YZ 125 top end rebuild - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 01-31-2002, 01:50 PM
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YZ 125 top end rebuild

I'm looking at buying an '86 YZ 125 real cheap. It runs fine right now, but his buddy told him it will probably need
a piston and rings soon. My question is if the rings are worn, why would it need a piston too? And, if it needs a piston, wouldn't it need to be bored (if not oversize already)? Last, how difficult is it to rebuild the top end, I'm an automechanic, but haven't worked on bikes for about 16 years! Thanks for any advice.

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post #2 of (permalink) Old 02-01-2002, 03:30 PM
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Re: YZ 125 top end rebuild

it takes about a hour to do a top end on a 125. you should replace the piston on a 125 sinc there is only one ring. on my 250 99 yz i will do a piston and rings and the next rebuild i will do just rings. but i rebuild my motor every 25-35 hours. hoe often you gonna rebuild that 125? plus its like 100 for everything for a top end. you can stick with the stock size if the cylinder has been plated with nicosel or something of the sort. this is a very hard surface that wears cery little over time. if its a standard cylinder then bore it .20 over just to be on the safe side and get a nice hone job. 125's run at really high r's so the piston gets a lot of abuse

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