The beasts under the 750 machines were without doubt Yamaha’s 700/750 machines. The factory machines differed from the TZ machines. In 1976 Yamaha started with the OW31, which was updated each year. Different frame, different frontfork, aluminum swingarm, different cylinder and heads, carburetors, ignition, exhaust pipes etc.
The YCRT OW31 has the actual crankcases used by Steve Baker in 1977. OW31-E-808