Compression, CR 125

[00CR125]

Does anyone know what the compression is supposed to be on a 2000 cr 125? I checked mine and its running 155lbs. Im not quite sure the gauge i used is totally accurate though. Any help would be appreciated.

 

[marcusgunby]

If it has a std piston ring that comes gapped at 18thous it will show around 150psi even when new.If it has a different piston/ring it maybe higher.I never use the comp reading as a test as ive seen a KTM engine go bang in a big way that had a really good comp reading 10 minutes before, the comp reading tells you nothing about piston condition.

 

[00CR125]

How can i check the piston without compression test? Usually if comp is good, piston and ring are good, atleast thats what i do with cars, and i work at an auto shop..

 

[motometal]

do not confuse failure due to material fatugue, and wear/sealing of the engine parts.

I would say the piston should be replaced after a reasonable number of hours. Opinions vary, I would say on the average once per season at least on a 125, and thats assuming it isn't run too hard. High rpms and more hours per week could dictate a top end every few months...just depends how much you ride. It is possible for an engine with many, many hours on it it still show good compression, even though the piston is loose enough and/or fatigued enough that it could go at any time.

 

[marcusgunby]

I always use no of hours-expert use 12 hours , novice use 25hours.If its a second hand bike i always would fit a new piston to be sure.

 

[helio]

00CR125,

I have 95 hours with a vertex in my CR 125 in woods. I can read 150 psi and the bike starts after 1 or 2 kicks...for me is like new. But I decided to replace this piston to be safe.
Now I can sleep in peace :aj: .