piston wear

[budpat105]

To the experts: doing my first rebuild on my Combat wombat. I have no history on motor, I did start it but never rode it due to gas tank issues. I am going to rebuild motor, pulled top end, stock bore and no scuffing on piston or cylinder! I turned cylinder over and put piston in it. I can get a .007 feeler gauge in by the piston skirt, cannot get a .008 in. Do pistons wear? Do I need an overbore? Do I want .003 clearance? Thanks

[Bullfrog]

The Official Hodaka Workshop Manual lists maximum allowable clearance for the 125cc engines at 0.008" - so you are 7/8ths of the way there. Seems like it is definitely time to do something . . . most likely a bore a job.

Yes, pistons do wear - but the cylinder bore was wearing right along with the piston. So the bore is probably slightly out-of-round AND probably worn more in the area near the intake port than up near the top of the bore ("taper"). A precision measuring job on the bore would be in order to establish the amount of wear . . . but the odds are heavily on the side of enough wear that a bore job is needed.

I'm partial to 0.002" clearance on a new bore job . . . with a proper break-in involving several cycles of bring the engine up to full operating temperature then letting it cool down completely to ambient temperature before running it again.

Ed