First and formost, don't rotate the crank! This is an interference engine, and the valve will get bent it you do.

Did you drop the chain or wind it out? I'm assuming dropped or took the covers off and removed (somehow I think dropped it, eh?)/

Long pieces of coat hanger wire with a very short hook bent on the end (just a bit past 90 degrees) should fit into the chain to fish it back up. I don't think it will just fall off the crank, but I'm not sure. You may need to remove the tensioner and tensioner rail to see it down there, I've not dropped one on this particular engine (615 diesel I did, though!).

If you can fish it up, weasel it over the cam sproket and wire tie it down and check cam timing as best you can. If completely unsure of cam timing, you would remove the camshaft, set crank (with new chain properly installed!) to TDC on the crank and install the cam at the proper location.

Good luck!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!