Mike,

Sorry it has taken so long to respond...I couldn't remember exactly where the chain tensioner rail broke, so I had to go dig it out of a box in my shop this morning. It broke at the pivot point and was kind of just laying in the chain cavity on top of the pivot pin. The tension piston wasn't contacting the rail any longer.

What really caught my eye was the picture and symptoms you have are identical to mine. The chain was wrapped half way around the valve sprocket and broken, and the starter would not turn the engine (engine locked). I think this type of failure could happen with a bad tensioner, also, but I think the chain break and the engine lock are undoubtedly linked. I can't think of any other reason your engine would lock, and even if it did lock, this wouldn't put a lot of force on the chain. I suppose the chain could have broken and then got wrapped around the bottom sprocket, but I have heard many mechanics say that chain breaks usually occur when something else fails first (ie. rails, tensioner, etc.).

Anyway....hope you can get to bottom of the trouble and fix it with a minimal amount of hassle. If it is like my situation, a new chain, sprocket, repairing the oil pan, renting a hoist, and tensioner rail only cost me about $400, and I did the labor with a lot of help from this forum. If your oil pan is okay, you may be able turn the crank backwards to free the chain, fish it out and pull in a new one without pulling the engine.

Good luck!

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