Last year my mechanic was working on a 420sel with a jumped timing chain. He re-did the valves, guides etc and after putting the engine together and firing it up, he heard a ticking sound. He was trying to determine the nature of the ticking - when Bang - there was a loud noise and the engine was freewheeling. Upon disassembly, the new chain was broken in two places 4" apart similar to the pix above. AFTER ONLY 3 MINUTES OF RUNNING!! It was an after market chain. He rebuilt the engine again with a mercedes chain and the car is still running great. Don't know if it is co-incidence or if these after market chains are poorly constucted. My mechanic thought something had jammed in the engine but could not find a possible cause. Because the new chain has been working for over a year now - he was pretty sure it was the after market chain that was just defective. As an aside - when the after market chain broke #7 piston got damaged (don't remember how) and scored the cylinder wall resulting in the block being sent out to get a new sleeve installed.