Weird Engine Knock - Valve contact?

[deerefanatic]

Yep, that's my next course of action. (Pulling the pan) Only thing is, the entire piston is dark, all black and wet. BUT, there's a visible and able to be felt ridge/crater in the top of the piston.

 

[dieselbeef]

if its hitting the head the ring lads might be flattened? bet its oil not fuel either way