Rock'n'roll 300D

[psfred]

I have just aquired a 1987 300DT with what I suspect are major engine problems. Symptoms are:

hard shake at idle, no power below 2000 rpm, miss at speed. Compression test indicates marginal (300 psi) compression in most cylinders, # 4 lower. #4 appears to be nearly dead at idle, #2 and #3 also low on output. A leak test shows leakeage past the rings into the crankcase. Valves show minimal leakage.

The radiator is new, leading me to suspect a failure and severe overheating.

Does anyone have any experience with such conditions in a 603? Is there anything I can check before starting a complete rebuild (I will be doing this myself)?

I have searched all the listings I can find, and have the following ideas:

Cracked head -- the car runs cool and doesn't appear to have any exhaust gasses in the coolant, nor coolant in the oil.

Stretched chain and bad chain tensioner -- could account for the poor compression, but what about the leakage down the cylinder walls?

The motor oil is VERY thick -- my brother suspects "motor honey" plus probably 50 wt oil (like his 75 300D -- another story). This would explain the lack of oil consumption (hasn't used any in 1600 miles).

I plan to check the chain and change the oil this weekend -- if the rings are just stuck I suspect Mobil 1 will free them up. If the cylinder walls are shot, it will smoke like crazy when I put decent oil in it.

Thanks in adavance!


Peter

[stevebfl]

If all cylinders are close to 300psi compression, I would not worry about engine mechanicals as far as performance is concerned. I would look to pump or injector problems.

[psfred]

Steve:

Thanks -- I initally suspected fuel delivery problems, too, but today I found some oil in the coolant pressure tank. At the very least, I have a bad head gasket, more likely a cracked head, I suspect.

When I get a chance to get this thing indoors (need to finish the resoration on my brothers 75 300D first) I will yank the head and take a look-see.

I gather that the 603 has a reputation for cracked heads when overheated. I have no idea what the service has been like on the car since 93 when the second owner sold it -- no records past that in the MB service book.