Who here has rebuilt a motor with a holed piston?

[jfman]

Id be on the hunt for a spare GS400. They can be found are here (sitting bikes with good motors) for cheap.

I already got two spare GS400 motors.

[MWGS400]

Well, its been a while but I haven't forgotten about her. Found a 1982 gs400 motor and I'm wondering if I could swap the '82 top end onto my '78. Anyone have any idea? I'd do the whole motor but I want to keep my kickstart.

[tkent02]

I think I'd lose the kickstart and keep the later engine intact. Espacially if you are pretty sure it works well. Putting the parts on your engine that has already failed once is opening a big bag of worms for sure. I don't think they fit anyway.
Kickstarters lose all of their appeal after a few thousand starts.

[Mekanix]

Well, its been a while but I haven't forgotten about her. Found a 1982 gs400 motor and I'm wondering if I could swap the '82 top end onto my '78. Anyone have any idea? I'd do the whole motor but I want to keep my kickstart.

No, sorry. The cases do not match up. Bore and stroke are not compatible and oiling is not the same for the top end.

The 400 engine case will not directly fit in your frame without modifications.

Best to rebuild yours or bore it bigger if you want to keep that motor.

Your cutoff date is early 1979. After that they are a different engine altogether.