These things are always a bit of a gamble, bit failing the vac method i would pour a very small quant of engine oil (not enough to hydro-lock the piston) but sufficient to cover piston cap, this way the piece should stick through a few combustion strokes allowing it to be burnt or crushed - the gap between piston and head is tiny, less than the plastic, that said you don't want it to wedge one of the valves open.

It's a risk, but work through the easy options first.

Good luck

__________________
David


1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)