KAWASAKI H1R
The green genius that challenged Ago when no one else came close
Alone among the four Japanese manufacturers, Kawasaki turned its back away from twostroke GP racing at the end of 1982, in favour of exclusively concentrating its race efforts on the four-strokes it sold for the street. Yet it was the manufacturer of the Green Meanies which was responsible for building what is arguably the most significant motorcycle in the history of the 500GP class – the threecylinder 500cc two-stroke Kawasaki H1R. It was the bike that ushered in the modern era of competition technology when it made its debut on the world stage in 1970. Kawasaki had already stunned the world in 1969 by launching the first large-capacity two-stroke street bike of the modern era – the 500cc H1 Mach III, a true hooligan bike that was the first headbanger’s hotrod. Inevitably, it swiftly ended up on the race tracks of the world, where it gained further street cred by being immediately competitive and surprisingly reliable, as well as numbingly fast by the four-stroke standards of the day. It sprung an upset victory in the 1969 Le Mans 1000km endurance race, and came close to winning the Bol d’or 24-hour marathon, finishing second, third and fourth after yielding the lead to the winning 750 Honda only in the final hours.
For a company whose greatest success on the track until then had been to win the world 125 Grand Prix title with Dave Simmons riding its rotary-valve parallel-twin that same year, it was a short but inevitable step to develop the full-on 500GP production racer that the Mach III had seemed destined to spawn. In doing so, Kawasaki altered the face of Grand Prix racing forever.
Unless your name was Agostini, and you could parade to a series of unchallenged GP victories and world titles on Count Agusta’s MV four-stroke triples, your main option to race in the GP class up until the end of 1969 was a Matchless G50 or Manx Norton that was at least 40mph slower than the MV, but had the benefit of being cheaper to run and easier to maintain than the Italian Paton and Linto twins, which were a privateer’s only other choice.
Nominally overbored 350 strokers were permitted, however. The first time a two-stroke ever finished on the rostrum of a 500GP race was when New Zealander Ginger Molloy took his 360 Bultaco single to third place in the 1969 Spanish GP at Jarama – out of just seven finishers!
But two-strokes weren’t really competitive in 1969. A year later, they were – and Molloy, an experienced member of the Continental Circus who was his own mechanic and knew better than most how to prepare a fickle, seizure-prone two-stroke racer of the era, was the man who proved it. He did so by finishing runner-up to Ago’s MV Agusta in the 1970 500cc World Championship, in the debut season of Kawasaki’s H1R customer racer. Closely based on the H1 Mach III roadster, the 40 air-cooled H1R road racers Kawasaki built for sale 50 years ago employed the same crankcase, cylinder and detachable cylinder head castings as the H1. The 498cc piston-port engine’s architecture featured three separately cast air-cooled cylinders, each with a large single intake and exhaust port and five transfers, mounted transversely in line on the crankcase, and fed by a trio of specially-developed Mikuni VM35SC carbs, which most owners bored out to 36mm.
Lubrication was provided via Kawasaki’s trademark injector system supplied from an oil tank in the seat, and mounted on the right end of the 120° crankshaft. This fed the main bearings, big ends and, via the oilways drilled in the special H1R rods, the needle roller small end bearings, although some owners mistrustful of it dispensed with this system in favour of around 5% premix fuel.
But once those educated on four-stroke singles had mastered the critical skills of setting the carb jetting on a two-stroke correctly, the H1R gained a reputation for reliability – only broken cylinder studs were a perennial problem.
Forged two-ring pistons, 20 grams lighter than the Mach III equivalents, with offset wristpins to reduce slap at either end of the piston stroke, were fitted to the 60mm x 58.8mm engine. The five-speed close-ratio gearbox was matched to a dry clutch mounted behind the oil injectors, while the Mach III’S electronic ignition was replaced by a battery and three separate coils for the racer, complete with alternator – apparently Kawasaki technicians thought the CDI was too complicated for racers to understand. However, most owners like Molloy fitted a Kröber transistorised system, which saved lots of weight by letting them junk the battery, alternator, etc, as well as preventing misfires caused by any slight movement in the crank bearings upsetting the points timing. Delivering a claimed 75bhp at 9000rpm in stock form – over one third more than a Manx Norton or Seeley G50, which actually weighed more dry than the 135kg Kawasaki – the H1R’S biggest handicap was its fuel consumption, around 16mpg. But scare stories about 11mpg thirst which arose when the bike made its debut at Daytona in March 1970, only came about through confusing Imperial and American gallons!
Even so, the fuel load needed to satisfy this thirst, in the days when FIM rules stipulated GP races must be at least one hour in length, was a real penalty. This was true not only in terms of weight and lost time making pitstops to refuel (as all H1R riders who didn’t use premix had to do as a matter of course in GP races, even once the oil tank in the seat had been converted to a secondary fuel tank, and a new oil container was mounted above the gearbox where the battery used to be), but also because a bike already featuring some compromises in its chassis design didn’t
‘THE 498CC H1R ENGINE GAINED A REPUTATION FOR RELIABILITY’