A year or so ago I had a timing chain tensioner rail fail and the timing chain locked up the engine. Your original post alluded to messing with the tensioner. When the tensioner or rail fails the chain has way to much slack and can actually wrap itself around the bottom sprocket. There is not sufficient clearance between the upper oil pan and the sprocket for more than one layer of chain, and so the engine stops. If you turn the engine backwards slightly, it will release the engine and function properly once more, including running. I locked mine up twice before the chain finally broke.

Your problem may be something else entirely, but sounds eerily similar to my problem.

Good luck.

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold