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I always set my valves cold and set them .002-.004 tighter than spec for when the motor heats up and the lash increases but to explain to someone that metal expands when it heats up and contracts when it cools seems to contradict what I am doing. Can anyone simplify the explanation so that I can at least sound like I know what I am talking about?
Thanks Mike

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Couldn't say it any simpler,Mike.Hot expands,Cold shrinks(contracts)different metals different rates of expansion and contractions.Iron engine componants expand aprox. .004 at temp,aluminum engines .012/.018 aprox. Most valve setting is for hot,expanded engine componants.If your hot setting is .020 and you set your lash at .016 cold it will be looser at running temperture,closer to your desired .020 setting.The mass (head) is usually a porous metal such as cast iron and grows the most as does your rocker arms,your valves and pushrods are a more dense material,usually stainless steel and chrome moly and is less effected.