I had to swap out a sump case on a 617 engine. That alone would deter a crankshaft swap, never mind that MB bottom ends are notorious for longevity and being bomb-proof. I wouldn't disassemble one of these engines unless it was absolutely demanded.

My tech is skeptical about doing anything non-stock. He is warming up to the 4-sp. If I told him I wanted to swap out the crank, he'd fire me as a customer!

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Peter
1985 300TD 4-speed 212K
1992 400E 343K
2001 E320 72K