I have seen the key shear, I have seen the crank break right there as well. I know it sounds wierd, but I have seen it.
Yes, you will have to pull the head since the valves are most likely bent, then the harmonic balancer to check the condition of the lower gear. Then line up the TDC with the cam then install the injection pump. You will then have to set the timing on the pump manually.
After thinking about this for a while, I would make sure the engine is putting out proper oil pressure. I have seen the camshaft sieze up in the stand and cause the chain to jump, then when cooled down, it will turn OK.
Check EVERY THING!!
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