When to replace piston?

[MikeG4936]

I had a lean run on my YS 60SR and lost some compression. I purchased a ring, piston, and sleeve, but I am unsure if I should replace the piston or not.

I purchased the new piston because the old one has some minor scoring on it. It is my understanding that only the ring and the liner come in contact - so if those are brand new, should I even bother replacing the piston??

[DaveHolland]

To me it depends on how bad the scoring is on it. If there is scoring on the piston above the ring then I would replace it. If its just tiny marks below the ring then its ok to me. If they are more than just a tiny little scratch then I would replace it. It has a chance to heat up and expand scoring the sleeve again.