Checking compression on the top end?

[JEEP FARM]

Hey guys,

I am putting my bike back together after a winter overhaul. I don't have the exhaust on yet and tried to see what kind of reading I would get on the compression gage. I didn't get any reading. So I'm guessing I need to put the expansion chamber back on it first eh?

I just don't want to put it all back together and then find out that I should have done the top end.

I will appreciate any advice anyone has to offer!

Thansk, Jay

 

[_JOE_]

What exactly did you do to "overhaul" the bike? That should be item #1 on an mx bike.

 

[ZOMBIE666]

the fatty on or off wont change compression reading. either ur tester is leaking, u have a bad head gasket or the rings arent sealing

 

[2strokerfun]

You won't get an accurate reading unless the bike is warm, but you should still get a reading. Even with bad rings and leaking head gasket, I'd expect some sort of reading.

 

[JEEP FARM]

Well Joe I do the samething ever off season. Rebuilt the suspension, wheel bearings, suspension linkages bla bla bla!

I put a top end in it last summer but just wanted to make sure it was still all good! I have never checked the compression to see if it needed a top end before. I usually just do it and every time I do, I really did need to. So this time I figured I would try it out.

I also heard that I need to hold the throttle open, is this true?

 

[JEEP FARM]

Ok guys,


I just tried it out again. I held the throttle wide open and at the same time kicked the **** out of it. I ended up with max 152 PSI. That is also after sitting in my basement all winter. If it was HOT I would guess it would be around 170-180 PSI?

Do you think it's ok or worth tearing into? I might just wait and do it again later when I get it fired up and hot!

 

[_JOE_]

I would say if it's a year old it's at least worth a look. If you're gonna pull it down you might as well replace the rings if the piston is still good. How many hours do you figure are on the top end?

 

[Reesknight]

I checked mine a few days ago and it said 215 PSI, cold. That's with the original piston/rings still in it(low hour bike), but its a cheapo pressure guage so I'm not sure how accurate that is. I think 152 sounds low tho.