AJS V4 500
The AJS V4 went from air-cooled, unblown show bike to water-cooled, supercharged race-winner, with the first 100mph lap on a UK road course
In a country so long wedded to single-cylinder supremacy, where describing a motorcycle as a ‘multi’ for many decades denoted nothing more exceptional than a parallel twin, the idea of a four-cylinder 500cc GP racer ‘Made in England’ always seemed at best unlikely.
But, just once, back in the 1930s, a British manufacturer dared to invest in the exotic rather than the functional. The result took a while to win a race, due to a desultory development path that was first interrupted by World War II, then terminated by the post-war ban on forced induction, but it led in due course to the creation of the bike which won the first ever 500cc World Championship, in 1949.
That manufacturer was Associated Motorcycles (AMC), the parent company for AJS and Matchless. The AJS marque would go on to produce the famous E90 Porcupine, which, with that championship victory in 1949, became the only twin-cylinder motorcycle ever to win the 500cc world title – an achievement unrivalled to this day. But its pre-war predecessor from the same company, the supercharged AJS V4, had also earned its place in the record books by becoming the first bike to lap a classic road course at over 100mph.
That was in the hands of Walter Rusk at the 1939 Ulster Grand Prix, which was run 15 days before the outbreak of World War II. The post-war parallel-twin ‘Porc’ was, if not exactly a conventional piece of kit, certainly a much less exotic one than its pre-war predecessor. The fact that the only surviving examples of each bike have been brought together by Sammy Miller, who regularly puts them through their paces in public as well as displaying them in his eponymous museum, is very fortunate.
The first and only supercharged GP500 racer produced by a British manufacturer ever to start a race, traces its origins back to an unlikely forebear. In 1931, the Stevens brothers’ Wolverhampton-based AJS factory had closed its doors, another victim of the Depression despite the marque’s glorious record of competition success the previous year. But late the same year, the remains of AJS were acquired by the Collier family’s London-based Matchless firm to create Associated Motorcycles/amc, with the Matchless marque aimed at the more everyday customer, while AJS was pitched as the sporting brand in the group.
When the 500cc V4 AJS road bike was launched at London’s Olympia Show in 1935, it was by far the most exotic and complex motorcycle yet produced by a British manufacturer. Designed by Bert Collier, the air-cooled 495cc 50° V4 motor, with chain-driven single overhead camshafts, was effectively a pair of V-twin engines mounted side-by-side on a common crankcase. Its four individual cast-iron cylinders were topped by separate heads, each carrying exposed hairpin valve springs, with the exhausts for each bank running in opposite directions, fore and aft.
A single Amal carburettor fed the two cylinders on each side, although the makers specifically proclaimed the possibility that the chain-driven dynamo lying low down in front of the engine could be replaced by a supercharger ‘for competition use by those customers of a sporting disposition’.
Sadly, the 1935 show bike was the only V4 AJS ever to be fitted with lights, a pillion seat, licence plates and silencers – because the AMC factory aborted plans to put it into production (leaving Honda to revive the idea 45 years later...)
Instead, AJS adopted the design as its entry into 500cc Grand Prix racing, at a time when Continental manufacturers like BMW and Gilera were exploring the exciting possibilities presented by supercharging. So, while other British rivals such as Norton were still persevering with successful but technically unadventurous normally-aspirated singles for racing, AJS were in on the ground floor of what was seen as the new wave of technological sophistication.
When the AJS V4 first appeared in public during testing at Brooklands in the spring of 1936, it was indeed fitted with a smaller version of the ERA voiturette racing car’s volumetric Zoller compressor, chain-driven at half engine speed to compress the charge from a single Amal TT carburettor into the redesigned aluminium cylinder heads. The rear pair of these had been reversed, so that all four exhausts could run forwards, thus allowing the forced charge from the supercharger to be inducted via a branched housing into the rear-facing inlet ports at a pressure of 8psi. Mounted in the same TT frame used by the firm’s 500 ohc single, slightly modified to house the bulkier engine, the racing version of the still air-cooled V4 motor delivered
51.5bhp at 6000rpm, and also now featured alloy cylinders. The four-speed Burman gearbox employed a dry clutch rather than the roadster’s oil-bath transmission, but primary drive was still by chain, with the drive for the supercharger housed in a forward extension of the same casing.
The bike made its competition debut in the 1936 Senior TT in the hands of Harold Daniell and George Rowley
– but although they impressed onlookers with their speed in a straight line past the Highlander and down from Creg ny Baa, both bikes were lacking in acceleration – a key factor then (as now) for success on the Isle of Man.
