I too, have now lost the timing chain. At this point, it is only a noise, but must be investigated and corrected.

It has also been brought to my attention that the center gear on the timing chains appears to be cast iron. I would have expected "machined steel" or "investment cast steel".

A 500SL is in the shop beside my 500E with the same problem. In his case, he noticed low oil pressure in the upper RPM range. It turns out a rail broke and was clogging the "oil pick up?"

As I determine more, I will post results.

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dwight