PeachParts Mercedes-Benz Forum - View Single Post

tcane · #4 02-13-2002, 03:10 PM

A wrist pin/piston pin knock is heard more clearly in the upper area of the engine in the water jacket area of the cylinder at issue. A big end rod knock is heard more clearly in the oil pan area. To test bring the engine up to about 2,500 RPM for a very brief moment, snap the throttle full open and release it fully, a wrist pin knock will sound about the same, and a big end knock will usually get louder. Loosening the injector line will usually reduce a wrist pin knock and a big end knock will get worse. Good oil pressure at idle usually indicates the crank/rod bearing are OK. Listen for sound using an engine stethoscope, a screwdriver with a long shank, or a piece of wood.

Your info sounds like a wrist pin knock. Use the above test to narrow it down. M-B diesel wrist pins are very tight: non-turbo engine .0005 to .0009 inches or .012 to .023 mm pin to rod clearance, and .0000 to .0039 inches/.1mm for the pin to piston clearance; turbo engine .0007 to.0011 inches or .018 to .029mm pin to rod, and the pin to piston clearance is the same.

Good Luck!
Tom