Rev-
I think you meant the pistons become close to valves, not the heads. Piston/head clearance should always remain the same, even with worn crank bearings, which would allow very VERY minimal deviance in the stroke of the cylinder.
And, to my undersatnding, "piston slap" is the result of badly worn rings, in which you can hear slight rattling of the pistons in the cyclinders due to rings that are wayyy out of spec, and excessive blowby exists.
8) Fashionably late on this post!
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Mud, sweat, and gears
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