Description
26 Page – PDF Download – Complete Series – Yamaha XS750 Engine Rebuild
“Yamaha XS750 Engine Rebuild
Stuart Wright of ‘Big Four’ Motorcycle Engineering will be stripping and rebuilding the 750 Yamaha triple over the next few months, but first, we outline the model’s history and pinpoint the early problems in had.
Some Relevant Information
Yamaha introduced their first motorcycle in 1955 but it wasn’t until 1970 that the world saw their first four-stroke, the 650cc XS1 twin which we first saw as the XS2 in 1972. This model remained in production throughout the 1970s but was replaced as the flagship of the range in 1977 when Yamaha launched the twin-cam three-cylinder XS750 with shaft drive.
The triple represented a big step for Yamaha, who made it clear they were interested in the long-distance touring rider traditionally catered for by BMW.
The BSA and Triumph 750 triples of the 1960s relied on pushrods whereas this first four-stroke triple from Japan went straight to double overhead camshafts in a light alloy head fed by triple constant vacuum Mikuni carburettors with 34mm venturis.
Yamaha designed in smooth throttle response and reasonable torque for pleasant touring, though of course, the engine was more of a revver than its punchier British counterpart, maximum power being 65bhp at 7500rpm.
The crankshaft featured no less than five plain bearings. Big ends were also plain. Primary drive was by four-row Hy-Vo chain rather than helical gear. All engine, gear and clutch components were oil pressure fed by a powerful 5.5kg-csm2 trochoid pump. A replaceable oilfilter was fitted.
A impressive looking engine unit of commendable slimness in its day, the wet sump motor was fired by triple contact break breakers, 12 volt battery and coil. Electric start was standard and the kickstart lever was retained for emergencies.
The five speed gearbox did not afford the slickest of changes, but it was fairly positive and felt robust. It was after all a shaft-drive touring rather than a sports machine…”
26 Page – PDF Download – Complete Series – Yamaha XS750 Engine Rebuild
