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Old 08-25-2008, 11:17 AM
dieseldan44's Avatar
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Join Date: Nov 2006
Location: Boston
Posts: 2,040
Question Help me decide if I should go for a rebuilt head..(OM617)


From an earlier thread trying to diagnose some loud idling, hard starting and nailing ( Need help with nailing / knocking / hard starts).

I tested my compression and found it to be:

(after a valve adjustment)
#1: 380 psi
#2: 360 psi
#3: 370 psi
#4: 220 psi (260 psi after squirt of oil)
#5: 250 psi (260 psi after squirt of oil)

I would think this points to valve problems. I have two questions:

1.) Pending a leakdown test to verify it is the valves, should I go for a rebuilt head from Metric? Is that the thing to do?

2.) Am I hurting anything driving the car with those compression numbers? It currently needs 10+ seconds of glow to start on the first crank without any misses, does 25 mpg and drives just fine. This car goes off the road in November for the winter, Id like to wait until then.


'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car
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Old 08-25-2008, 11:55 AM
Alastair's Avatar
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Join Date: Mar 2002
Location: South Wales U.K.
Posts: 1,064
Personally I would do a proper leak-down test first before deciding anything....

A fully re-built head will cost a few pennies especially from Metric (from what I gather,-based in UK...) It would be a shame to find it doesn't completely cure your issues....

Yup, Good hot engine, and leak-down test is best way forward and what I would do--It will tell you exactly where the compression is being lost....


Alastair AKA H.C.II South Wales, U.K. based member

W123, 1985 300TD Wagon, 256K,
-Most recent M.B. purchase, Cost-a-plenty, Gulps BioDiesel extravagantly, and I love it like an old dog.

W114, 1975 280E Custard Yellow,
-Great above decks needs chassis welding--Really will do it this year....
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