... It rides on the camshaft. When the cam lobes push it upwards, it opens the valve;♣ The engine ... oil forces the piston upward until it contacts the push rod. When the cam raises the valve lifter, the ... placed on the inner piston which tries to push the oil back through the little opening;♣ When ... down, the lifter is pushed down by the push rod. It adjusts automatically to remove clearances. Auto Hydraulic ...