Ignoring the slow-rate acceleration and deceleration ramps that are built into the cam by altering the lash specification causes the opening and closing of the valves to become a violent, destructive action. If the clearance is specified as .007", for instance, there is an area of the cam lobe .007" tall where the transition is made from the base circle to the beginning of lifting the valve that is very slow until the clearance is taken up and all the parts are solidly in contact with each other- - - -then the rate of lift increases dramatically. Ditto for the lobe shape just before the valve face touches the seat on closing- - - -the rate of speed slows down.
Increasing the lash adjustment results in the rocker arm hammering the valve stem at a high rate of speed on opening, and the valve slamming down on the seat at closing. Anyone who has studied even rudimentary camshaft design should be able to understand those principles. Every 9th. grade high school kid who ever attended one of my engine principles classes left with an understanding of basic camshaft design!
Carl, the increased lash for heavy duty use is to account for valve stem growth during high speed, high load full-throttle operation due to increased valve temperature.
Jerry
