OM617 questions
 

Good morning guys, I am a newbie to the MB diesel world and have a few questions. Firstly, taking this engine/tranny out of my 1981 300SD was a bear (partially because I didn't really have any service manual or anything to follow, partially because of the previous owners lack of maintenance). When I bought the car it was running and driving but the radiator was busted so it was only for short little trips up onto a trailer or into the garage. The PO said there was a rod knock in the engine and while I could hear a tapping sound, it did not sound like a rod or main bearing issue. The oil pressure was rock steady at all RPMs, the tapping sound was at a mid RPM range (not at idle usually indicating main failure or at high RPM usually indicating rod failure). I am thinking my tapping sound is coming from the injection pump or the injectors themselves.

Either way it is pulled and after figuring out the puzzle of getting the OM617 mounted to the engine stand and still being able to remove the oil pan, I have it off and prepared for modifying it for my Jeep project. I am staring at a super clean bottom end with no indications of a failed bearing. The rod play on the crank journals are very small in a linear forward to back motion, no play up and down. There also doesn't appear to be any up and down crank movement in the mains, only a very small amount of linear motion.

My questions are:
-should I replace the main/rod bearings since I have it opened up?
-where is the best place to buy said bearings if I do need them?
-is the mating surface between the engine and the upper oil pan gasketless?
-how can I make sure the tapping sound is from the IP or injectors?
-is there anything else I should do while I have this thing out and partially disassembled?

-should I replace the main/rod bearings since I have it opened up?
Inspect what you find.

-where is the best place to buy said bearings if I do need them?
Try the Mercedes-Benz button at the top of the page.

-is the mating surface between the engine and the upper oil pan gasketless?
I believe so, check with the epc to be sure.
EPC-net Online

-how can I make sure the tapping sound is from the IP or injectors?
Test the injectors, any big rig place should be able to help. You want to find out the pop pressures and spray pattern.

-is there anything else I should do while I have this thing out and partially disassembled?
Visually inspect everything.

In the future, use a number per ?, this will help in folks responding.

MB bearings are HUGE, and they tend to outlast the vehicle, and all it's other parts...

that said, plastigauge them and determine the gap, and see if they pass specs.

the upper pan should be assembled with anaerobic sealant on the mating surfaces.

I second the Plastigage comment.

Anerobic sealant is available from many sources and is the right thing on the upper pan. The lower pan (sump) uses a gasket - I added a THIN coat of RTV (silicone sealant) on either side of that gasket. I haven't run mine yet so I'm not sure if I was successful.

Also, I'd take a hard look at the rear main seal. They are difficult to change on the stand and impossible in chassis (at least, I think so). If it doesn't leak or leaks very little (a little moisture back there is probably OK), leave it alone. But if it needs fixin' this is the time. There is a great thread on the process on here (search for "rear main seal replacement" and it should take you to it) and my build thread ("I'm Back........" - search under my name) has a blow-by-blow of my process which is basically what is detailed in the thread.

Another tip - you need to APPLY vacuum to shut the engine off. As long as you have vacuum you really don't need the engine-mounted pump. The reason to lose the stock pump is that although failure is rare, when they do they distribute little bitty ball bearings all through the bottom end of the engine - small enough to tear up bearings, etc. My S-10 is race-only so I have a VW electric pump. If you need power brakes, etc. you may want the engine-mounted pump for your Jeep.

Good luck.

Dan

Sad, we lost another w116 to a Chrysler product :(

Make that a W126:)