The piston didn't look as bad as I expected. How do the cylinder walls look?

 

they look fine, the valve actually stayed in the guide in the head, it just went up and down hitting the piston..

 

Sounds, and looks like a faulty valve, but I wouldn't totally rule out the fact valve float could have caused it to fracture. The valve doesn't have to hit the piston to be designed by valve float. Running too week of spring with a cam more aggressive than the spring was designed for will allow the valve to bounce on the seat. That action simulates an air chizzle on the valve.

 

Looks like it could have been a lot worse. The short block is probably ok.

 

That makes sense, but on the other side of the coin, a real stiff spring that slams the valve against the seat can't be good either...

 

Well actually, the cam lobe sets the valve on the seat. Too weak of a spring that can't keep up with the lobe will float(stay open), and when the spring catches up there is no sloping lobe to set it back on the seat, it slams on the seat and causes breakage.

 

I stand corrected

 

also just cause a spring is rated at a certian lift doesnt mean its the right seat pressure for that application