Cliff
Compare your dry test numbers to the manufacturers specifications. If they are
considerably under the specs. THEN do the wet test.
A dry test can also tell you: that you might have a faulty head gasket if two
adjacent cylinders have low readings, or if the pressure builds up erratically
(as you crank the engine) the problem could be burned valve seats or sticky
valve guides.
A wet test is done to help diagnose WHY your compression is low, it is not done
to confirm low readings on the dry test.
e.g. On a wet test, if the compression increases to nearly normal then the
rings, piston, and cylinder (for that cylinder) are probably in need of service.
If the pressure does not increase then the valves are probably in
need of service. In this case the numbers would be in your friend's words
"fairly consistent" with the dry test readings which might cause you to miss
diagnosing the valve problem.
That's my understanding of compression tests.
Bud 71TR6 CC57365
____________________Reply Separator____________________
Subject: compression test procedure...
Author: Cliff Pike <cpike@mgl.ca>
Date: 11/3/98 4:23 PM
Listers:
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?
TIA
Cliff Pike
Guelph, Ontario
'58TR3 TS307677LO
'66 Spitfire4 MKII FC85163
'66 Spitfire4
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