PROJECT: How would a Chevrolet dealer build a shop truck in the early 1970s?

[DD1]

Originally Posted by mattfranklin

I should have explained better. Ideally you want the rocker arm to push, on average, in the middle of the top of the valve stem. As the valve seats wear and sink the valve stem gets taller and you’d need a longer pushrod to maintain geometry. If the deck of the block or the mating surface of the head are decked or milled you’d need to compensate with shorter push rods. If the engine is old and lots stuff has been done you have no idea which way to go the cool trick is to use a dry-erase pen on top of the valve stem and color it in. Then you assemble things and rotate the engine through four revolutions or so. Then carefully disassemble and see the wear (or witness) marks of where it was contacting. If the wear mark is in the middle you are perfect. If it’s toward the intake manifold then the pushrods are too short. If the wear mark is closer to the exhaust side then the pushrods are too long. In my case I lucked out and stock length was spot on. There are some good videos on that and I think Comp Cams has a PDF of instructions for that.

Thanks for the detailed explanation. It does help me understand what you did much better.

However this will remain in the category of things I "should not attempt at home," and probably for a good reason. I am happy it worked out perfectly for you; my luck is not usually that good.