i need help w/duster engine

I still don't get this ,if the valve is open all the way then how could it be open anymore regardless of where the piston is,your clearance is your clearance the cam and crank will come to a point where both will be at max stroke/lift in relation to each other,but not necessarily at the same time just because you have .508 lift doesn't mean you have it at TDC if the valve is opening then the piston is moving the valve only hangs open for a few degrees of crank this is why it gets checked.I still say that if you bring your assembly around to max.lift then check how much you can drop or push the valve into the cyl.that is your clearance at max.lift only,now with the dial on the stem rotate the crank +/- degrees you will know how much room you actually have.