Hi I wondered if someone new what would have been the cause of the damage regarding the picture attached. Sparkplug hook bit was missing too! Thanks Maz (no idea about anything)
Pre-ignition, plugs too close to the piston crown, too hot, valve stem failure. Complete engine strip and rebuild, (to fish out the remainder of the piston from inside the engine) new piston/barrel kit, new cylinder head, full gasket set, oil and filter change. Best check the cam chain guides as well for damage while you're in there, and the oil pump
As Steve says. Ran too hot or without enough oil. I'm putting money on it being not enough oil, or really old oil. Could also have been the cam chain or tensioner, but it looks for sure that it's run hot.
I'd go for the cam chain as a first port of call, but you didn't give any pre breakdown symptoms: ie: noises, vibrations, was it smoking etc...
I'd have to dis-agree with the above comment. Not completely though......it is still a part I would check, just not straight away. The reason being, if you look closely at the piston crown, or whats left of it, you can see that it has started to melt before it broke up. This would indicate very hot running plus pre-ignition.