Both bikes retired with mechanical failures, and the design evidently needed further development to be competitive against the dominant singles. This meant the V4 didn’t appear again until two years later, by which time the rigid frame had been modified to adopt plunger rear springing, and the bike had acquired better brakes, higher compression and revised, less bulky, induction plumbing from the supercharger. The whole installation seemed more compact, and the AMC race shop had evidently been hard at work refining the design, moving the engine back in the frame to improve cooling to the rear bank of cylinders, as well as to lighten the steering – though to no avail. Bob Foster retired the sole AJS V4 to be entered in the 1938 Senior TT on the second lap, suffering engine trouble caused by overheating – at that particular point, the whole V4 project seemed destined to join the spacious refuse bin marked ‘Great British World Beaters’. AMC did not give up, though – the company commissioned Matt Wright to completely redesign the motorcycle. He had joined the firm from New Imperial in 1937, after producing a series of Tt-winning and world record-breaking motorcycles for the much smaller (but by now defunct) British company, including the first 250cc machine to be officially timed at over 100mph.
To address the V4’s overheating problems, Wright took the logical step of water-cooling, initially by thermosiphon, then later by an impeller mounted on the left end of the crankshaft. While retaining the 50mm x 63mm long-stroke layout of the air-cooled bike, and its 50° angle between the banks of linered aluminium cylinders now cast in pairs and devoid of finning, Wright reversed these so all four exhaust ports were rear-facing, giving a clean run for the straight pipes. The paired two-valve heads now had enclosed valve springs, but still featured a single overhead camshaft per cylinder, driven up the centre of the motor by a long chain running directly off the crank at half engine speed. This first drove the rear camshaft drive pinion, then ran down to a jockey wheel idler mounted on the crankcase face, up over the front camshaft drive, then back to the crank. A spring-loaded Weller blade tensioner mounted at the front took up the considerable potential slack in such a long run, while tongued couplings on each upper drive sprocket drove the four separate camshafts whose ends slotted
MATT WRIGHT
‘THE BLOWER LEFT MUCH TO BE DESIRED,BUT GAVE VERY LITTLE TROUBLE ONCE ONE UNDERSTOOD ITS WHIMS’
into them, with threaded tappets operating the valves.
The hollow steel 180° crankshaft was supported by four rollers and one ball bearing, with two pairs of knife-and-fork steel conrods sharing a common crankpin, to avoid having to offset the cylinders. Ignition was supplied by a pair of BTH twin-spark magnetos mounted low down on the right, driven off the crank by a cluster of bevel gears in the right half of the vertically-split dry-sump crankcases, whose vertical drive shaft also drove the twin main oil pumps.
As previously, the Zoller compressor was mounted low down behind the front wheel, and was chain-driven on the left off the primary drive engine sprocket. The supercharger now delivered 6psi of boost, while instead of the positive oil feed to it featured on the early air-cooled motor, the AJS team now mixed two per cent of oil to the fuel, two-stroke style. “Although the blower left much to be desired, it gave very little trouble once one understood its whims,” noted Wright later. In this form, the engine later used by Walter Rusk in the 1939 Ulster GP was dyno-tested that year to deliver 55bhp at 7200rpm, running 16.5psi of boost pressure and 7.9:1 compression, with a 11/16in Amal TT carburettor facing out to the left immediately under the exhaust port of the left front cylinder, and linked to a massive car-type remote float chamber.
Combined with the same Burman four-speed gearbox and dry clutch, the redesigned engine was installed in a new duplex tubular steel frame, which now had the boxes for the plunger springs incorporated. The eight-inch twinleading-shoe front brake was housed in a wide, deeply-finned light-alloy hub, in an effort to lighten a machine which Wright admitted was “definitely on the heavy side, making it a bit of a handful to ride”.
At 405lb (183kg) dry, the four-cylinder AJS was indeed pretty porky compared to an easier-handling single weighing 40% less – a handicap worsened by the inevitable thirst of a supercharged engine, which meant the fuel load was increased to six gallons via a handsome silver-liveried fuel tank, with a matching oil tank low down in front of the right-side plunger box. Webb-type girder forks dealt with front suspension, with a 21in front wheel and 19in rear.
