Compression test procedure-using too much oil! - Team Camaro Tech
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post #1 of 5 (permalink) Old May 23rd, 01, 12:30 AM Thread Starter
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Location: Benicia CA
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I have done compression tests before but want to make sure I am really doing it right.
(Did a serach but didn't get a clear answer).

Do I do the test with the engine warm or cold?

When warm, I get ~165# across the board.
If I try it cold, I get next to none! The reading drops almost immediately. Can't get a good seal with the gauge when cold?

Should I do the oil in the cylinder test when cold? Or could the pistons and rings need to be warm to seal?
I am using a lot of oil and the plugs are fouling badly. I am pretty sure my valve seals are gone from the smoke at start up and decelleration. It also will smoke when I get on it hard, but only if it's been running at low speed or idling for awhile. Then it stops smoking.

Could the fouling and smoking be primarily from valve seals?

I'm planning on rebuilding this winter, but if I could slow down the oil use by replacing seals, I'll try it.

I have a crankcase evac system to the headers and the hose is pretty oily so I think I'm sucking oil out as well.

I have about 90# of oil pressure, so I think I'm flooding the valve seals too.

Sorry for the long post but wanted to get the facts out.

Thanks in advance!

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post #2 of 5 (permalink) Old May 23rd, 01, 01:05 AM
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Go ahead and try the oil in cold cylinders, certainly can't hurt. It will boost the comppession.

If you can use a cylinder leakage tester, this is a better instrument to use. It tells the percentage of leakage and where the combustion chamber is leaking from.

Turn cylinder to be tested to compression TDC
Use shop air at 100 psi on the inlet, then then read the gauge to see how much leaks off, i.e., 100 psi in, gauge reads 88 psi, leakage is 12%. While air is in cylinder, listen for leakage at intake manifold, exhaust manifiold, and/or oil fill cap for seepage thru rings.

As far as oil in evacuation tube, and with 90 psi pressure, be sure to have cap on valve cover to be baffled on the inside. Lots of oil spray inside covers.

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post #3 of 5 (permalink) Old May 23rd, 01, 02:51 AM
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It sounds like you have blow by on the rings which will smoke when you get into heads shouldn't do that.I've always done compression tests well cold with throttle plates wide open.Is this an older engine or fresh?What kind of rings are you using?I used low tension rings this year and am having some problems with blow by.They are starting to seat now and some hard runs at the track but I'm still using more oil than I would like.
90psi is high as well espicially if it's warm with that kind of psi.
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post #4 of 5 (permalink) Old May 23rd, 01, 03:07 AM
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Joe if the motor has 165lbs straight across when warm it is fine. Something in your testing procedure is wrong when it's cold. they don't vary that much. If it didn't have any compression when it was cold it wouldn't start.

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post #5 of 5 (permalink) Old May 23rd, 01, 07:40 AM Thread Starter
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Oger, I think I'm doing something wrong when cold also. I have the screw-in type of gauge and can't seem to get it to screw in well when cold for some reason. When I turn it over the pressure comes up, but drops back very rapidly. I think back through the threads. I'm going to get a pushd-in type of gauge and try again. Just takes 2 people to do it that way.

Cragger, the 90+ pressure is when warm; idles at 3-40 when warm. Too much!

Age and mods of engine is unknown. "Supposedly" less than 8000 miles on engine. It does run real hard!
Spins up easy to 6000 rpm, but I try to not do that too much!

There is also some "rattling" when it's cold. I think this is piston slap or rocking. Goes away as it heats up. Not a rod knock or lifter sound, but in the middle, if that makes sense.

When I disconnect the evac tube I get some oil dripping out of the breather after a while, but not really any visible blowby vapor. That's contributing to my confusion.
I'm planning on going thru the motor this winter, but would like to keep using it until then. I'm finding that I'm driving it almost daily when the sun's out.



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[This message has been edited by Joe G (edited 05-23-2001).]

[This message has been edited by Joe G (edited 05-23-2001).]
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