I got a knock in my 85 300D from when I plugged the breather and lost oil.
I'm trying to do the Piston connecting rod bearings without removing the engine. To do them I have to remove the huge lower oil pan.
The huge lower oil pan consists of the main large pan and a smaller pan underneath it. By removing the smaller pan and part of the oil pump, you can reach two of the piston bearings but to reach all five, you have to remove the main pan.
The #1 piston bearing was a mess. #2 was okay. The front main bearing was okay.
The larger oil pan--can it be removed? I am asking myself that question now. My biggest concern are the front rubber crank seal and the rear seal.
My question is WILL THE SEALS HAVE AN IMPACT on THIS JOB? Also there may be some interference with the front timing gear.
My theory is that even if you unbolt the lower pan, the engine crossmember will block you, so you will have to undo the mounts and raise the engine.
You may not be able to remove the main pan completely, but you may be able to tip it or rock it to get to the rear 3 pistons. The job will be messy because oil will drip all over your face. If the seals will cooperate I will do it. The engine is basically great, believe it or not.
I wont know for another few days..

The catalog list 52, 51.75, 51.5 mm rod bearings. Assuming crankshaft wear, would you select the smaller size (51.5 mm) bearings?

Save yourself a boatload of grief and pull the engine... You will need to replace the seals, the rear seal will require you to remove the crankshaft.

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Over 21 years I owned several:
w108
w110
w111
w115
w116
w123
w124
w126
w212

If you will tell us who gave you the idea this was possible or legit we will tar and feather them for you.....

plastiguage the bearings after you put them in...just to be certain clearances are in spec....it would ruin your day to find out they weren't after you put it back together and find out the hard way.

I vote on pulling the engins and doing the seals too....if they aren't leaking already they are likely to do so soon....

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

I still think its possible in all due respect.
Anyway I have nothing to lose. If I fail I pull the engine anyway.
I know someone who did it this way on a Lincoln.

The fact that you have to ask which size bearings is an indicator you are not an experienced engine rebuilder... which is different from removing and replacing parts on the rest of the car.....
The size bearings are not determined until you have taken the rods off the crank throw and put the plastigage on them and retorqued them... then you take it off and carefully inspect how much it was crushed comparing it to the ' guage' on the paper container the plasti-guage came in.
Then you order your proper size bearing.
That Lincoln was not a long stroke inline engine. And it was not a diesel.... where tolerances are much closer than most American made gas engines ever considered being...
But it won't hurt for you to try if you are well versed enough to tell when you have hit a procedure which you can not continue from underneath and do well... that is the point at which you change to normal rules...if you are to not lose your efforts from trying it this way...

Do yourself a favor man.!!
Pull it out!
You can do it ....We can help!!
Ask me how I know!

Undersize rod bearings aren't made to take up "slack". They are to be used on a crank that has been turned (machined).

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

If bearing #1 is messed up you are well beyond the cheap fix stage. Find a replacement motor or sell the car and move on....

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Bill Reimels
Now down to one:
1972 300SE 3.5 W109 (Euro delivery)

I just do not see where you will save any effort nor any time by trying to get the lower engine case off with out pulling the engine. It is tough enough to get off with the engine out and on a stand.
The rear seal is just a length of braided stuff that needs to be trimmed to fit in the rear bearing cap and in the block. Problem there is that the lower engine case has to come off and the crankshaft needs to be lifted to get to it. There are two pins that poke into the seal, one is easy, it is in the bearing cap. The other is in the block. Front seal is accessable from the front of the engine.
I think I would look at least look at a new oil pump and chain while I was in there. With what you have I would seriously consider having the crank turned and oversize bearings. Nothing less than a crank polish and a new set of main and rod bearings.

I replaced the rods and mains on a TR-7 in situ once. Even though I had the car over a pit, it was dicey. I would never do that again- at least not in a car that has a crossmember or a 617 with the lower pan and the rope seal. It took me a looong time and I was very concerned about getting dirt in the bearings. My conclusion was that it would have been quicker to pull the engine. I suspect you will agree if you continue

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)

The fact that you have to ask which size bearings is an indicator you are not an experienced engine rebuilder...by leathermang


When I was young I was very competitive and something like this would get me motivated.
I mean all of us are stubborn and tuff or we wouldnt be doing this..but I'm 45 now, at this age we all got other stuff on our minds...
Mr leathermang, you will be 45 someday...

Carrameow, just ignore him. He gets all cranky when his back is bothering him and he cannot go out and mow the grass.

I do have to agree with him regarding pulling the engine. I know that you are a very resourceful fellow and, if I had to bet, I would say that you will get this job done with the engine in the vehicle.

But, I would be very concerned that you will make an error in the process and have to do it all over again. There is significant risk when working upside down in unfamiliar territory.

If I lived near you, I would help you do anything!