Abstract: A cylinder deactivation device includes a stud rigidly engaged with the head of an internal combustion engine, a rocker arm, a rocker ball, a stand element attached to the upper end of the stud, a cylindrical sleeve having an interior ridge in the inner wall thereof, and a compression spring for exerting a constant force urging the rocker ball against the rocker arm. The stand element has a longitudinal hole and a plurality of transverse holes which extend to the longitudinal hole and a plurality of steel balls which move outward in the respective transverse holes in response to insertion of a tapered plunger into the longitudinal hole to engage the internal ridge and prevent upward movement of the sleeve. The rocker ball engages the bottom of the sleeve, and acts as a fulcrum for the rocker arm when the tapered plunger is fully inserted. When the plunger is retracted, the steel balls recede and do not engage the interior ridge, allowing the rocker ball and the sleeve to yield to the rocker arm.