From published sources....
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The rocker arm in mechanical valvetrain systems often has clearance issues with the valvespring and retainer and also with the pushrod cup. Most mechanical rocker arms have a relief under the arm near the valve tip for retainer clearance and a relief on the underside of the pushrod arm to clear the cup-end. As the cam lifts get higher, the outside diameter of the valvesprings increases. These issues must be addressed.