Yamaha XS650
FIFTY YEARS AGO in May 1968, Yamaha rolled out the prototype of their first four-stroke road motorcycle – a machine deemed so controversial that at first they decided not to sell it in the UK.
The XS1 had a parallel twin engine and would have been be in direct competition with British machines. Yamaha importers in the UK felt this would upset British buyers too much. The big Yamaha twin’s design has origins that stretch way back before the late 1960s. It starts with Horex, a German company that in 1954 built a 400cc, and the later 500cc SOHC parallel twin that was years ahead of its time.
A Japanese company, Hosk, took the Horex, reverse-engineered it so that the engine had a separate gearbox and produced a 500cc twin that rivalled British equivalents for top speed. Later they took it out to 650cc. Hosk went out of business and were taken over by another manufacturer, Showa, who were, in turn, taken over by Yamaha in 1960 who, at the time, were far more interested in building fast two-strokes than four-stroke twins.
That was until 1967, when Yamaha were helping Toyota develop the engine for their 2000GT sports car, a DOHC straight six. With the knowledge gained from building the Toyota and the long-forgotten bones of the Hosk gathering dust, Yamaha came up with the engine for the
