compression check help

[afroman]

i did a compression check on my EXT 580 with a new gage i bought. both cylinders read about 110 psi but they both would not hold the pressure (both drop to zero within 30 sec.). is this a problem with the motor or the gage? my buddy said i probably have a leak in the crank gasket and i should check by spraying WD40 around the gasket and if it idols up the i have a leak. i tried the and i didnt idol up. the sled runs fine and idols fine. why wont the comp. gage hold?

[wildirishrose]

Is it possible that when pulling the motor over the piston is coming down and releasing the pressure out the exaust valve? Don't know, just an idea.

[afroman]

i was thinking the same thing. so how do you get the cyl. to stop on the comp stroke so everything is sealed. just keep trying or is there a trick?

[norm]

The problem is in your gauge. Check all the connections for leaks but you most likeley have a bad schrader (sp?) valve. Its the valve in the end of the hose and it looks the same as the valve in your bicycle tire. Just tighten it up or replace it and you should be good to go.

[rmh2o]

I would agree with Norm the gauge is bleeding off but it is still reading the compression OK.

Afroman your sled should be fine now,I will guarantee you that your problem was dirty carbs.Even when you take apart the carbs and they look clean inside it only takes one spec to screw things up.

[lawdog]

Hey fro, I wouldn't worry. I think the others are right it sounds like the gauge, and besides that, if you cleaned the carbs and its running real good now, you don't have a blown cylinder...

[Macgyver55]

I replied in your other post about (bogging 580) too but here again. The gauge is definetly the problem. It should hold whatever PSI that is pumped into it. Most have a schrader valve (like a tire valve style) or a small button to release the pressure after reading it, but it should hold for several minutes without a problem.

Any used cylinder on a motor will leak down some percentage of its compression. If that percentage becomes too high, thats when there is a problem. You can do a "leak down" test if necessary, but if you have 110 lbs compression I doubt you have anything wrong.

[afroman]

thanks for the replys. i guess i'll take the gage back and get a new one.