How do I measure valve to valve clearance in an engine?

An easy way to check valve-to-valve clearance with only a dial caliper. You will need to know your Top Dead Center valve lift, which was finished on the cam card you got with your cams. If you don't have that you can easily look it up online. You will need to know what cams you have though.
measure the stem protrusion (the measurement of from the spring seat to the tip of the valve), write it down. Then suptract that from your stem protrusion. This is how much your valve is lifted off the seat at TDC. Then lift the other valve to how much its tDC lift is. The clearance between those 2 valves when both are opn is you clearance.
Typically you want at least .080".