I though that I would follow up with this post and tell all that had helped me out what was wrong with my engine. I pulled the head to check everything out and it became evident what was wrong with my engine. You could rock the #2 piston in the bore easily and there were some scratches on the bore. I was lucky because it was the #2 piston, becasue I could drop the sump and remove that piston. I will try to post some pictures of that piston so that someone can tell me what would cause it to do what it did. The piston scirts are severely scored and the piston was worn to the point that you could slide a .020" feeler gauge beside the piston in the bore.

This was not the obvious diagnosis because the engine ran smoothly without blow-by. And this cylinder was holding 400 psi of compression! But it had a wicked knock that seemed to be on the #2 cylinder.

Well I got a new piston, honed the cylinder and put the engine back together. The skirt to bore clearance was within specifications, so that is a testament to how hard the cylinder walls are. The engine runs great, and I am now a happy member of the Mercedes Diesel community.

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1993 300D 2.5 Turbo (blue/ blue tex)
1991 350SDL (White/ Gray leather)
1983 300TD Turbo 5-speed manual (Green/ Beige)
1985 300SD (Black/ Black Leather)
1985 300TD (White/ Green Tex)
1980 300SD (Astral Silver/ Black Leather)
1990 560SEL (White/ Gray Leather)
1993 300SD (Black/ Black Leather)
1967 200D (Green/ Beige Tex)
1969 300SEL 6.3 (Moss Green Metallic/ Green Leather)
1975 300D (Astral Silver/ Green Tex)
2001 Ford Excursion Diesel