You are dealing with a motor with timing belts -- a main one for the crankshaft to camshaft connection, and, I believe (memory worries me on this, I must admit) also a small one from the rear of the camshaft to the diesel injection pump. Could it be that the latter is broken? If the former were broken you would know it by now on a diesel because of all the banging sounds as parts which shouldn't touch destroyed one another by contact.