AJS PORCUPINE
Fifty years ago, the AJS Porcupine was at the pointy end of motorcycle sport when it won the first-ever 500cc world title, but rule changes put a sharp end to its racing career
The story of the rare and exotic, world-title winning AJS twin
he AJS Porcupine is the rarest and most exotic of the many works racers entered by British factories in the history of world championship road racing. It’s also the most frustrating. The Porc’s position in posterity is assured, with works rider Les Graham winning the first-ever 500GP title on the AJS in 1949. What’s more, it remains to this day the only twin-cylinder bike ever to have won the 500cc title. Singles did it later, of course, and triples and fours, too – but never another twin.
The 500cc double-overhead-cam parallel-twin motor originated during the dying days of World War II as a supercharged design, designated E90S: ‘E’ for Experimental, ‘S’ for Supercharged, and ‘90’ because it was originally going to be raced under the Sunbeam badge, recalling the successful Tt-winning Model 90 works racer of the 1920s. AJS’S proprietors, AMC (Associated Motor Cycles, owned by the Collier brothers), had purchased the rundown Sunbeam firm from ICI in 1937, and were set on relaunching the marque post-war. But then rivals BSA made them an offer they couldn’t refuse for Sunbeam’s pedal cycle line in 1943 – and got the motorcycle marque thrown in, too. The GP racer was rebranded as an AJS.
Ironically, the E90S was the brainchild of legendary Norton race engineer Joe Craig, who joined AMC in 1939. Craig was planning a post-war replacement for the fast but unreliable supercharged V4 AJS, and originally dallied with an inline blown triple before (doubtless impressed by the Tt-winning performance of BMW’S Kompressor twins) settling in 1942 on a parallel-twin, near-horizontal supercharged layout, with 100° valve angles and hemispherical combustion chambers to optimise combustion.
SUPERCHARGING BAN
This layout would have allowed a gear-driven Roots-type blower to be positioned above the gearbox of the uni tconstruction engine which, like AJS’S own pre-war V4, would also have been water-cooled to combat the higher running temperatures of forced induction.
But the shock 1946 FIM ban on supercharging meant that designer Vic Webb – who had created the E90 largely in his spare time, with the help of Vincent design guru Phil Irving (then working for AMC) – had to hastily convert the design to an air-cooled, atmospheric induction format. This had domed pistons and a very different cylinder head with 90° valve angles plus distinctive spiked finning which gave rise to the ‘Porcupine’ nickname.
It initially delivered a meagre 29bhp in 1946 – perhaps leading Craig to return that year to Norton, to head up their race team! But by the time of the Porc’s debut in the 1947 Senior TT, it was 37bhp at 7600rpm – on low 70-octane pool petrol, necessitating a mere 7:1 compression ratio.
Despite a lack of testing, the untried E90 was promising in a race dominated by Craig’s Norton team. Les Graham was running fourth when he fell off, before remounting and pushing in with a thrown drive chain, to finish ninth. Jock West suffered clutch slip from the start, but after pitting for adjustments, lapped within three seconds of the fastest lap, en route to 12th.
That promise was confirmed by Ted Frend’s AJS
‘IT REMAINS TO THIS DAY THE ONLY TWINCYLINDER BIKE EVER TO HAVE WON THE 500cc WORLD TITLE’
victory in the 100-mile Hutchinson 100 at Dunholme later that year, and West’s third place in the Ulster GP.
SPEED RECORDS AND GP WINS
In 1948 development continued, with West third this time at Assen, then second the following weekend in the Belgian GP, where the Porcupine’s undoubted turn of speed showed to good effect on the ultra-fast Spa-francorchamps circuit.
All three AJS riders had retired from the Senior TT, but Graham finished third in the Ulster GP before a works Porcupine sped to a total of 18 world records at Montlhéry in November, a good omen for the introduction of the first-ever motorcycle world championships the next year.
This six-race series was crowned with success for the AMC works team, with Les Graham winning the riders’ title, and AJS the manufacturers’ crown. This came after a poor start to the season, when Graham led the Senior TT for almost the entire race, before once again breaking down on the run to the flag, this time with a broken magneto drive. He pushed in tenth from Hilberry.
Graham took victory in the Swiss GP on Berne’s gruelling Bremgarten circuit, to record the twin’s first GP win, a success he repeated later in the season in the Ulster GP, with Doran and West fourth and fifth.
In the meantime, Graham had finished in second place, beaten by Pagani’s works Gilera four at Assen, before retiring with a split fuel tank at Spa, in a Belgian GP won by AJS team-mate Bill Doran.
Even before the end-of-season Italian GP at Monza, in which Doran finished third (with only a rider’s best three results counting in the final points table), Graham had done enough to win the inaugural 500cc World title.
LOSING ITS COMPETITIVE EDGE
For 1950, the AJS 500 twins got detail improvements under the direction of project leader Matt Wright, whose influence had been a crucial role in winning the world title. This included a larger fuel tank and a streamlined seat, but the ignition problems which were a constant Achilles heel were not resolved. Combined with troublesome carburation, eventually traced to fuel starvation, these were the cause of many Porcupine retirements. Even worse, the more assured handling of the new Featherbed Norton frame, coupled with the better top speed of the Gilera fours, meant the AJS was now secondbest in both these areas. This wasn’t helped by the refusal of AMC managers to allow anything other than their own ineffective Teledraulic forks and Jampot shocks to be used, for financial reasons.
