Joe- I have an advantage as I've worked on this junk for 30 years (since I was 12 years old!) and I've been a toolmaker for 24 years and am used to working with clearances and thousands of an inch and stuff. I've built and worked on many race car engines that all needed the valves adjusted nightly. Some weeks we ran 4-5 nights a week and adjusted the valves every night. So this comes as second nature to me. Lots of other stuff doesn't.
Think of solid lifters this way, if you set them to have zero clearance, and the parts expand as they warm up, you could get in a situation where the valve would be held open slightly and would never close. Would maybe even eventually burn the valve. So the clearance gives you some room for the parts to expand and contract and change their relationship to each other without hurting anything. Too loose and they would make an awful racket. The exhaust valves get much hotter and therefore expand more and need slightly more clearance than the intakes. That's why the exhaust valve clearance is always more than the intake valve clearance. And engines that are expected to be run under more of a load and hotter (like a 1-1/2 ton truck or race car) usually call for a little more valve clearance than an engine that won't be worked so hard. (like a car) Cam lobe profile also can determine lash. A smoother profile on a lobe can get by with less clearance than a radical lobe profile that slams the valve open and closed radically. Each new solid lifter cam you buy should come with a tag with specs on it including clearances for the int. and ex.
