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| In 1981 the racing world saw the arrival of a brand new Yamaha 250cc racing machine the TZ250H (5F7). From 1972 until 1980 Yamaha had produced their air / water-cooled racers based on the DS7 Road engines. The new TZ250 productionracer was a complete new machine in all aspects. It featured what Yamaha called the YPVS (Yamaha Power Valve System). In order to be ahead of production Yamaha already produced this machine in 1980 for a selected number of riders to test this machine. The factory code for this model was OW47. From 1980 until 1985 all models built were OW47 machines, although they differed on many points. This period was an apprentice period for many young engineers to acquire their experience in racing and develop new production racers. Cylinders were marked OW47, but also unmarked cylinders, pistonvalve, but also crankcase readvalve engines, cylinderheads marked OW77 (125cc 1984) were used. There is not a lot of centralized data kept of this period. | ||
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