I have a 1980 300d with a questionable background. Odometer says 156K, it works, but who knows if it's original, etc.. I have a lot to do to the car and I started with a compression test using the Harbor Freight diesel kit that was suggested on this forum. For starters I wanted to make sure the engine wasn't toast. It starts easily and doesn't smoke. But the condition of things under the hood didn't really match how well it started/runs.

The compression on the cylinders from front to back is 400, 350, 365, 360, 345.

Would anyone suggest checking the valves? With the compression that high I would be inclined to leave it alone, but I have been reading how important that adjustment is to the MB diesels. Is there a chance that the valve clearance at the camshaft may be too high and the valves are seating in too far(if that's possible) and giving me a false high reading?

Any thoughts or opinions would be appreciated. I am just getting started on learning the ins and outs of diesels. I'm just a shade tree mechanic.

Thanks!

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'80 300D na @156K
'82 300TDT Midnight Blue - Parts car
'84 300D euro 4 speed
'99 Isuzu Trooper
'67 Mustang GT 390/4 speed
'96 F350 Dually Dump (For Sale)
'00 Kawasaki KLR650

as the seats wear, the clearance to the valve lash is reduced, causing the compression to leak down on some cylinders. the low cylinders are most likely showing you the reduced lash. 400 is great compression, was that cold crank pressure, or running?
one thing you don't want on these cars is great pressure diff between cylinders. 55 and 50psi is a big drop on those cylinders.
I would go ahead and pull the valve cover off and get the valves adjusted and out of the way. then recheck the compression and see if it has improved on the low cylinders and I doubt the high ones will drop.
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
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Thanks VStech. It was cold and I took the reading from the glow plug holes and cranked it over 8 times on each cylinder. I'll check the valves when I get a shop manual and valve cover gasket, and the freetime. I'll post results, but it may be a while.

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'80 300D na @156K
'82 300TDT Midnight Blue - Parts car
'84 300D euro 4 speed
'99 Isuzu Trooper
'67 Mustang GT 390/4 speed
'96 F350 Dually Dump (For Sale)
'00 Kawasaki KLR650

Check the compression again hot. Should bring them up some.

As vstech says, check and adjust the valves.

If it was stored for a while, or if the previous owner didn't drive it much, the rings might be sticking a little also. My fix for that is to run a quart of Marvel Mystery Oil in the crankcase on oil changes and to drive it. If the rings are indeed sticking, that should free them up.

I wouldn't worry too much about those compression readings as long as it is running good, although valve adjustments and oil changes should be part of your normal routine maintenance. I'd drive it.

Good luck with it.

Wes