The bad:
I tried to get the prechamber out and was not able to make the bike tool method work. The knock is not constant I tried opening each injector line to isolate it as a combustion problem, but the Knock was not effected. If I am going to pull the head I might as well do everything (rings, sleeves, valves, etc). If I am going to do that it might be more cost effective to look for a decent used engine.

The good:
I drove the car and the knock became intermittent and then disappeared after about 5 miles.

I wonder if the chunk has welded itself to the piston or to the head? It has not effected the turbo (yet) which makes me think it is still in there. How soft are the pistons? Are they softer the the cast aluminum that the intake is made out of? Is there a possibility that the chunk disintegrated? I think I will keep driving and if this thing comes back to haunt me I will keep you all posted. Thanks for all your help. Next time I see my proctologist I will ask if I can borrow his endoscope.

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1980 300TD with 1985 300TD Turbo motor and 240D 4 speed.