G'day mate
I eventually had the head taken off. I did look at this suggestion following but was chicken.

You can loosen the injector 1/8th of a turn and crank the engine to blow it out

regards
Paul

Did you ever figure out to remove the precombustion chamber from your Yanmar diesel. I have an YSB12 that needs the head milled and I'd like to remove the chamber before doing this. But, I can't find a word on how this is done (I have the workshop manual!). Did you figure out what the "pin" is for and how to remove it and what it does? Thanks in advance.