74 Z50 Motor Rebuild

zfleming

New Member
1974 Z50
Rebuilding the motor on my 74 z50 only because there was metal in the oil due to a chipped casting.
With that, should I flex hone the cylinder if using exiting rings. What flex hone?
It had great compression and no smoke.
 

OLD CT

Well-Known Member
If you are going thru the trouble of honing it, if you can find a hone small enough, new rings would be a MUST.
If you are ''cheaping out'' using old rings why bother, it's not going to make a difference. Either you get lucky or you don't.
 

zfleming

New Member
gotcha, it was one of things I learned with my grandpa. If your gonna hone, go all new. But if not, leave it be.
Just trying to figure out if it make sense.
 

OLD CT

Well-Known Member
Try to find a 40-42mm hone and go for the new rings. Might as well do it right.
Don't forget to use 4 stroke M/C oil only. No car oil. Ebay item# 283250539109 is a hone I found.
If you could get a machine shop to hone it for 10 bucks, it would be worth it. For $30 you get to keep one in the tool box for next time.
 
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69ST

Well-Known Member
If this was a 72cc motor, I'd say measure the bore first. But, the tiny bore size of the 49cc version of our fave engine has an advantage...the piston skirt, proportionally, is very long. For that reason, we see a lot of 39mm cylinders that are still within spec. You don't want to actually hone the cylinder, technically speaking that means taking it out precisely to a finished size. All you want to do is de-glaze it...give it a light cross-hatching, to seat the new rings. That's a very quick process, few seconds with a drill & dingleberry hone. As long as you see a uniform surface finish, top-to-bottom, you're good to go. OTOH, if you see score marks, the rings will never seal and it'd be time for an overbore. And, that's the most common reason for taking a z50 cylinder oversize...unlike the bigger (47mm & up) versions which are more likely to be worn beyond spec.
 
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