revamped during seven years' steady development.
Gone were the original spike fins on the cylinder-heads—though the name "Porcupine" stuck.

The cylinders were raised to an angle of 450, which gave better cooling of the cylinder-heads in the exhaust port area, where, previously, they had been shielded by the cam-box. A large sump lay between the exhaust pipes and carried seven pints of lubricant— weight low down generally helps handling.

A major innovation was the employment of weir-type carburetters in which no float chambers of the normal type were used. Instead a small header tank was formed in the rear of the petrol tank and this fed a small chamber for each carburetter, an overflow pipe letting excess petrol flow to a container just astern of the oil sump. From there petrol was pumped back up to the header tank by a pump driven from the magneto driving cross-shaft.
Drive to the overhead camshafts, and from engine shaft to gearbox, was still by gears, and the unit retained the plain centre main and big-end bearings introduced in the original design.
In 1954 the value of streamlining was just beginning to be appreciated, although there was still a lot of doubt as to whether the additional weight was worth the gain in speed.

The A.J.S. designer got around this, in a very neat way, by making the fuel tank a very low-slung affair, with deep recesses for the rider's knees. This enabled 6\ gallons of fuel to be carried, put a lot of the fuel load weight low down and also gave a few extra m.p.h. because of the streamlining effect.
At the end of its development, the 1954 engine was developing 54 b.h.p. at 7,500 r.p.m.—very good, but not enough to catch the Italian fours.

SPECIFICATION
Engine: parallel-twin 500 c.c. d.o.h.c; light-alloy cylinders and cylinder-heads; gear train drive to camshafts.
Ignition: magneto.
Transmission: spur gears to four-speed gearbox in unit
with engine; final drive by chain. Frame: duplex cradle with pivoting-fork rear suspension. Forks: A.M.C. "Teledraulic" telescopic.

History of the AJS Porcupine  by Larry from Team Obsolete in Brooklyn, New York.

1954 AJS 497cc E95 Porcupine " Racing Motorcycle" Frame no. F3, Motor No E2 / 54

Britain's first success in the modern era's Grand Prix World Championships was achieved by a marque with an illustrious racing history - AJS. And the machine that carried Les Graham to his, and AJS', first and only World Championship in 1949 was, of course, the legendary Porcupine. To this day the Porcupine remains the only twin-cylinder motorcycle to have won the 500cc World Championship. The 1954 AJS 500 c.c. E-95 Porcupine represents the final development of the most exotic, innovative, and graceful British Grand Prix racing motorcycle ever made. New for 1954, its final year of competition, the unique low handmade alloy “pannier” fuel tank wraps around the motor. The magnesium camboxes protrude out from under the front of the tank, capturing the cooling air.

Only four E-95‟s were built. They first appeared at the 1952 Isle of Man TT. Development continued, eventually under the genius of race shop head Jack Williams. For the 1954 Season he introduced the pannier fuel tank (which required a fuel pump) with the matching lowered chassis.

Unlike the rival works Nortons, the Porcupine shares little with the production machines sold to the public. The motor and gearbox are unit construction with gear primary drive. Power is transmitted through what may be the most beautiful exposed clutch ever seen. The long graceful cast alloy underslung oil tank is a full gallon in capacity. The twin overhead camshafts are driven by a train of gears that also drive the special aircraft magneto and the high capacity oil pump. Extensive use is made of lightweight ELECKTRON castings.


Conceived towards the end of WW2, the Porcupine was originally designed to be run either with or without forced induction. Supercharged multi-cylinder engines had begun to threaten the single's supremacy towards the end of the 1930s and indeed, AJS themselves went down this road with their fearsome water-cooled V4. Fast yet difficult to handle, the latter had demonstrated that horsepower bought at the expense of excess bulk and weight was not the answer, so the thoughts of designer Vic Webb turned to a twin. Laying the cylinders almost horizontally with their heads facing forwards ensured adequate cooling and a low centre of gravity while at the same time providing room, if required, for a blower above the gearbox. When the FIM banned supercharging at the end of 1946, AJS was ready with new cylinder heads designed for normal aspiration!

Typed E90 but dubbed 'Porcupine' by the motorcycling press because of its distinctive spiked 'head finning, AJS' new challenger debuted at the 1947 Isle of Man TT in the hands of Les Graham and Jock West, the pair finishing 9 th and 14 th respectively after encountering a variety of minor problems. By way of consolation, West's best lap was only three seconds down on the fastest and showed that the bike had promise. The Porcupine's first race victory was achieved later that year by Ted Frend at the Hutchinson 100. Development continued throughout 1948, with a number of Grand Prix podium finishes and 18 world speed records among the season's highlights.

The inaugural 500cc World Championship of 1949 consisted of six races, with victory going to Les Graham at the Swiss and Ulster Grands Prix. Bill Doran won the Belgian GP to assure AJS of the manufacturers' title, while Graham's two wins were enough to take the riders‟ championship from Gilera's Nello Pagani.

Many years later, AJS works rider Ted Frend - the first rider to win on the bike - recalled that carburetion had been the Porcupine's biggest problem. Over the years several different induction arrangements were tried. Eventually, the 1954 pannier fuel tank and fuel pump solved this problem. The E90 was also bedevilled by failure of the gear driven magneto shafts - the cause of Graham's retirement from the lead of the '49 Senior TT just when two minutes from the finish. The problem was solved when chain drive for the magneto was adopted on the revised E95 engine. 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 1 st and 2 nd respectively at the season-opening Swiss Grand Prix, with New Zealand star Rod Coleman in 5 th place.

Another new addition to the AJS team for '52, Coleman had first been given an E90 to try at the '51 Ulster GP and followed that up with a strong showing at the Grand Prix Des Nations at Monza. "In the race it was quite definitely faster than the Nortons and I had little problem getting past Geoff (Duke) and Ken (Kavanagh) with just three Gileras only a short distance ahead," Rod recalls in his book, The Colemans. I did get with them and found again that the Porcupine was just as fast as the Gileras but was down a little on acceleration from the slower corners, but not by much. I was just beginning to think I had every chance of second place behind Milani when the motor stopped." The cause? Yet another magneto shaft failure.

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 centre 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 2 nd 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 2 nd places and one World Championship. In total, only four complete E90 and four E95 machines were built. Only one E-90 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.  On display at the Museum for decades, F3 was mechanically restored in the USA between 2000 and 2004 by New York-based Team Obsolete - luckily escaping the Museum‟s disastrous fire of 2003.

Source returnofthecaferacers.com