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Compression test: What does it tell me

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F

Flagstaff

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I just did a compression test on my '63 Sprite.

What prompted the test was a white or gray smoke coming from the tail pipe.

Cylinder #1 was 140 psi
#2 was 130
#3 was 135
#4 was 135

I might say given the above that the plug from #1 looked the most fouled which was consistent with the first time I checked the plugs and clean them all

Thanks for any input
 
Supposed to be within 10% or each other. Some say 5-10 psi of each other.

How long has the smoke been present/car been sitting?
 
The car was sitting for a month and a half that I had it. Think it sat some time before that because I had it hauled to me by truck. Baby has only been out once for about a 10 min. drive.
 
I think the compression results are fine and suggest that your engine is relatively healthy (i.e. apparently not in immediate desperate need of a valve or ring job.. As to the white smoke, that might be a leaking head gasket or any number of things that won't show up in a compression test.
 
Fuel and oil were in the car when I got it. I will take care of those first off.

Thanks for the replies. Gives me somewhere to go.
 
On a non A-series engine I recently did a compression test and everything looked "OK" percentage-wise from cylinder to cylinder (like yours) but my readings were much lower. I knew something else had to be wrong so I brought out the leak-down tester and quickly found that cylinder #2 had some form of leak into the cooling jacket (crack, head gasket, who knows). Anyway, the reason I bring this up is to point out that a leak-down test may show you things that are wrong that won't show up in a compression test.
 
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