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Additional stuff Posted by Ari [Email] ![]() ![]() In Reply to: Re: Compression test- step by step procedure?, JimBlake ![]() ![]() |
Pretty much what Jim said, with some additions-
Note the reading after the first compression stroke. Note the reading after four compression strokes (including that first one). I don't recommend using the reading after the forth stroke. This is called the 'dry' test.
After doing this test in a cylinder, drop in about a teaspoon of motor oil. Turn the engine over a couple/three times. Repeat the test. This is called a 'wet' test.
Now - interpretation-
The compression reading after the forth stroke on the 'dry' test is the compression number generally used. The lowest cylinder should be no less than about 80% of the highest cylinder.
First compression stroke reading on 'dry' test to final dry test reading - The first stroke should be at least 75% of the final reading. Low reading? Indicates an issue with rings on the compression stroke.
If the 'dry' test readings look good, the 'wet' test is not required. If one or more cylinders are low, compare the fourth compression stroke of the wet test against that of the dry test. A rise of 10 psi or so is normal.
If a cylinder compression is low dry, but increases to almost normal 'wet', then ring/cylinder wall issues are indicated. The oil acts as a sealer. If there is no change, then it's more likely valves. Of course, on an old engine, probably both are at work.
posted by 192.249....
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