I've just started rebuilding an OM603 turbo motor, all is going well but I have never seen anything like this before.


Are these heat marks caused by a previous machining job on the crank ?


I have no history with this engine but it doesn't seem to be in too bad a condition. Rod bearings were worn but not too badly. From the info I have, the crank pins are within spec.


The rods do have a lot of movement on the crank. Is this a Mercedes thing ?


Thanks.

maybe the crank was machined, and that is journal heat treating?

the pic is hard to tell, but are any main or rod caps discolored?

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Run short of oil? Some sort of straightening process? You'll want to have that shaft checked for straightness.

That’s from the original induction hardening of the journals. Tge crank in my 2005 CDI looks the same.

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That’s from the original induction hardening of the journals. The crank in my 2005 CDI looks the same

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The blue color is evenly dispersed and spot specific vs randomly located throughout the crank, IMO it is part of the manufacturing process. If it had been hot enough to cause the coloration while running the engine would have seized.

Measure it and if all is in spec with smooth bearing surfaces...ride on!!!

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Thanks for the replies. The heat marks must be as a result of some sort of heat treatment when the crank was manufactured or from a recent repair. They are so even and regular. When I first saw the blueing I thought, "wow, every rod bearing has spun!" but then thought, no that can't be right.


Everything does measure up fine. Thanks again.
A pic of the rod bearings.

Even the con rod bearing cap is blue in 2nd picture r/h side .Could be problems before like a lack of oil damaged the bearings then it was rebuilt and re shelled. I dont know for sure .

If it was lack of oil, the whole crank would be damaged and discolored. If it didn't make bad noises before, don't sweat it and put it back together if it all measures within spec

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100 % percent that is induction hardening. The far right rod cap in pic 2 looks blue but I'd say that is a reflection pending a better pic / pulling the rod cap.

As for the rods being loose, from what I recall, these engines use piston guided rods rather than crankshaft guided rods.

I'd be more concerned about the rod sticking out of the oil pan area. . . . tee hee..

I'd be interested to see how your engine is mounted on your stand? How do your cylinder walls look.

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Generally a simular thought to mine. If it got that hot as the rod caps seem to indicate. Chances are pretty good that the softer coatings on the bearings were totaled by that much heat. Indicating it was repaired probably at one time. I will go out on a limb and suggest the rod side clearances are or should be found out and checked. To see if they are over. These are just my thoughts not backed up by a lot of experience.


I thought when you mentioned the rods seem loose you were relating to their side clearances. If you meant bearing play is another story. All I really am pretty sure of is there exists. Indications of real overheating at one time.


The bottom ends of these engines can usually go the reasonable life of the engine with the bearings still decent. So if it is assumed they were replaced once already. Why are they bad again. Or did the overheating occur with the bearing set still present?


You cannot come to any other conclusion that there was excess heat at one time with those rod caps discolored appearances. Between the failure of the oil cooler hoses and people that damaged their oil pans. Or never checked their oil level. Or had an oil pump failure. Possibilities do exist.

x2, induction hardening usually leaves a very subtle bluing on the crankshaft, while this coloring seems far more pronounced. Also the fact that the rod caps show the same bluing. I've never heard of induction hardening of rod caps. Crank yes, rod caps no.

IMO this engine was run without oil, which caused this heat discoloration.

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I'd check out Google images using the search term "OM603 crankshaft". You'll turn up tons of images of cranks that look exactly like the one shown.

This and the fact that there aren't any other symptoms of bearing failure seems to suggest that the coloration came from a manufacturing process.

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I am unsure but have to almost conclude. The responses so far at least. Are partially based on how well your pictures are displaying on members monitors. The reproduction I get is pretty clear that real heat was involved on the rod caps. Also on my monitor the main bearing caps look normal.

The computer I am using is average in my mind. As is the monitor. I have questions about me as an observer but that would be subject to another thread. Perhaps different service providers. Have different qualities of transmission. Individuals color perception also may enter into the picture as well. I use the American spelling of colour to not confuse Americans.

I am interested in what the crank journals are like. I do know that I would be checking the connecting rods for concentric big ends. At least that is a relatively inexpensive issue if it needs addressing.

I would also plasti gauge the rod bearings now. I assume the plasti gauge product is the same. Yet perhaps sold under another name in England. Whatever bearing clearance is present and what the surface of those bearings and journals look like. Can tell a lot in my opinion.

If for example the rods bearings where replaced everything might still be excellent. If the bearing clearances are normal and all appear well. visually. I would not replace them. Checking the main bearings in a similar manner of course.

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