The cam lobe of the camshaft is placed directly above the bucket tappet, such that the lobe comes around it and pushes down the bucket tappet and the valve, thus opening the valve. In an overhead
camshaft with rocker arm, the cam lobe comes under the valve lifter, and causes the rocker arm to rock or turn the lobe and pushes down the valve steam and it moves down to open. When the cam lobe passes the valve lifter the valve spring retains back to the original