366 motor...Why can't I find parts?

[v8-914]

I bought a used salvage motor. I am rebuilding it now, but parts are becoming an issue. It appears that Big Bore kits are non-existent for the 366 as are 2nd oversize pistons. Mine are 75.25 mm and ring gap is .027. My new, used engine is S650 212123 and it shows to be a 73 TX-650. What's the deal?

 

[650Skull]

Any 256 part will do. Basically the same, Yamaha changed the model code of the bike. That is why on parts lists some 256 part no"s are still used on models into the late 70"s.

The big change in 72, (306), and 73, (366), is the crank is designed for electric start. Same pistons from 70 to 73. Conrods are the same length but did have a mid year change in 70

ID chart shows the code change.

There is some information on the difference in conrod and piston differences.
256, common reference for all engines from 70-73.
447 for all engines from 74-83/4 and
553 for all Euro standard model engines from 75-82

https://www.xs650.com/threads/xs650...workshop-manuals-and-other-information.30569/