[Vwdiesel] Compression testing for beginners.

[James Hansen]

Thanks Hagar, that's a good read.
-James

-----Original Message-----
From: vwdiesel-bounces at vwfans.com [mailto:vwdiesel-bounces at vwfans.com]On
Behalf Of H . Hagar.
Sent: Saturday, December 11, 2004 2:48 PM
To: vwdiesel at vwfans.com
Subject: [Vwdiesel] Compression testing for beginners.


CP63-P7           Look up on net.



    If you have an abnormally low cylinder, you should start the engine and
run it on the ground or even fly around the pattern once. Test it again. If
it is still low, use a length of garden hose as a "stethoscope" and listen
at the exhaust of the ailing cylinder. If you hear a hissing escape of
compressed air here, you have an exhaust valve that is not seating.
Similarly, listen carefully with the "stethoscope" at the carb or intake
airbox. A hissing sound here would indicate leakage under the intake valve.
If neither of these areas is leaking significantly, listen at the breather
or oil dipstick/filler tube. A leak in this area is indicative of ring
blow-by. This could be ring wear, barrel wear or scoring, or all the ring
gaps may be lined up. Hissing between cylinder cooling fins is bad news,
possibly a cracked cylinder. Valve leakage is the most commonly found cause
of a low cylinder.
     The differential compression test has its limitations but it still
remains one of the best, most cost effective preventive maintenance
procedures available to the builder/flyer. The method described here is
simple and it works. Done every 100 hours regularly, you could save big
bucks in the long run.
     If you would like to learn more about this procedure and many other
cost saving tips for keeping your engine in good shape, you could not do
better than to obtain a copy of "Top End" from the Light Plane Maintenance
Library.
Write to: Light Plane Maintenance
1111 East Putnam Ave.
Riverside, CT 06878

Hagar.







  A single compression test does not necessarily mean anything. A single oil
analysis also means very little. No single diagnostic test should ever be
used to decide the health of your engine. The key is to do these tests
regularly and keep good records of what you see. Compare each test and make
your decision based on several tests conducted over a reasonable period of
time.
     If you have an abnormally low cylinder, you should start the engine and
run it on the ground or even fly around the pattern once. Test it again. If
it is still low, use a length of garden hose as a "stethoscope" and listen
at the exhaust of the ailing cylinder. If you hear a hissing escape of
compressed air here, you have an exhaust valve that is not seating.
Similarly, listen carefully with the "stethoscope" at the carb or intake
airbox. A hissing sound here would indicate leakage under the intake valve.
If neither of these areas is leaking significantly, listen at the breather
or oil dipstick/filler tube. A leak in this area is indicative of ring
blow-by. This could be ring wear, barrel wear or scoring, or all the ring
gaps may be lined up. Hissing between cylinder cooling fins is bad news,
possibly a cracked cylinder. Valve leakage is the most commonly found cause
of a low cylinder.
     The differential compression test has its limitations but it still
remains one of the best, most cost effective preventive maintenance
procedures available to the builder/flyer. The method described here is
simple and it works. Done every 100 hours regularly, you could save big
bucks in the long run.
     If you would like to learn more about this procedure and many other
cost saving tips for keeping your engine in good shape, you could not do
better than to obtain a copy of "Top End" from the Light Plane Maintenance
Library.
Write to: Light Plane Maintenance
1111 East Putnam Ave.
Riverside, CT 06878
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