After initial tests, again at Brooklands where it was fitted with four distinctive fishtail silencing cans to meet local requirements, the AJS V4 made its debut in water-cooled form in Bob Foster’s hands at the North West 200 in May 1939, but, as Wright noted: “a carburettor float chamber which decided to start flooding on the starting line, put paid to our efforts,” .
Two machines were entered for the Senior TT three weeks later, though the race was a disappointment, with Ulster rider Walter Rusk and Foster finishing 11th and 13th respectively in a seven-lap race dominated by the BMW Kompressor twins of Meier and West, representing supercharging done right. But though the team had been troubled with blown head gaskets in TT practice, and with erratic handling which apparently caused strong men to flinch at the sight of Walter Rusk descending Bray Hill on the blown British bike, at least it had finally finished a race:
“Although speeds did not reach our expectations, the machines proved so reliable and provided us with so much data, that by the time we arrived in Ulster for the Grand Prix, we felt fairly cheerful,” said Wright, “especially as we had every confidence in the riding abilities of Walter Rusk and Bob Foster.” Well earned, so it seemed, after hearing Jock West’s account of trying to pass Foster’s earlier-starting V4 AJS in the Senior TT. “I caught him up at the 33rd [milestone], but couldn’t find a way to get past till the Grandstand,” he recalled later. “The AJS was bucking and weaving all over the road, and though my BMW was much better behaved and easier to ride, there wasn’t any space to pass him safely. It looked as if he had his hands full!”
Nevertheless, in what would prove to be the final classic GP race run before the outbreak of war less than a month later, Wright’s confidence seemed likely to be repaid as the two AJS riders led the Ulster Grand Prix from the fall of the flag, ahead of a field including the works Norton team, and Dorino Serafini’s supercharged works Gilera four.
But halfway round the long, fast Clady circuit’s 20.5-mile first lap, with the AJS timed at 135mph along its legendary Seven Mile Straight, Foster retired from the lead with plug trouble. This left his brawny, blond Irish team-mate to wrestle a bike which had by now acquired a reputation as a wayward handler, into a 19s lead at the end of lap three, which he covered at a remarkable speed of 100.01mph. This was the first time that any road race circuit (as opposed to Brooklandsstyle speed bowl) had ever been lapped at three-figure speeds, at least in the British Isles.
Rusk’s supremacy was short-lived, however. Halfway round the fourth lap, a link on the girder forks of the fast, heavy AJS broke – perhaps, as some speculated after seeing him in practice broadsiding through the starting area over the ‘ton’, thanks to the muscular effort in taming a bike that by now had even its creator worried.
“Having seen the erratic way the models navigated over the fast stretches, I secretly wondered whether or not the road would be wide enough for the two to stay together without one or the other becoming a casualty,” wrote Wright later, on the impression given when his two riders dashed off together at the start.
In the event, Serafini’s Gilera won the final race before the outbreak of war 15 days later, a conflict which Walter Rusk was sadly not to survive. Having volunteered for the RAF at the outbreak of war, and characteristically set a training school record by flying solo after just 4½ hours of tuition, he died when he crashed his Hawker Hart trainer in Leicestershire on October 8, 1940. Rusk’s historic ton-up lap of the Clady circuit aboard the AJS V4, in recognition of which he was awarded the MCUI Gold Medal, proved to be his last-ever lap on a racing motorcycle.
With the resumption of racing after the war, it was in June 1946 at the Chimay circuit in Belgium that the AJS V4 finally scored its only victory in the seven races it competed in during an eleven-year competition career interrupted by war. In the hands, somewhat ironically, of Jock West, AMC’S new sales manager – who at least had had a foretaste of what to expect, after following Foster around in the Senior TT seven years earlier – the supercharged British bike took the chequered flag first in Chimay’s GP des Frontières, at an average speed of 127 kilometres per hour (78.9mph).
But a second outing a month later at Albi in France resulted in retirement on the penultimate lap, when the engine seized a crankpin and locked solid, with West well in the lead and headed for a repeat victory after setting a new lap record at 140kmh (86.9mph).
By now the AMC board had decided to invest all their available resources in developing the new Porcupine twin, with the aim of gaining Grand Prix supremacy – an endeavour which ultimately resulted in that inaugural 500cc World Championship title for Les Graham in 1949. That same year, the FIM banned all forms of forced induction for road racing, ending the era of the fearsome supercharged GP bikes.
WALTER RUSK STRONG MEN FLINCHED AT THE SIGHT OF WALTER RUSK DESCENDING BRAY HILL ON THE BLOWN BIKE