how do i check cylinder compression?

[dignthewoods]

Trying to check cylinder compression on my '07 xcfw 250 and not having much luck. is there a particular procedure for doing so? thinking the automatic decompression mechanism must be engaged as getting next to no reading on the gauge. ?

i've warmed the engine up, pulled the fuel tank, air filter, and plug, installed the gauge and turned the motor over with the electric start while i hold the throttle fully open.

i must be missing something as getting no reading to speak of...gauge needle flickers up to about 25 and then immediately drops back to zero.

bike runs fairly well but thinking i'm about due for a piston and rings...thought i'd check compression! seems obvious thing to do...

what am i doing wrong here?

[wrsm]

You are ding the correct procedure. Maybe you have a leak on the adapter or gauge as it should lock onto the highest pressure, not drop down? I got 90 psi cold.

[dignthewoods]

thanks for your reply. wondering about a leak in the gauge, or something like that, as well. though, borrowed it from a reliable source. how do i defeat the auto decompression? thinking may not be holding compression in the cylinder if not defeating the auto decompression...?

Edited July 10, 2011 by dignthewoods
got ahead of myself

[dignthewoods]

so here's the resolution...

guessing ktm never intended for compression checks to be completed on the bike as automatic decompression on start up prevents same... that is unless you're persistent...

we removed the valve cover and temporarily jammed a small wood splinter in the auto decompression mechanism thereby disabling it. we were then able to secure the desired reading...

well, i say desired... appears evident i'm due for at least a set of rings... with the auto decompression engaged, i couldn't get a reading higher than 25. with the splinter in place the reading only jumped up to75-80, or so.

and so far as the flickering needle on the gauge goes...turns out the needle valve in the end of the gauge that goes in the bike wasn't working correctly. so figured that out too...

from reading around a bit i gather the wiseco (sp?) piston and rings is the way to go...even preferred over the actual ktm stuff?

[jar944]

The big bikes get 115psi with the auto decomp working correctly. I've never heard of anyone disabling it for a compression check before.

[loopsrider]

Do a leakdown test. Best judge of engine health anyway...

[William1]

+2 on the leak down. Only accurate way to test.

[etrain]

+2 on the leak down. Only accurate way to test.

do you recommend one that adapts to the spark plug hole?