On Tue, 3 Nov 1998, Cliff Pike wrote:
> Progressing slowly with TR3 TS30767 frame up rebuild, which brings me to
> the engine. An ex-military diesel mechanic friend tells me that a proper
> compression test is done in two stages: 'dry' and 'wet'. The dry test is
> done before adding oil to the cylinders, Record the numbers, then add
> oil and test again. According to him, if the numbers are fairly
> consistent during both tests then the engine is in good shape. If the
> 'wet' test indicates higher numbers, then there could be a problem.
> Anybody like to comment?
Yes, this is true. If you get consistent numbers then the engine is
probably OK. If you get consistent low numbers (for both tests) then the
engine is OK but the valves are worn. If you get low #s for dry test and
high #s for wet test then your engine is OK but the rings are worn (or
stuck)
If you get inconsistent numbers then you have a slightly worse problem;
having one weak cylinder is harder on an engine than having all weak
cylinders. The oil gets into the bore of the cylinder and makes a better
seal around the rings. You should see a slight increase in compression
(not a lot) with wet vs. dry tests.
My engine came out with quite low readings when I last did a compression
test. However that was before I adjusted the valves, and the engine was
cold.
I want to do another test with a hot engine and my (Now-adjusted) valves.
Compression numbers will vary depending on your compression ratio,
relative height above sea level, quality of compression tester, patience,
phase of the moon, brand of coffee you drink, etc. The key here is to
have all numbers within 10% of each other. (all between 110 and 120 is
fine, between 100 and 125 not so good)
-Malcolm
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