Thanks all for your comments.
A mechanic friend of mine suggested that the offending item may be impaled in the piston crown and contacting the head at each TDC. I will ask around to see if someone has a borescope.
The engine idles and runs smoothly, but seems to have lower power than before.

ALCOHOL MISTING.
I had the alcohol misting installed in a Mazda 2.0 litre Diesel car, with excellent results, giving a 10-20% power boost at WOT. This system consisted of a 12v water pump (washer pump) with a microswitch on the IP to close when the pedal hit the metal, turning the pump on and misting denatured alcohol into the inlet manifold. As the injection only happened at full power, the alcohol usage was minimal, but it gave an improvement in diesel economy due to greater power and shorter acceleration times.

I installed this in an effort to improve the OM617, non-turbo, power output.

__________________
Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.