After putting 10,000 mi. on rebuilt heads,i just did a compression test and these are the results:#1=178 #2=180 #3=175 #4=185 #5=183 #6=175 #7=168 #8=183 I don't know what it should be with 175,000mi. but # 7 seems too low in comparison to the others.Is this normal wear of the rings/cylinders or are the valves not adjusted correctly? Sorry i don't know what the compression was before the heads were rebuilt.I had a blown head gasket that was leaking oil.

hi

you have a 15 pound spread. 10 is perfect so you're ok. if you had say 175 on 5 cyls and 110 on 1cyls then i would be looking into why.

IMHO slam the hood, turn the cd up, plan a vacation and go!

tks
craig

__________________
Thanks Much!
Craig

1972 350sl Red/Blk 117k
1988 420sel charcoal/Blk 140k
1987 420sel gold/tan 128k
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Old enough to know better but stupid enough to do it anyway!

Try A Leakdown test (WARM) It Will Help you determine where The Problem is ..IF There is a Problem!
A Leakdown test Will Tell You On What Cylinder The Problem is..if any..Be It a Intake or Exhaust valve or Piston Ring

Thanks guys. Mark How does one do a[ leak down test].

If You Have Never done a Leakdown Test..I Would Have a GOOD MB Shop perform it

With a WARM Engine
You Will Need a Air compressor
The Leakdown Testor...
Remove all Spark plugs
Rotate each Cylinder to TDC and Screw The Hose to the testor into the spark plug thread and Hook up Supplied air (Air Compressor) and The Difference between the Supplied air and Your Reading on the Leakdown Testor is the Difference in Percentage. of Leakage .then Listen For any leaks...Listen at the rear muffler for Exhaust valve Worn/listen at the Intake for a Intake Valve worn/With the Oil cap off Listen for Defective Rings...
Chances are You Will NOT have a Problem...With The Readings You posted...They are In The Ball Park

You can also squirt a small amount of oil into #7 and redo the compression test. If the results are higher, it's rings. If it's not, it's valves or head gasket, or a crack in the head.

Gilly

I'd still question whether there's actually a problem at all; for a 175K car those numbers sound pretty good to me. If MB should run significantly tighter than these results, I'd be eager for one or another of our valued gurus to shed light on appropriate standards.

__________________
Craig Bethune

'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)


SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)

I did the test with all of the plugs removed.Can i re-do #7 by removing only that plug? P/s rember both heads were just rebuilt.

You "could" do it that way, but the engine won't be spinning as fast, so may not be a fair test. If you do it that way and get a better reading, I'd trust it. If you get the same or a lower reading, I wouldn't trust it.
I agree it's not different by much. What does the manual say about permissable difference between cylinders? (I'd acknowledge here that afmcorp "craig" already mentioned this)

Gilly

Gilly: I don't have a manual,but i looked through the search threads and could not find anything about acceptable numbers.

MB lists "normal" compression as 8.5 bar, "low" compression as 7.5 bar, and maximum difference between cylinders as 1.5 bar.
Using this site:
http://www.ex.ac.uk/cimt/dictunit/ccpress.htm
it converts to the following:
Normal 123 psi
Low 109 psi
max difference 21.8 psi

So yours is better than normal and max dfifference is good. They don't list a "new" spec for this engine.

Gilly