Low Compression?

[dirtsurfer31]

I already posted something in a different forum by accident and was moved to gerneral maitanence. This should be the correct place for it. Anyways...

I have a 2000 Honda CR125 and last season i replaced the top end mid to the end of the season. The piston seemed to be in specs but there was a lot of blow-by on the piston. I replaced the piston, ring, small end bearing, and the wrist pin. I replaced everything with stock honda parts. Before this work my compression what at about 145psi with a cold motor. Now, after the break in, it is sitting at about 135 psi, whats going on? I have new boyeson power reeds that are sealing properly (although i forgot to replace the gasket?) And i also took the glaze off the cylinder with a 600 grit wet emery cloth like my clymer manual says.

Does anybody have any suggestions on what i could do to get back my lost compression?

Thanks (i can post pics of old parts if you want)

 

[agitt73]

piston should have been replaced also could very well be the problem also could be the cylinder could be wore bigger

 

[dirtsurfer31]

The piston was replaced. It was replaced with a new, stock honda piston. The cylinder should be fine because i had more compression before replacing the top end with a new one.

 

[agitt73]

another thing could be your ring never sealed

 

[dirtsurfer31]

You mean seated during break in? I broke it in as follows:

i break it in easy. Let it idle for a bit in my garage (up to operating temperature. Let it cool down. Then took it out to the track. I drove it for 15 minutes each time and let it cool until the cylinder and radiators were cool to the teach. Each 15 minute session the throttle positions when up. First under 1/4 throttle, 1/2 throttle, 3/4 throttle, and then i gave her a good run and worked her hard.