PeachParts Mercedes-Benz Forum - View Single Post - 1980 W116 300SD OM617 Front Crank Seal Replacement

Squiggle Dog · #7 02-10-2013, 12:15 AM

A new crank bolt (grade 10.9 pictured) and cupped washers should be used because of the high amount of torque to which these are tightened, and the potential for breakage due to vibration. These are to be installed with the threads lightly greased and tightened up to 270nm or 200 ft-lbs. I do not have a torque wrench that goes this high, so I rented one for free from my local auto parts store. You'll need to use an extension wedged in the balancer to tighten it up this much. I placed a rag around the extension so it wouldn't dent the upper oil pan. 270nm is a lot of force (sometimes it looks like you are lifting the engine out of the car). It's best to pull the wrench toward you as you tighten, making sure to not let the socket on the crank bolt slip.

I used 80 grit sandpaper on the belt surface of all of the pulleys while they were off, making perpendicular lines to discourage belt slippage.

Crank pulley screws should be used only once. I ordered new ones. The originals were grade 8.8. The replacements are grade 10.9. Supposedly the early engines used grade 10.9 and a bulletin was put out to replace them with 8.8 because they had a tendency to shear off. Now I see Mercedes went back to grade 10.9. I would not recommend using grade 12.9 found at the hardware stores because even though it is a higher tensile strength, it is more brittle than a grade 10.9 or 8.8. I would recommend using grade 8.8 if available. I ordered new spring washers, but since January 1979 they were no longer installed on OM617 engines. I used blue thread lock compound on them and tightened them to 30nm (25nm is spec for grade 8.8, I went a touch higher due to higher grade screws plus 25nm didn't seem tight at all).

I had a nice-looking spare fan clutch, so installed it.

I put the radiator shroud, fan, and belts back into place. After things were tightened up, I started the car and let it run for a while. So far, no leaks! It seems my repair was a success. It's one that I had been dreading and I think it went rather well. It only cost me about $50 and several hours of time. I'm sure this would be an expensive job to have a shop do. Let's hope my rear crank seal and upper oil pan hold up for a while!