Let's Talk Compression

[CR500PHIL]

My 1989 CR500 engine I have in my AF (which I will post pics of when it is done) is freshly rebuilt. You can still see the the hone marks (cross hatch marks) in the cylinder from the fresh bore. I did a compression test and it is 145-150 PSI. For "unseated" rings is this reasonable? What would a "solild" "broken in" CR500 engine run in terms of compression? My AF project is running longer than expected - thanks to the taxman but I am taking pics and they will be posted when I am done.

[Roostius_Maximus]

i'd do a leakdown test, i hold the compression test as irrelivant for the ring package. Check it and it will tell you the % of leak past the rings instead of what port timing, gasket and other varriables have changed your compression to.

[south central hoon]

145-150 PSI. is this reasonable?

sounds good to me.

[AlisoBob]

......instead of what port timing, gasket and other variables have changed your compression to.

Yup....

When you do any machine work or porting... do a compression check the day after your first ride and record this number.

Then later, when doing subsequent compression checks... you need to be within 90% of this recorded number.

Changing exhaust timing changes your own "healthy" compression check numbers... ALLOT!

[100hp honda]

ya what bob said. if you raise the exhaust, your cylinder pressure will drop substantialy...to gain it back you have to shave down the head.

[seanmx57]

boring out them dam scallops to 90mm will bring some compression into the picture.

[CR500PHIL]

boring out them dam scallops to 90mm will bring some compression into the picture.

Mine is a fresh 91mm bore - perhaps less than 30 minutes run time on it yet.