BannedCR500Riders.com

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.

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.

CR500PHIL wrote: 145-150 PSI. is this reasonable?

sounds good to me.

Roostius_Maximus wrote:......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!

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.

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

seanmx57 wrote: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.