spark plug damaged

make sure that is the right length plug. make sure the timing is not too advanced, (engine will kick back if it is). your gonna need at least one valve open or the vac. wont suck anything up ( no air movement in cyl.) Might try removing the ex. pipe and opening the ex. vavle and blow air into the plug hole to get the pieces out, or suck through the pluck hole whit one valve open. If the piston isnt broken off the connecting rod, there is a 99% chance the piston is ok. Pistons are tough. The pieces should come out without too much trouble. BOOM!
:ohmy:

and if the motor has good compression in that cyl.?