I broke the engine down last night. I took off the oil pan/intake and exhaust manifolds, expecting to find water, sand, in engine/like all junkyard engines. I was shocked! Engine was clean inside!!Oil was fresh. Stopped disaasembly at that point. No water or dust. Taking borescope shots today of pistons/ rings.
My intuitive feeling is that an engine like this is better left alone.Its a running engine. One could actually do more harm than good by rebuilding it unless one is a Mercedes pro because of the myraid specs and tolerances that must be done tediously when rebuilding.
I have a strong urge to (1) clean it, stop there and put it back together and run it. Car I took it from had approx. 150,000 miles.
or (2) Head Job, New Piston Rings/Oil Rings, Oil Pump What are your thoughts?

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Close all holes. Clean . Install new injectors and change oil and see what happens.
Good luck.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

I'd remove all injectors, fill each cylinder with a cup of lube oil, then manually turn the engine 720 degrees (2 complete revolutions) to lubricate the bores and rings. Have the injectors pop tested at this point.

Check camshaft and crankshaft alignment marks, and valve clearances too. I would also open the side cover of the injection pump and check the pump's control rack for freedom of movement.

Then hook up a battery and crank the engine for a few seconds (without the injectors of course) to expell out all the oil in the cylinders.

Install the tested injectors with new compression heat steel gaskets, and start the engine.

Good luck, our prayers are with you.