[QUOTE=MikeTangas]I guess I'll have to drag it down here and pull the front cover. Any ideas on a cause, or likely candidates to checkout?

QUOTE]
I'd guess that something else broke and that's why the chain snapped. It would take some inertia to snap a chain like that, cranking without engine damage wont snap a chain.. This may explain why the dude had and extra engine in the first place!....

These OM's are not like your M117, no front cover, just nasty pita countersunk pins which hold the rails in place.

I'd Drop the pan first and see what's in it.....

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Over 21 years I owned several:
w108
w110
w111
w115
w116
w123
w124
w126
w212