Topic: Piston help...

[torchmonkey]

...for a '75 CB750f. Bought a bike w/ a stuck motor, 2 pistons are usable, they are marked "392." Bought a parts bike (same year, model, etc) and would like to salvage 2 of the 3 usable pistons from it, they are marked "300." Are these interchangeable?

[Old Scrambler]

They are interchangable but not necessarilly to be mixed in the same motor. Piston weight may vary....the rings may be different.......?  If the motors were stuck, you may have issues with cylinder clearances or uniform roundness. Be sure that your valves are moving freely in the head. One or more are usually stuck. 

[torchmonkey]

Thanks, I already had the valves lapped and head rebuilt as well as having the cylinders honed. Just trying to avoid dropping $600+ on a set of Wiseco. I'll have a look at the fourth piston, looked like the rings were stuck to it.
As far as rings go, the oil ring is totally different, one piece as opposed to three.