Our motorcycling legend, Bruce Cox, returns with another fascinating story from the world of historic bikes.
A “Porcupine” Without the Spikes!
The original AJS 500cc Grand Prix contender made history in 1949 by taking Les Graham to the inaugural FIM World Championship but the twin-cylinder racer did not fulfil its initial promise in the following two seasons. Not only was it beaten by its four-cylinder Italian rivals, Gilera and MV Agusta, but also by Geoff Duke on the single-cylinder Manx Norton.
These disappointing results convinced the AJS directors to commission a complete redesign of the engine for 1952. The original motor had a horizontal cylinders layout with heads that featured unique castings with multiple spikes instead of conventional finning. These took maximum advantage of the oncoming airflow and it was their distinctive appearance that led to the motor being nicknamed “the Porcupine”.
For the updated version of the 500cc twin AJS, R&D boss Ike Hatch produced a revamped engine with the cylinders now at 45 degrees from horizontal. As the cylinder heads would not now be facing directly into the oncoming airflow their cooling spikes were discarded in favour of conventional finning that was easier and less-expensive to cast and machine-finish. Even so, old habits die hard and the new ‘spikeless’ engine was still referred to by race fans as “the Porcupine”…
The revised engine retained essentially the same internal layout as the original but with changes to the twin overhead-camshafts, valves, combustion chamber shape and pistons as well as stronger con-rods and crankshaft. The new unit was housed as a semi-stressed member in an open-cradle frame and had a dream debut by finishing 1-2 in the season-opening Swiss Grand Prix with new team member Jack Brett winning the race ahead of Bill Doran, and AJS’s new recruit, New Zealander, Rod Coleman placing fifth.
But it was all downhill from there onwards, with Doran and Brett retiring from the 1952 Senior TT that was won by Norton’s new signing, Reg Armstrong, ahead of MV Agusta-mounted Les Graham – both former AJS works riders! Coleman was fourth in the Island, with Bill Lomas fifth. Rod 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 place in the Ulster GP, the last ever run on the Clady circuit with its punishing seven-mile straight.
The new version of the AJS twin was again demonstrating some potential as Coleman’s teammate Jack Brett had rounded the last turn, less than a mile from the finish, and heading for victory – only to have its drive chain jump the rear sprocket! Forced to push in to finish fourth, Brett saw his almost certain win go to Cromie McCandless, having a one-off ride on a works Gilera four. With Brett’s seventh place the best that the trio of AJS riders could manage in the Italian GP at Monza, the company management opted to withdraw from the final Grand Prix of the season in Barcelona.
Unfortunately 1953 was no better. Much worse, in fact! No AJS rider finished on the rostrum in the entire eight-race GP series and fourth and fifth places in the Senior TT for Coleman and Doran were little consolation for a dismal tenth place in the points table for the New Zealander as the highest-placed team rider.
In an effort to make the 500cc twin competitive again, the pragmatic and effective new development engineer Jack Williams completely revamped the whole bike for the 1954 season. Performance had now topped out, with 54 bhp at the comparatively low revs (for a twin) of 7800 rpm being the most that the engine could be persuaded to deliver reliably.
Therefore the most attention was paid to the cycle parts. These saw a new lower frame and massive 6.5-gallon fuel tank draped over the engine, to reduce the frontal area of rider and machine due to the short-sighted AJS policy of refusing to use the full ‘dustbin’ streamlining then being adopted by their rivals. The monster tank meant that the bike was not very comfortable to ride in a typical 90-minute GP race and it required a completely new weir-system fuel supply, incorporating a car-derived pump.
The retention of the four-speed Burman gearbox, at a time when the competition now had five-speeders, was a further handicap. Rod Coleman was joined for the season by Derek Farrant and another rising star, Scotsman Bob McIntyre, but with Geoff Duke now riding for Gilera, the AJS was still outpaced and now deficient in the handling department. The new 1954 version of Gilera’s fast four-cylinder bikes now handled properly thanks to Duke’s invaluable input after his years on Manx Nortons with their then-icomparable ‘featherbed’ frames. The AJS was also hampered by the company management’s insistence on retaining their own factory’s suspension units instead of the Girling spring and damper combinations that Norton had conclusively proved to be the best .
A pair of fourth places for McIntyre in Belgium and Coleman at Assen were the best GP results all year long although the New Zealander did get the better of the works Gileras just once, by winning the non-championship Swedish GP at Hedemora in what would be the bike’s final race in factory guise. Coleman’s 12th place in the end-of-season table and fifth for AJS in the Manufacturers’ points standings underlined that, spikes or no spikes, the Porcupine’s day was done and it went into hibernation.
It did stir from its slumbers once, though. A decade later, established AJS/Matchless dealer and race tuner Tom Arter obtained a complete bike and parts from the factory, where his rider, Mike Duff from Canada, had noticed it lying forlorn outside the race shop. Arter resurrected the bike and Duff used it to finish seventh in the wet Hutchinson 100 race at Silverstone in 1964. The born-again vintage racer was by then fitted with a dolphin fairing and a conventional fuel tank with gravity feed and Arter next took it to the Isle of Man for Duff to perhaps ride in the Senior TT. There it was clocked at 143 mph in practice (faster than the Matchless G50 that Duff was actually entered on) but any idea of racing it was aborted when cracks were found in the magnesium crankcases. The days of an AJS twin in any meaningful competition were over. Now the bike is in a private collection and rarely seen in action.
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