Compression Test

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Sep 5, 2005 | 06:07 PM

STL94LT1

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From: O'Fallon Missouri

Compression Test

I did a cold engine compression test on my car today. What is an acceptable variance from cylinder to cylinder?
Results:
1. 215
2. 205
3. 220
4. 200
5. 220
6. 220
7. 200
8. 200
I hurt my car on the dyno Saurday. #3 exhaust lifter was damaged, and #8 exhaust pushrod was bent/broke. Just trying to fiqure out if there is any more damage. Going to scope the cylinders tomorrow.

Anything else I should look for?
-Mike

Sep 5, 2005 | 06:10 PM

Pete K

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Quote:

Originally Posted by STL94LT1

You are within 10%. I believe 20% or less is exceptable. A leakdown test will tell the rest of the tale.

Sep 5, 2005 | 06:11 PM

Pete K

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I just noticed you did the test cold. Warm is better. Also, i always hook up a battery charger while doing the test. Kepps the voltage up so I cranks consistanyly throughout the test.

Sep 5, 2005 | 06:13 PM

STL94LT1

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From: O'Fallon Missouri

Pete, the car is tore down because of the damage I did Saturday. I'm just trying to find any other possible damage before I put it back together.

Sep 5, 2005 | 06:17 PM

Pete K

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That is why I mentioned the leakdown test. If a valve is bent, even slightly, you will be able to pinpoint it. Leakdown will also reveal ring seal, gasket leakage etc.

Sep 5, 2005 | 06:19 PM

STL94LT1

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Quote:

Originally Posted by Pete K

That is why I mentioned the leakdown test. If a valve is bent, even slightly, you will be able to pinpoint it. Leakdown will also reveal ring seal, gasket leakage etc.

Thanks.

Sep 6, 2005 | 05:37 PM

DVNCI

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From: Bowling Green KY

So what happened? Why did she break?

Guess you might as well build a stroker now?

Sep 7, 2005 | 02:13 PM

STL94LT1

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From: O'Fallon Missouri

Quote:

Originally Posted by RUKWKR

So what happened? Why did she break?

Guess you might as well build a stroker now?

When I remove the rockers, I always reset the polylocks so that the lifters will be close during reassembly. Sunday when I reassembled the valvetrain to do the compression test. The rocker for the #8 exhaust valve was waaaay loose. My theory is: I hit the rev limiter at the dyno, and with an already loose rocker the pushrod worked it way loose, got in a bind and bent/broke.

I scoped the cylinder yesterday and doesn't appear to be any major damage to the piston, maybe not even piston/valve contact. Hope to find a leak-down gauge and test the affected cylinder in a day or two.