71 Dart 410 stroker ..
Not really.
Ive just got done reading the entire thread and when i looked at the pictures i saw thee exact same indicators duane describes. That one made contact BEFORE it broke into pieces. Thoughts are not enough spring pressure and to end i would factor the cam being advanced expoilted that.
If the cam is what i think it is, 155-160 seat is where they would be happy.
My advice to all is change the springs everytime you change the valves.
Happy drag racing
I could be wrong on what I think caused the failure. It could have broke the valve stem.
It is possible that Tony checked the valve to piston clearance and just did not post that he did.
I know that lots of builders like to run 11/32 diameter valves because they are a bit lighter, and help air flow a bit.
I stay with 3/8 because more bullit proof.
But I am trying to emphasize to eliminate guess work and speculation when building the motor. Those recommended piston to valve clearance are recommended for a reason.
Connecting rods stretch at high rpm getting closer to the valves and heads. Valve springs can float if springs get weak and the lifters are not accurately following the cam profile. Timing chains stretch and always have some slop to them. These things will use up some of that clearance, but if you have enough you avoid catastrophe. If you were marginal to begin with and the clearance is not enough, the result is expensive.
I have had a cam with .585 lift that would not clear the Pistons adequately. Had to get valve reliefs deepened at machine shop.
My current build has over .707 lift and with cam at 108 centreline
Has .135 clearance on both valves without modification to Pistons.
Hats off to Ross racing Pistons for getting it right.
That's how much difference there can be in the grind of different cam lobe profiles. You have to check piston to valve clearance at the same time you are degreeing the cam because the two are interrelated to one another. IMHO. But occasionally parts can just break.
But in this case I think the clearance was not enough because of the mark in the piston valve relief.
