71 Dart 410 stroker ..
Remember most piston to valve clearance recommendations want more clearance on the exhaust valve because it will usually get closer than the intake. I see that Tony reported his numbers when he degrees the cam. He then advanced it 2 degrees which again will affect the piston to valve clearance. I know that Tony has said he does not see any marks in the other 7 cylinders but let's look closely at Tony's picture of the beat up piston that I have posted. To my eyes
I see a perfect half moon arc on that piston. To me it looks like before that valve was destroyed it clipped the piston forming that arc.
If it keeps hitting it, it will break a chunk right off the valve. That hardened piece of broken valve becomes trapped in the cylinder and beats up the aluminum (soft) head and piston while it bangs around inside the cylinder.
That one cylinder may have had a slightly weaker valve spring.
The engine may have slightly over revved and floated that particular valve.
But imho that arc that I think I see on the piston is a telling sign.
I am not an engine machinist but imho the piston hit that exhaust valve.
Remember most piston to valve clearance recommendations want more clearance on the exhaust valve because it will usually get closer than the intake. I see that Tony reported his numbers when he degrees the cam. He then advanced it 2 degrees which again will affect the piston to valve clearance. I know that Tony has said he does not see any marks in the other 7 cylinders but let's look closely at Tony's picture of the beat up piston that I have posted. To my eyes
I see a perfect half moon arc on that piston. To me it looks like before that valve was destroyed it clipped the piston forming that arc.
If it keeps hitting it, it will break a chunk right off the valve. That hardened piece of broken valve becomes trapped in the cylinder and beats up the aluminum (soft) head and piston while it bangs around inside the cylinder.
That one cylinder may have had a slightly weaker valve spring.
The engine may have slightly over revved and floated that particular valve.
But imho that arc that I think I see on the piston is a telling sign.