An air control valve for directing air flow in a double-acting reciprocable motor, where the valve has a first link which is pivotally connected at one end to the motor and mechanically coupled along its length to a reciprocable motor member; a second link pivotally connected to the same point as the first link, and having an over-center spring detent mechanism to position it in either of two pivot positions; both of the links having alignable transverse slots, with a compression coil spring engaged in both slots; and a slide valve member attached to the second link and pivotally movable therewith, to direct the air flow into either of the double-acting motor drive members, the air valve toggling to its second position near the end of the motor drive stroke to cause the motor to reciprocate in the other direction.