05 polaris predator engine knock

Newbie here..My first polaris predator 05, bought used supposely only around
60-70 hrs, word of mouth.
Ran good for a month of weekends only around 4hrs. operating.
Had small ticking sound, that bothered me, forums help and adjusted the idle higher..Fixed.
But...the other day I went to start, very hard to start. When started had a
bad knock.Not a tick like previously noted.
Valves were out of spec on intake = .001 & .0015, exhaust good.
Bought shim kit and fixed clearances. Placed timing back. Put back together.
Still knocks.
Tore back apart. Pulled top end found piston pitted bad with alum. shavings.
Valve side of top end also pitted up.
Valves no sign of contact.
Cylinder wall has no scoring on it, nice and smooth.
Crank arm has no play. thought possible bearing might of moved.
No metal in lower crank oil either.
Please help. I'm just starring at it at a loss..