97 rm125 low compression on new top end

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4/1/2018 10:40 PM

I helped a friend rebuild his 1997 rm125 it took like 10 kicks to start up the first time. He took it out for a ride today and ran fine for 2minutes then started sputtering. Now the bike wont start and ge said it has low compression. Any causes and how do I fix this? Thank you!


4/2/2018 1:12 AM

Try again on the rebuild. This time double check piston to cylinder cleaeance and ring gap.


4/2/2018 7:17 AM

Piston ring stuck? Installing without lube or with debris in the engine will cause that.


4/2/2018 2:19 PM

Also if the ring end gap was to tight will cause the ring to stick.
An air leak will cause a lean condition that will cause it to over heat and stick the ring. A bad crank seal caused by a bad crank main bearing will do the same.
A rod bearing can cause the same thing as the excess heat will travel to the piston.

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