Just wondering if anyone has done a cheap re-ring and bearing job on an om603. I have not been able to definitively identify the knock on my 87 300D and am looking to have a spare rainy day motor in case something eventually gives way. I've been driving it with the noise for over a year, but thats another story. I was considering purchasing a spare motor with known low compression on the cheap and puting rings in it so I have a spare. The motor comes with a #14 head but I have a spare #17 so the head is no issue. I would of course measure bores and bearing tolerances before spending anything on parts assuming everything is standard ( I know, big assumption but worst case I get some spare parts to clutter up the garage). Has anyone had luck with this sort of half$% rebuild with an OM603. I have built plenty of chevys and fords and obviously the stakes are a little higher and the tolerances are closer, but seems do-able. Any thoughts/experience. Is ~$600 for gaskets, rings & bearings unrealistic?

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1990 300e 230k (old reliable) sold
1987 300D 230K sold
1987 300D 232K 5 speed
1998 E300 140K

Ashley,
I have never known of a planned rebuild being as simple as that. If the motor is low on compression, one should expect stuck rings & so bore damage. The timing chain will probably need replacing as well. Konstan did a well documented rebuild last year on a 617. maybe you should read his threads about it.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Thanks layback. I'll check that thread out. Mostly I was hoping I could get away with a ball hone. The two M103's I've had the heads off of still had factory cross hatching after over 200K miles. Is this normally typical for diesels (OM603's in particular) as well? Are the rings soft or harder than the block liners? Good point about the possibility of stuck rings. I did get away with doing an in car rebuild as described on a ford escort I had years ago and drove it for another 100K, but that was a beater and a spare motor could be had for $100 at the wrecking yard, so nothing to lose. Might still be tempted to buy the extra motor just for parts.

__________________
1990 300e 230k (old reliable) sold
1987 300D 230K sold
1987 300D 232K 5 speed
1998 E300 140K

Just to clarify my last post, obviously not suggesting an in car rebuild on the benz (I wish). But was able to pull it off on the ford.

__________________
1990 300e 230k (old reliable) sold
1987 300D 230K sold
1987 300D 232K 5 speed
1998 E300 140K

Babymog has had several apart and has reported that the cross hatch has been there. You might want to contact him for specific questions. He knows his way around 603's.

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D

Cheaper and easier to find a bad car with a really good 603 engine in it. With a little luck peddling off the excess just might give you a free engine except your labour to remove it.

A 603 engine worn to the point of needing a rebuild may not turn out that cheap if you find the internal wear bad when you take it apart. Any money paid for it up to that point may be considered wasted.

Should be lots of engines with bad heads out there that the lower block is sound still. This may be one case of when the heads crack on other peoples cars it works in your favour.

Parting a car out at my house would get me in some trouble with the city and probably the wife unfortunatly (not that I haven't thought about it anyway). I was hoping to find a good engine w/cracked head as suggested but just haven't found a good one yet. Any leads would be appreciated. I suppose I should put up a wanted add on here.

__________________
1990 300e 230k (old reliable) sold
1987 300D 230K sold
1987 300D 232K 5 speed
1998 E300 140K

The best running Chevy in the marina is the one that we slapped together with cheap parts and no machine shop work. I have had several expensive rebuilds go south quickly. It doesn't seem to make sense but I am saying from personal experience that quicky rebuilds have been very successful assuming the engine was running and within spec. I wouldn't expect them to go as many miles as a new engine.

Patience and some effort are usually rewarded.

So I'm probably insane for this but I found an engine dirt cheap with all accesories etc. It's a 603.970, but it's the factory rebuild with the aluminum tag near the bell housing. It's been torn down by the previous owner who found it at the junkyard but everything appears to be clean. Bores look good and pistons look clean. I figure worst case I can sell stuff from it if it measures out of spec. I will of course measure everything before buying any parts (those rings are expensive). Anyone know if my 3.0 injector pump and cam will be a direct fit? Any other possible issues with puting this in a 87 300d?
Thanks,
Ashley

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1990 300e 230k (old reliable) sold
1987 300D 230K sold
1987 300D 232K 5 speed
1998 E300 140K

Some one please correct me if I am wrong but isnt the 970 the 3.5 "rod bender" ?
Ashley,
do a search on it.
Its your motor stroked. Unless you are both brave & a little fool hardy, best let that one pass even though it may have the upgraded rods.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Yup, .970 is a 3.5. But the short block is a bolt-on replacement for a 3.0.

I don't know how good you are at inspecting engine internals. This will give you an idea of what to look for as an indication of bent rods in a 3.5 -





Here's one way to identify upgraded rods -



Sixto
87 300D

An OM603 with known low compression may need more than just rings and bearings. OM603s are known for being very expensive engines to have rebuilt. If you have your own machine shop you may be OK but if you have to pay someone else to do the work you'd be better off with a good used engine.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I know these are known as rodbenders but I can't find any evidence here or elswhere of the new design rods failing. Looking at the pics that I beam (Thanks Sixto) can probably support double the moment of the original. Forgot to mention, this isn't the original motor I was looking at with low compression. It came out of a flooded car at the wrecking yard which amazingly didn't get water in the motor. I'm planning on measuring and inspecting everything. Pistons don't appear to have any wear. Worst case it might need liners pressed in and bored (doesn't look like it though). I'll post some pics once I get some time to take everything out of boxes and measure.

__________________
1990 300e 230k (old reliable) sold
1987 300D 230K sold
1987 300D 232K 5 speed
1998 E300 140K

You cannot put liners in the 3.5 block I believe. Mercedes did not leave enough material to enable even original liners to be installed at the factory. If you can find a comparison photo of the top of a 3 litre block and a three point 5 litre block you can see how little material is left between the bores.

To me it is an insane small amount for a diesel engine. At one time in my youth I could visually squeeeze a model A ford block bores with my bare hands when the head was off. Take the same senario with a high compression diesel and expect it to live happily ever after was insane.

Stronger rods to support and help retain the structually weak bores was not really the answer. It was too late other than to discontinue the 3.5 program or design another block. No doubt the stronger rods sufficed on some but this may have been just good fortune.

The second issue is thrust loading on the pistons as the wrist pin is much further down on the piston. Overall that 3.5 block is not a good design. The thrust loading was designed to be dealt with primarily by the skirts of the pistons. In this design too much side thrust is left to the upper portion of the piston to deal with. Overall just an inferior design.

The advantage of finding the watered engine cheap is the newer head that should be preserved. Keep the injector pump lines etc as well as they are specific to the later head. Now if you could find a good three litre block and install the newer head you would have quite an engine.

Use the old remains of the 3.5 as a boat anchor. They are absolutly trouble free for that application. You stated that you could find no cases of the replacement rods failing to correct the problem. There are many of them as they do not really address the real problem. I do admit they seemed to help in many cases. Failure still was far from unknown with them over time. The manufactures motavation was basically just to get these engines past the warranty period. Today might have brought a class action suit.