Do you know any history of this bike? An EX500 would have to be pretty lean to do that, and it would be running hot.
EX's are famous for over heating and warping the bejesus out of the head
What does the head gasket look like? (You can re-use the head gasket if it's still flat. Clean it up and put a thin coat of your favourite spray paint on it and you're good to go).
When you're putting it back together be SURE to lap the head and cylinder surfaces AND measure the cylinder for taper
It's been a while but I thought EX's had ART pistons and 1mm rings... which those pictures aren't.
EX's are famous for over heating and warping the bejesus out of the head
What does the head gasket look like? (You can re-use the head gasket if it's still flat. Clean it up and put a thin coat of your favourite spray paint on it and you're good to go).
When you're putting it back together be SURE to lap the head and cylinder surfaces AND measure the cylinder for taper
It's been a while but I thought EX's had ART pistons and 1mm rings... which those pictures aren't.