Abstract: The motion converting device includes a double-threaded power shaft having two right-hand channels, two left-hand channels, and which is driven by a piston connected thereto. A power gear positioned in the path of movement of the rod has a central bore through which the shaft is received. The power gear is mounted in a guide block which holds the gear against movement axially of the shaft and which permits the gear to rotate. The guide block also has a bore through which the shaft extends. A spline connection operatively connects the shaft to the gear and permits the shaft to move axially of the power gear. First and second directional sleeves are mounted in the guide block at positions spaced axially from the power gear and are adapted to receive the rod therethrough. Each of the directional sleeves has at least one cam therein adapted to engage in one of the channels. The guide block holds the sleeves against axial movement while permitting them to rotate.