Some of what Hotrod is telling you in his own way:
http://www.camcoindex.com/svcman/moonbook.pdfFor those who want, some of the stuff a cam does(not a complete list) are as follows: Lift(just one thing), Accelerate(just one more thing), Degree timing( another thing),Decelerate(another thing), and it matters if you have a flat follower(tappet) or a roller follower. The intake valve is cooled by the air-fuel mixture(smaller "lash") The exhaust valve is heated by the outgoing charge(larger "lash") With funky wear on valve stems, rocker arms, and pushrods, not to mention the lifter(tappet), and cam. You can see why there is a "recommended" clearance between the rocker arm and the valve stem. Add hydraulic lifters and let the fun begin. For most of us, set to the book seems like a good idea.
