Author Topic: YZ125K 1983  (Read 14804 times)

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Offline alexbrown64

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Re: YZ125K 1983
« Reply #120 on: November 27, 2015, 11:57:35 PM »
The ring end gap is way too small...imagine when hot. That said your piston has gripped...could be the excess heat from the rings swelling the piston more, or the bore was not opened enough for that piston/ring set.
Chris, i ran a feeler gauge between the cylinder and piston and got between 0.05mm and a tight 0.08mm.  Wossner recommends 0.06mm on their website.  So roughly, the piston gap is correct.  I believe the ring gap is the culprit.
Mboddy, i had another cylinder on this bike and with same oil etc, all was fine.  Today was the first run with a new cylinder and piston. 
Whats the consensus on honing the cylinder, cleaning up the piston, setting the ring gap and slapping it all back together to run in.... or take it to a bike shop to get miked up and they will obviously recommend a new piston etc..

Offline 2fITy.J

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Re: YZ125K 1983
« Reply #121 on: November 28, 2015, 12:06:14 AM »
I agree the ring gap is the culprit. But the marks are on the piston so there is some transfer of heat or something else amiss to do that.

Personally I would rehone the cylinder till I was satisfied the ring end gap was okay after I was well satisfied I had the correct piston and rings for the size you were needing. Get everything measured.


Cheers,
Chris.
A bike in the bush is worth two in the shed!

BMW-BSA-Ducati-Honda-Kawasaki-Lambretta-Matchless-Norton-Suzuki-Triumph-Vespa-Yamaha.

Dirty Dozen '13 DR650SE - '90 DR650RS - '82 IT465J - '82 IT250J - '80 GT80G - '77 A100B - '76 DT100C - '76 TC125 - '75 TM75 - '73 MX80 -       '73 TC100K - '69 TC120-1

Offline alexbrown64

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Re: YZ125K 1983
« Reply #122 on: November 30, 2015, 09:47:21 PM »
Decided to take the cylinder and piston in to get measured and fixed.  I am also buying a micrometer and telescopic bore gauges to check everything myself before i slap it all back together again.
Will update when its all done.
Cheers,
Alex

Offline fred99999au

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Re: YZ125K 1983
« Reply #123 on: November 30, 2015, 10:15:14 PM »
Excellent investment. Good quality measuring tools are not really expensive, but last a long time if looked after.

if used as hammers, then not so much.