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I think I understand what you mean. Your thinking that when the motor heats up, the pushrods expands, and this would make the adjustment tighter correct? Well..everything expands and grows not just the pushrods, the rocker arms, the heads, the pistons, the bores, the rings..everything. The heat excites the molecules causeing them to move. Just like airing up a tire..You add molucules they bump into each other, they have now where to go, they expand the tire..It heats the tire up also....

When pressure goes up so does temp they are proportional. As pressure goes down so does temp. This is why those old Deodorant cans get real could when you use them for a few seconds. This is actually the basic principle of how a A/C unit works.

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No Bob,the pushrods and valves are a denser(tighter grained)material and are less effected by heat.Combustion tempertures have the greatest effect on a pourous cast material such as the head,combustion tempertures are transferred through out the mass casting causing the growth, conversly the rockers,iron or aluminum conduct the heat from the head mass also,but to a lesser degree than the head mass.Valves are the lest effected since they(exhaust) are designed and made of material that would only be effected by extreme heat that you will not see in an engine.The main growth to be concerned with here are blocks and heads or "mass,pourous metals"