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back to front Ron. you’re right about opening times but that’s just a side effect. Opening and closing times are usually stated at a given valve lift (eg 1mm) to take clearances out of the equation, since you should be measuring on a stone cold engine. 0.2mm is the minimum clearance and 0.3mm the maximum... just as it sounds. Once warm (bloody hot) the parts have expanded and lost around 0.2mm of clearance, so it’s ideal at zero, the engine can live with 0.1mm of free play without too much of a hit. What you really don’t want is less than the minimum 0.2mm, as this means once warmed up the valve will never fully seat when ‘off cam’ losing compression and adversely affecting performance.
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