My compression test results are in and don't look pretty for cylinder #2 (OM617.952). Here are the numbers after idling motor to 80C and checking while block heater plugged in:

# ____compression, dry (bar)____pseudo-leakdown
1________23.8
2________13.8________________leaking at exhaust valve
3________21.4
4________21.4
5________21.0________________somewhat greater crankcase leakage

I verified that the valves were adjusted correctly (were done less than 5k ago), and these numbers are what I got. I didn't do a leakdown test, since I didn't have the tool, but I did pressurize each cylinder to about 40psi at TDC and checked for leaks at intake, exhaust, and crankcase.

It seems that #2's low compression is caused by the exhaust valve not sealing completely. Is this a sign of a burnt valve or could this just be carbon build-up? Is there a way to clear the carbon (if that is the cause) without tearing the motor apart?

I give her an "Italian" tune-up just about every time I drive her. The motor has 264k, has a hard time starting when cold, the exhaust has a prominent "chug chug" pulse at idle, and she smokes lightly. Could the smoke be caused by low compression at one cylinder?

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Dave

2002 Audi S6 Avant
1983 300D
1984 300D (sold)
1990 560SEL (sold)

compression and leakdown test will give you a better indication than a simple compression test. Which did you do?

ok I reread what you wrote....if you have clear signs of an exhaust leak and you have confirmed that valve clearance is in spec then you will in all likelyhood need a valve job.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

y'know, doing a head job isn't all that big a deal, and if you do the grunt work yourself, it's not even that expensive.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

tight and you adjust it, i would drive it for a while and see if it comes out of it. built up carbon could get knocked off and it may seal better. also i would adjust it agian after running it for a few weeks in case it seats a bit lower after the carbon wears off.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.