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Member Poll
How many miles on your W124?

0mi - 50,000mi
0mi - 50,000mi
5% [87 Votes]

50,000mi - 100,000mi
50,000mi - 100,000mi
10% [183 Votes]

100,000mi - 150,000mi
100,000mi - 150,000mi
21% [382 Votes]

150,000mi - 200,000mi
150,000mi - 200,000mi
25% [448 Votes]

200,000mi - 250,000mi
200,000mi - 250,000mi
18% [334 Votes]

250,000mi - 300,000mi
250,000mi - 300,000mi
10% [181 Votes]

300,000mi - 350,000mi
300,000mi - 350,000mi
5% [86 Votes]

350,000mi +
350,000mi +
7% [119 Votes]

Votes: 1820
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Started: 03/14/2011

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» W124-Zone.com » Technical Issues
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603 Crank blueing/discolouration ? ? ?
Hello to all. I'm currently rebuilding a 3 litre turbo OM603 and have a few questions that I hope some one may be able to answer. There will probably be more later on. :-)
I've stripped a few engines in the past but I've never come across this before.

Basically, what has caused the blueing/discolouration that can be seen on the crank ?

I suspect it is the result of some previous machining work done to the crank ? It doesn't appear to have been caused by any type engine failure as the rod bearings appear fine. They have wear but normal wear.



Next question is in regard of con rod movement/free play. The following pic shows a con rod at the left of pic. pointing up, minus piston fitted to the crank.
Now first off there is a lot of side to side (lateral) play of the con rod on the crank pin. Probably around 1.50 mm maybe 2.0 mm side to side. Seems a lot but I guess that's the way Mercedes build them.
The thing I don't get is if I hold firm the con rod on it's crank pin and then grab hold of the small end / little end / wrist pin / piston pin (whatever you call it ) and then rock side to side, I have a total of about 2.0 mm of movement. The rod is rocking on the crank pin. As I said the rod bearings have wear but they don't seem to show sufficient wear to cause this.
I'm waiting on some new rod bearings to arrive which may well answer my own question but thought I would post the question anyway in the mean time.


I have measured the crank pin with a micrometer and it appears to be within spec. Every rod is the same. Looking at the amount of free play you would think this engine wouldn't make any oil pressure at all.
By the way I have no history with this engine.
Any help would be appreciated. Thanks.
Mystery solved. It seems the blueing is a result of an Induction Hardening process. :-)
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