Kx 500 compression test

[brad75raiders]

I have a new to me 1997 KX500 aka "the green machine" I have a dyno pro pipe stock spark arrestor with unknown engine mods. The Older gentlman I bought the bike from was the 2nd owner. To his knowledge the top end has never been gone through!??! So my question is this, What should "cold" compression be on the motor.  The bike runs kick ass now with a 14 oz. flywheel weight {hills} Just wondering If I am sitting on a time bomb. How long for/inbetween rebuilds and what should compression be at, wore out and rebuilt. Thanks for your time.

[climber05]

I think my fresh motor kicked 90psi cold and the guys at the bike shop said that was a little high. If your bike is jetted well you should beable to take the top end apart every 100 hours and brake the glaze in the cylinder with a honing stone and replace/regap your rings. I think you can do that a number of times. I would recomend doing it sooner rather then later it will avoid a top end melt down. If the bike has run good this long it will most likely just stop making good compression one day in the middle of a ride and then youll know. The rings are birt cheap I would also do a piston for what its worth I like the pro x myself. Hopefully kawrider or motorrad will chime in for you there knowledge is highly indepth.

[brad75raiders]

I forgott to add my bike is at 140lbs cold now.....

[Suva]

mine had 152psi cold just before I took her apart for a rebuild... 

[climber05]

Ya now that I think about it 90 psi is all I could get because im 170lbs. My 300 lbs roommate through a boot on and he kicked it 150psi cold.

[brad75raiders]

thanks for the responses. I will prob ride this weekend then start the tear down and fing out if my bore is std or overbore and if I need a re "coat".