Maybe you could turn the engine over by hand to see if it has any kind of binding feel to it.

Don't know about your crank pully nut, but the typical size on the 616 / 617 engines is 27mm, the same size as an injector socket.

Ken300D

__________________
--------------------------
1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles