Valve motion and reversing gear used in oscillating marine engines. The two eccentric rods give an oscillating motion to the slotted link which works the curved slide over the trunnion. Within the slot in the curved slide is a pin attached to the arm of a rock-shaft which gives motion to the valve. The curve of the slot in the slide is an arc of a circle described from, the center of the trunnion, and as it moves with the cylinder it does not interfere with the stroke of the valve. The two eccentrics and link are like those of the link motion used in locomotives.