How do you check piston-to-valve clearance?

The targets (Speedway): at least 0.080 in on the intake valve and 0.100 in on the exhaust (the exhaust runs hotter and expands more). Don't go below these, especially for high rpm.

The clay method, in outline:

1. Make sure everything is in good shape first — no sloppy timing chain, worn guides, loose rockers or bent pushrods — or the reading is off.
2. Install the cam at the timing you'll run, with solid checking lifters (or lifters that won't collapse) on the cylinder you're testing.
3. Spread clay (Speedway uses Play-Doh) on the piston top, install the head with its gasket and light checking springs, and torque it.
4. Set the rockers, rotate the engine by hand through the valve events, then pull the head and measure the thinnest point in the clay over each valve pocket.

A degree wheel, piston stop and dial indicator give a more precise check. Speedway's article covers that method too.