Been working on 2001 250 trailblazer. Been having knocking sound when hot. Thought it was clutch. Took to dealer and they said clutch was ok. After doing a compression check while hot bike only had 75 pounds compression. Can anyone tell me what the compression should be when its hot. Or should it be checked cold? If so what should it be cold? Thanks for any help.

 

115 lbs
Book didn't state whether hot or cold. Anything under 100 is bad news. It obviously runs though. Any chance of a bad compression gauge????

 

I am surpised it ran with only 75 pounds..........I second anything under 100 bad news ..Hot or cold
My comp. guage shows in the RED under 100 P.S.I.
............Caper.............

 

Gauge is old. I will check it . thanks for the help.

 

thanks 94harley. Bought new gage and retested. Got 115 so now I'm ruling out piston slap from my knocking noise. Going back to possible primary clutch problem. Took clutch now to dealer twice and they say nothing is wrong with it and button are good. I still think its the clutch because I can wobble it back and forth. I think maybe it's one of the inner bushing. They said nothing would make the knocking sound in the clutch other then the buttons.

 

I forgot this. Compression is created by the rings against the cylinder walls. Piston slap is caused by a worn cyl or skirt. You could still have compression from the rings and slap from the skirt.

One of the first 350's i ever did had 95lbs compression and the skirt was broken off and most of it was in the exhaust. Don't totally rule out piston slap.

 

is worn rings the only reason for lack of compression im gettin around 90psi this makes it really hard to start but seems to run ok

 

you still can have piston slap w/ good compression. ive seen bikes running at 90 psi but they dont have much power. make sure the gaskets are good as well. depending on the age, it might need to be bored and honed w/ new piston, and rings. imo.

 

<div class="FTQUOTE"><begin quote>Originally posted by: stendori

you still can have piston slap w/ good compression. ive seen bikes running at 90 psi but they dont have much power. make sure the gaskets are good as well. depending on the age, it might need to be bored and honed w/ new piston, and rings. imo.</end quote></div>

yep. What he said!

 

Well i had it bored 20 over. Bottem end was good. Now i still have the same knock. I know it has to be the clutch now. But what part could be bad? I have new buttons new bushings new spring. Rode my friends 06 and it is starting to make the same sound. Not as loud as mine though. This is always after riding 15 to 20 minutes. Does a clutch just go bad? thanks.