125-200cc Compression: Rings or Rebuild

Hey Guys,

If the compression reading is below 160, do you assume re-build or is re-ringing an option?

And if you are re-building for the first time, is an oversize bore assumed or can you drop in a stock-sized new piston and call it a day?

Thanks!

160 isn't that bad.

You shouldn't have to overbore, unless you have damage to the cylinder wall. Stock piston should work.

Depends on what it is. A CR150 only has about 145-150 psi. 160 is probably very good.

Hmmm...something must be off on my gauge as the bike is a 2012 CR125. Back to the garage!

I was told mine should be 160-165.
At 25 +/- hrs it was 140-145, so I did a ring. After the ring, it was 145-150.
After doing a bunch of searching on here, it seems that my numbers are normal, but the 125 may be a little higher.

Look in the manual for your bike, find the wear limit/maximum piston to cyl clearence. Measure it exactly how the manual tells you to. Doing it this way removes the guess work! It would be safe to assume if you have say 25 hours on it, and have used up .002 worth of clearance. You will use another .002 in 25 hours.Don't skip measuring the squish band clearance eaither. The lower portion of the piston is widest, so you will have to slide the feeler guage in far enough to reach