The shop manual for my 1988 Toyota pickup with the 22-R engine says to measure the valve clearance when the engine is at operating temperature.
By the time I get the valve cover off, and get ready to start adjusting, I've no doubt that the engine is no longer at operating temperature, or anywhere near it.
Since the head is some alloy of aluminum, I would think that it *would* be important to measure at some known temperature, or some other temperature where the values for the gap have been appropriately modified.
Basically, it seems to me that the aluminum head is around
4" thick, so calculating the diffence in the coefficient of thermal expansion between aluminum and steel should allow one to get the adjustment adequately close.
Am I right?