z50r question

[skip1701]

Hi all, it's been a while since my last question and I havent forsaken my elites. I'm have been tasked by my employer to rebuild his 1982 z50r.. I know you guys are gonna say "but it's a 4 stroke!" .Well it only had 30psi of compression and the rings look great. The piston is scored but this is strange: the bore is polished fairly smooth. What gives? I would have thought that a scored piston would result in an equally damaged bore. My plan is to replace the piston, rings and hone the bore. Should I replace the piston or just clean it up and go with the hone and rings? Any advice folks would be great!

[Bear45-70]

I see marks in the bore. Can you catch a fingernail in them, it so you need to bore the jug.

[skip1701]

I ran my nail across all the visible scratches..i tried to catch them but could not..does this mean all i need is a good hone job? and what about that pesky piston? stock size or a little bigger..rings are a no brainer.

[Bear45-70]

Yes

[eliteguy50]

I ran my nail across all the visible scratches..i tried to catch them but could not..does this mean all i need is a good hone job? and what about that pesky piston? stock size or a little bigger..rings are a no brainer.

Usually yes. You can't go bigger on the piston if all you are going to do is hone the jug.

[tru72]

isnt a zr50 motor like a crf 50 motor?
you might check the valves, That score doenst look that bad...

[wiguy05]

I have an 88cc big bore top end for sale if you are interested.

[skip1701]

I cleaned the head and tried something strange..I manually opened and closed each valve then set the head up so i could pour alchol into the intake runner and let it sit....30 min later no sign of leakage...did the same to exhaust..i know it sounds weird but i did it..and can i polish the scores on the piston or replace with a new one?

[Bear45-70]

You can not polish the piston.