Originally Posted by Westlotorn

Another tool used to measure clearance, piston to cyl head and valve to piston is clay.
Clay is moldable and you can mock up the engine with clay thinly spread over the valve pocket or on the dome. Rotate the engine by hand and pull the head and measure the thickness of the clay. This is done on High performance engines where valve pocket clearance is very close or dome to head clearance is very close. Use the gasket you plan to run for the mock up. Clay will compress and mold giving you the information you are searching for. If using flat tops this is not necessary except for valve pockets should you be using a larger cam or larger diameter valves.