The AJS Porcupine—First Grand Prix World Champion | One-Year Wonder

As the winner of the very first FIM 500cc World Championship in 1949, the AJS E90’s position in posterity is assured. What’s surprising is that the “Porcupine”—nicknamed for its signature spiked cylinder fins—remains, 63 years later, the only twin-cylinder bike to ever win the premier-class title. Singles won it, as well as triples, fours and even V5s in the modern era, but never another twin. The Porcupine was both the first and the last.

AJS was a division of Charles and Henry Collier’s Associated Motor Cycles (AMC), a firm that at one time or another also included James, Matchless, Norton, Sunbeam and other, lesser-known British brands. The Porcupine’s 500cc parallel-twin originated during the final days of World War II as the supercharged, liquid-cooled Sunbeam E90S—a prototype design binned after the FIM banned supercharging in ’46. Engineer Vic Webb, with help from legendary Vincent designer Phil Irving, hastily fashioned the remains into a naturally aspirated motor for a new AJS Grand Prix bike. The unique E90 layout—with aluminum cylinders angled just 10 degrees above horizontal to leave room for a blower above—was retained, but it was converted to air-cooling.

The E90 was quite advanced for its day, with almost “square” 54.0 x 54.5mm cylinder dimensions and unit construction with a geared primary drive. Individual intake and exhaust heads hold hollow cams driven by eight gears running up the engine’s right side in a Y-shaped case. A 360-degree crank brings both pistons up and down in unison, and rotates backwards—another vestige of the supercharged design. There is no flywheel, either, as supercharger drag would have made the flywheel effect redundant. Unfortunately, the resultant abrupt crankshaft action frequently splintered the E90’s magneto drive.

With the laydown engine mounted in a low-slung, double-cradle frame, the Porcupine handled inherently well. Unfortunately, AMC chairman Donald Heather obstinately refused to allow anything other than the firm’s own woefully ineffective Teledraulic fork and abysmal Jampot shocks to be used, which was a major setback against the Girling-suspended Nortons.

The odd-looking Porcupine didn’t set the world on fire when it debuted in ’47—Les Graham’s ninth-place finish at the Isle of Man was the team’s best result that year. Major development continued in ’48, however, culminating in a works Porcupine setting a total of 18 speed records at Montlhèry, France—a good confidence-boost in preparation for the first-ever official roadracing world championship the following year.

The AMC/AJS works team dominated this inaugural six-race series, with Graham winning the rider’s title and AJS taking the manufacturer’s crown. The season started on the wrong foot: Graham led the Isle of Man Senior TT for almost the entire race before a broken magneto drive at Hilberry left him pushing the bike across the line to finish 10th. He recovered to take victory in Switzerland on Berne’s grueling Bremgarten circuit—the Porcupine’s first GP win—and won again at Ulster, Ireland. Graham then finished second to Nello Pagani’s Gilera Four at Assen, Holland, and was forced to retire with a split fuel tank at Spa, Belgium—a race won by teammate Bill Doran. Only a rider’s three best results counted that year, however, so even before the season-ending Italian GP at Monza, Graham had done enough to claim the world championship.

Detail improvements made for ’50—including a larger fuel tank and streamlined seat—utterly failed to address the Achilles heel of ignition and carburetion/fuel-starvation problems, resulting in far too many DNFs. Add to that stiffer competition from an all-new, better-handling Featherbed Norton and even faster Gilera Fours, and AJS was knocked down to second best. Graham repeated his Swiss victory, and finished second to Geoff Duke’s Norton at Ulster, but it was only good enough for third in the series.

AJS never factored into the world championship again. In ’52 an all-new E95 parallel-twin debuted, its cylinders almost conventionally located 45 degrees above horizontal. AJS riders finished 1-2 in the season-opening Swiss GP, but it was downhill from there. Results were even more dismal in ’53, without a single rostrum finish in eight races. It was more of the same in ’54, at which point the AMC board officially pulled out of GP racing. Only privateers waved the AMC flag after that, riding Matchless G45 pushrod twins and G50 singles.

The parallel-twin Porcupine’s moment came and went quickly. But for a single year—1949—slightly greater power output compared to a single, coupled with slightly better handling compared to an inline-four, proved the best of both worlds. The best in the world, as a matter of fact.

The stillborn Sunbeam E90S prototype, stripped of its supercharger and converted from liquid to air-cooling.
Gilera Quattro 500/4, Norton Manx, Moto Guzzi Dondolino
Tech Spec

Price na
Engine type a-c parallel-twin
Valve train DOHC, 4v
Displacement 498cc
Bore x stroke 54.0 x 54.5mm
Compression 9.0:1
Fuel system Single Amal GP carburetor
Transmission 4-speed
Claimed horsepower 48 bhp @ 7600 rpm
Claimed torque na
Frame Tubular-steel double-cradle
Front suspension AMC Teledraulic fork
Rear suspension Twin AMC Jampot shocks
Front brake Twin-leading-shoe drum
Rear brake Single-leading-shoe drum
Front tire 21.0 x 3.00 Avon Speedmaster
Rear tire 19.0 x 3.25 Avon Roadrunner
Rake/trail na
Seat height 28.0 in.
Wheelbase 56.5 in.
Fuel capacity 6.5 gal.
Claimed curb weight 374 lbs.
Color Silver
Verdict 4 out of 5 stars.

For one moment in time, this twin offered exactly the right combination of horsepower and handling.

British collector Sammy Miller bought this E90 Porcupine from ex-AJS works racer Jock West in the late 1970s. It’s believed to be the only example left in the world.
The almost-horizontal cylinder layout was intended to make room for a supercharger above the engine. Deep cooling fins inspired the
A large underseat oil tank and bulbous, 6.5-gallon fuel tank make the Porcupine look more porcine than it is. Just 374 lbs. wet, it’s actually quite compact.