Hatterasguy says: "They need the timing chain and rails done every 100k like clock work. Don't try and put this off on a M116 or you will be looking for a new engine."

I've read a few hundred posts re timing chains, and I am under the impression that the 420 has an M117 engine. This timing chain issue reminds me of the many "oil change" threads; not much agreement to be found.

Does the M117 engine have the double chain? Is it the chain, the rails, or the tensioner that should be the more-closely monitored? Obviously, if I'm to go with the aforementioned vehicle, I'll go through all the records, and just as obviously, will not want to take any chances for a TC failure, but don't want to spend unnecessary money, either.

One thread I read through suggested to line up TDC on #1 cylinder, and check to see if the cam tower mark lines up with the mark on the gear as a way to check stretch. Theory being that no stretch meant no problem with the TC. Later in the same thread, it was suggested these double-row (if that is what the M117 has) are virtually bulletproof from the factory, and that the tensioners were all that needed to be replaced at the 100k interval.

Where is Larry Bible when I need him?

Thanks for all the commentary, and please keep it coming.

While I'm at it, what kind of fuel consumption am I to expect on the 420SEL?

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1980 300SD 146K miles.