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We are all familiar with the successes of the
Yamaha M1, an inline four-cylinder honored with glory, but few remember another inline four-cylinder, the 500 2-stroke OW35K with which Kenny Roberts won three consecutive 500 world championships from 1978 to 1989.
Is this enough, however, to say that Yamaha is a manufacturer of inline-four engines? Absolutely not for those who know the history.
In 1981, in fact, the Iwata company abandoned the in-line configuration to race with the OW54, with a square four-cylinder engine with rotary-disc timing. A similar architecture to that of the Suzuki RG 500 that later won the title in 1981 to 1982 with Marco Lucchinelli and Franco Uncini.
The 'square' engine, however, soon showed its limitations and was replaced in 1982 by a new 4-cylinder V-shaped engine. Beginning with the 1982 Austrian GP Kenny Roberts had available a new motorcycle: the 0W61, powered by a V-shaped 4-cylinder with a 60° angle between the cylinder banks, two crankshafts rotating in the same direction, and rotating disc power supply.
It was followed, in 1983, by the 0W70, equipped with a "Deltabox" aluminium frame and 17-inch front wheel, with which the American fought throughout the season with Freddie Spencer's Honda NS 500, finishing defeated only in the last race. Further evolution was the reed-powered 0W76 (1984) (140 hp power), taken to the world title by Eddie Lawson.
More radical changes occurred with the 0W81 of 1985-1986, in which the crankshafts became counter-rotating, reducing the gyroscopic effect of the engine and gaining 5 more hp than the 0W76. An evolution of the 0W81 was, in 1987, the 0W86, with revised expansions to fit within the sporting regulations.
Further changes were made in the '88 season, a year in which the engine was revised (it was mounted more angled downward), which saw the angle between the cylinder banks widen to 70°, so as to allow the installation of a larger reed valve stack. Also new was the swingarm, of the "banana" type , so shaped to leave room for expansions. With this bike, christened 0W98, Lawson won his third world championship title, winning 7 out of 15 GPs.
The new Yamaha four-stroke V-engine could debut as early as 2025, should it prove sufficiently competitive. There is currently no firm word on the debut, which could be at Sepang with Cal Crutchlow, but possibly also Andrea Dovizioso, at the helm.