Graham finally finished a Senior TT – but only in fourth, behind a trio of Nortons led by Geoff Duke. Graham also retired in Belgium where Ted Frend averaged 100.39mph to finish third on his AJS behind two Gileras.
Like all other British works teams, AJS and Norton ran into big problems with their Dunlops at Assen, where Graham led before retiring with a thrown tread, due to a combination of high speeds and equally high temperatures.
But although Graham repeated his Swiss GP victory, this time in Geneva, and finished second to Duke’s Norton in the Ulster GP with West fifth, third was the best the
‘A PORCUPINE SPED TO 18 WORLD RECORDS AT MONTLHÉRY IN 1948’
defending champion could achieve in the final best-four points table, behind Gilera’s Umberto Masetti and Duke. Disillusioned, he switched to the new MV Agusta team, whose Gilera-inspired four held more promise.
PORCUPINE LOSES ITS SPIKES
Wright’s development team revamped the AJS for the ’51 season, reducing weight and introducing chain magneto drive, solving the issue of fractured armature shafts; wetsump lubrication which did away with an oil tank; a shorter wheelbase for the tubular steel duplex frame; 19in wheels rather than the previous 21in; a new design of fuel tank; and separate cylinder heads with conventional finning – in spite of which, the ‘Porcupine’ tag still stuck.
With Irish rider Reg Armstrong joining Bill Doran, the AJS was now more reliable, allowing Doran to claim second place in the Senior TT and again in the French GP at Albi, with Armstrong second in Switzerland. But due to ongoing carburation problems, it failed to win a race that year, and only managed fourth for Doran in the eight-round world championship points table, with Armstrong sixth. The AMC board commissioned a complete redesign for 1952, with R&D boss Ike Hatch producing a revamped engine with cylinders now at 45° from horizontal (while retaining the same essential internal layout), fitted as a semi-stressed member in an open-cradle frame.
This new bike, dubbed the E95, had a dream debut. It finished 1-2 in the season-opening Swiss GP in Berne, with new team member Jack Brett winning the race ahead of Doran, and AMC’S new Kiwi recruit Rod Coleman placing fifth. But it was all downhill from there, with Doran and Brett retiring from a Senior TT won by Norton’s latest acquisition Reg Armstrong, ahead of MV Agusta-mounted
Les Graham – both former AJS team riders! Coleman was fourth at the TT, with Bill Lomas, who he said he hated riding the Porcupine, finishing fifth.
“When it was banked over, one cylinder would cut out intermittently, then chime in hard again,” he recalled with a grimace. “One place, the second pot came in so viciously, I rode 50 yards up the road sideways! I wanted to pull in, but I didn’t think the management would like that, so I decided to over-rev the engine till it blew up. We were told not to rev it above 7000rpm, but I took it to over 8000rpm – and it survived, so I ended up fifth. Bloody thing!”
ON CLADY’S SEVEN-MILE STRAIGHT
Coleman was also fifth at Assen, and again at Spa, while after a disastrous German GP at Solitude in which all three AJS twins retired, the promising Kiwi took second
ABOVE: Bill Lomas enters Parliament Square en route to fifth place in the 1952 Senior TT on the redesigned AJS Porcupine
place in the Ulster GP, in the last-ever run on the Clady circuit with its punishing seven-mile straight.
But he was fortunate to do so – for AJS colleague Jack Brett had rounded the last turn, less than a mile from the finish, securely in the lead on his Porcupine, only to have its drive chain jump the sprocket. Forced to push in to finish fourth, he was also passed in doing so by eventual winner Cromie Mccandless, having a one-off ride on a works Gilera four. With Brett’s seventh place being the best that the trio of AJS riders could manage at Monza, AMC management opted to withdraw from the final GP of the season in Barcelona.
The 1953 season was no better, with no AJS rider once finishing on the rostrum in the eight-race series, so the bike was completely revamped for the following year by AMC’S pragmatic, effective new development engineer, Jack Williams (father of later John Player Norton star Peter).
With 54bhp being the most the engine could be persuaded to deliver reliably, most attention was paid to the cycle parts – a new lower frame and massive 6.5-gallon fuel tank were draped over the engine to reduce the frontal area of rider and machine. The retention of the four-speed Burman gearbox at a time when the competition now had five-speeders was a further handicap.
Coleman was joined for the season by Derek Farrant and another rising star, Scotsman Bob Mcintyre, but with Duke now riding for Gilera, whose fast bikes now handled properly thanks to his Featherbed-inspired input, the Porcupine was not only still outpaced but also now outhandled. Coleman only got the better of the works Gileras on one occasion, by winning the non-championship Swedish GP at Hedemora in what would be the Porcupine’s final race in factory guise. At the end of the season, the AMC board pulled out of GP racing officially.
The AJS Porcupine’s place in the history of competitive motorcycling is perhaps best summarised by the period racing guru Vic Willoughby, who wrote: ‘Notwithstanding spasmodic success for a few years following Les Graham’s championship, the Porcupine never really recovered from the attempted transition from the comparatively lowrevving, high-boost machine it was originally intended to be, to the high-revver, with much wilder valve timing, that the post-war formula demanded.”
For just a single year, in 1949, the slightly greater power output of a higher-revving twin compared to a single, coupled with the slightly better handling of a low-slung parallel twin compared to an inline four, proved the best of both worlds, rather than a flawed compromise that eventually delivered neither one thing nor the other.
‘WHEN IT WAS BANKED OVER, ONE CYLINDER WOULD CUT OUT INTERMITTENTLY, THEN CHIME IN HARD AGAIN’