There's some faulty logic going on here. First of all the top of the piston has nothing to do with piston to valve clearance. If you look at most pistons they have valve relief pockets. It's the depth of the pocket that you need to be concerned with. A domed piston could have more valve clearance than a stock flat top.
Next is the faulty assumption that maximum valve lift is the variable that causes insufficient Piston to valve clearance.
The point where the valve comes closest to the piston is
not TDC or maximum valve lift. The valve is not fully opened when the piston is closest.
It's closest during overlap about 7-14 degrees ATDC for the Intake and 7-14 degrees BTDC on Exhaust. Usually the Intake valve is the problem because it's bigger, but never assume.
It's a good idea to check valve to piston clearance with clay before you bar the engine over. You don't need the cam to do this. You can mock it up with one piston and rod, and old gasket of the right compressed thickness and a dial indicator. Use a light checking spring to make it easy.
If your valve clears the pocket by .100" at TDC and maximum lift it's ok. If not you need to do further checking with the degree wheel.
Don't ever assume you have adequate valve to piston clearance!
I have a stock lift rule cam that interferes with a stock piston because of a tight LSA and a minimum quench dimension.
Read more:
Crane Cams FAQ
Isky VOTC
