THis is what happens when a valve REALLY smacks a piston  The cause of this was a seized valve guide in
a 1978 Euro motor.  The engine was sold fore a core with parts to repair it (head, spray bar).  The piston was OK.
 

Smmmmack!  Yeah....not good.

Head was destroyed as well...

Junk.

I shoudl have taken some more pictures.  The rocker had broken and taken out the spray bar.  The cause
of this appears to have been a seized valve guide.