We use clay and yes it is challenging to measure correctly, sometimes we have to make multiple attempts. Normally we use five balls of clay about .150" diameter to check the intake and three to check the exhaust.PackardV8 wrote: ↑Thu May 03, 2018 1:02 pm In the July 2018 issue of Car Craft, Robert Poole and Mark Magda have a very detailed 3-page feature article on how to check P/V clearance with clay.
Just me, but I gave up on clay in 1964 after being given a lesson by Bobby Allison. I'd read how-to-clay in Hot Rod and wanted to show my expertise. He said, "Clay is for kindergartners. You use it and tell me how much P/V we've got. In fact, do it on three different cylinders. You'll measure three different guesses."
Of course, he was right and he showed me how to do it with checking springs, degree wheel, dial indicator and a clipboard.
So how many of us still use clay?
Or do you use a dial indicator? If so, is TDC valve drop OK or do you degree wheel from 20 BTDC to 20 ATDC?
Or do you trust a computer program to verify P/V clearance?
Once we get an impression, we place a loose valve in the impression and use gauge pins to check the radial clearance.
We always check with the "real" springs, gasket and lash. We consider .070" intake and .090" exhaust to be our minimum with this method. And we like to see .050" radial.
I read an article one time where David Reher described the RM method and it sounded like a better way than clay, just never tried it. Maybe someone can find that and post it here.