Compression Testing

[daveymc29]

So now that I'm well schooled on how to torque the heads, what's the proper procedure for a compression test? Hot or cold? In the past I have usually done them with the engine warmed to normal operating temperature, but circumstances have sometimes dictated that the only way to test it was cold. So which is proper? I have not noticed a remarkable difference when testing the same engine hot or cold.

[Patrick L.]

I don't think it much difference either whether you check it hot or cold. The concern is how close each cylinder number is. I don't really worry too much about how high the numbers are, gauges are not all created equal.
Just make sure all the sparklers have been removed, each cylinder is spun over about the same number of times and pay attention to the first and last needle reading. The throttle is supposed to be open, but, that really doesn't make much difference either.
Consistency of the readings is what matters.

[Mike V. Florida]

This is from an ASE master mechanic
,

1 Engine FULLY warm.
2 Throttle WIDE open.
3 Battery FULLY charged.
4 Crank it at least 10 strokes, or until gauge no longer rises.
5 If one is low, retest it several times, as carbon may be stuck under a valve from taking out the plugs.

[Bob Bidonde]

A compression test should be SOP and the first step for every tuneup. Mike V has the right procedure in the post above, but take out all of the spark plugs before doing the test.

A compression test will indicate low cylinder pressure. In my opinion, cylinder pressure should be 55 to 75 psig for the stock compression ratio. The difference between cylinders should not be more than 3 or 4 psig. Each cylinder should be able to hold its pressure for a few seconds.

[Jim Brierley]

warm, and i only do 4 spins.

[Tom Wesenberg]

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Originally Posted by Jim Brierley

warm, and i only do 4 spins.

I do the same. 4 spins is enough to tell the story.