lifter preload w/adjustable rockers

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What he said! I don't know what that is in thousand's of an inch but it's a hydraulic lifter. You need some but not too much. Chevy's always did 1/2-3/4 turn and I bet they had fine thread like Mopar did. If they clatter at 1/2, give them a little more.
I think it's close to .030 or .040"