Abstract: Internal combustion engine valve rocker arms adaptable for changing the horsepower output of an equipped engine, which rocker arms may be alternately set to prevent operation of the valves of cylinders that are to be selectively deactivated. Each rocker arm is formed of two radial members pivotally mounted to a common shaft that are joined together by a slidable key which may be shifted to a position in which the two radial members are disengaged from each other so that the first radial member reciprocated by the camshaft push rod does not transmit motion to the second radial member bearing on the valve lever. A latch device retains the second radial member of a conventional valve rocker arm in the open valve position, when the radial members are disengaged from each other.