100 psi compression good or bad?

**FJRider** · 19th October 2012, 16:11

Originally Posted by grotto

It's on a bike I was thinking of buying.
39,000 km on the clock, starts & runs real good.
I couldn't find manufacturers spec of what compression should be.
I didn't have throttle wide open (forgot). Would compression be higher or lower with throttle wide ope?
Thanks

What size/model engine ... ??

**SMOKEU** · 19th October 2012, 16:23

Originally Posted by Katman

Comes between O and Q.

WTF do you know about O and Q?

**neels** · 19th October 2012, 16:49

Originally Posted by FJRider

carry spare oil

On a 4 stroke, only if the oil ring is leaking, if the compression rings or valves are buggered it could have low compression but not burn any oil. It will, however, blow out the crankcase breather like crazy.

100psi cold is probably not too bad, run it and get it hot and take off the engine breather or if too hard the oil filler cap, if it's puffing like a steam train the rings are sad.

**FJRider** · 19th October 2012, 17:00

Originally Posted by neels

On a 4 stroke, only if the oil ring is leaking, if the compression rings or valves are buggered it could have low compression but not burn any oil. It will, however, blow out the crankcase breather like crazy.

100psi cold is probably not too bad, run it and get it hot and take off the engine breather or if too hard the oil filler cap, if it's puffing like a steam train the rings are sad.

It could be the valves fucked as you say ... wont blow smoke ... just wont pull.

I haven't seen what size engine it is. On a smaller one ... 100 may be ok ... sort of ...

To follow it and smell the fumes ... if there is a small amount of "burning" it would be noticed then. I had an XJ750 that did that. It went ok .... but (and) used oil by the gallon.