Checking compression...

[edz250r]

Hey guys...I recently had my 250r topend rebuilt with new piston, porting and esr head with 21cc dome and CR gasket. I was told by both esr and the builder that this would get me about 185psi. I just did a compression check with throttle wide open and I'm only getting about 140-145psi. I called my builder and he said that I wont get an accurate reading if I'm using the kind of compression gauge that has the threads on the end with the rubber o-ring since the o-ring doesnt give a good enough seal for pressure over 140psi or so. Have any of you run into this same problem with the o-ring and not getting the psi you really have? My only other thought is that the right gasket wasnt used, but esr confirmed that they only include the cr vs oem gasket in their head/dome kits.

[wilkin250r]

You also may not get a good reading before break-in, because your rings aren't seated very well.

The length of hose running to your actual pressure gauge can affect your reading.

If I were you, I would try to find a friend or relative with a pressure gauge, and compare readings. Calibrating your pressure gauge will be a lot easier and less expensive than rebuilding your top end all over again. Check the easy things first.

[edz250r]

Thanks, wilkens. ESR told me that they thought I should still have more compression even before I break it in, but I agree with you that it might not be seated very well. I'll borrow a friends gauge and see if I get a different reading.
I was revving the motor a bit in neutral the first time I started it, but not wide open. Do you think I could have glazed the rings and messed it up???

Anyone else have problems getting an accurate reading with o-ring seal compression gauges?

[wilkin250r]

Originally posted by edz250r
I was revving the motor a bit in neutral the first time I started it, but not wide open. Do you think I could have glazed the rings and messed it up???

Anyone else have problems getting an accurate reading with o-ring seal compression gauges?

I doubt revving the motor in neutral caused any problems.

I've heard of people having problems with some styles of compression gauges. Try a search.