What exactly is different about the engine? Is it just longer stroke? or is the bore larger as well?

And what about that flexible hose in the exhaust manifold of all OM603 engines. That looks like and expansion joint to me. The block and the manifold should have nearly identical thermal expansion. But the head's expansion rate is probably about 10 times larger than the iron parts. So maybe we get all of the issues with the heads squirming around on the blocks in addition to the bonus of longer, possibly more heavily loaded rods.

If MB knows what is going on with these engines it would help if they would tell us now. There could well be ways to adjust the excessive stresses out by de-tuning(via fuel timing), rpm limiting, or something.

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JMF