Abstract: A fluid engine for use in pneumatically operated toys such as wheeled vehicles or airplanes. The engine housing has a fluid input cavity which is in continuous fluid communication with a source of compressed air, a fluid delivery cavity which is in continuous communication with a piston cavity bounded by a movable piston mounted in a cylinder member and which is separated from the fluid input cavity by a wall having a valve opening therein, and an open-ended exhaust cavity which is separated from the fluid delivery cavity by a wall having an exhaust opening therein. A valve rod with a tapered end is movably housed in the exhaust cavity to open the valve opening and close the exhaust opening during the piston's power stroke, and to close the valve opening and open the exhaust opening during the piston's exhaust stroke. The valve rod can be operatively connected to the piston to act in synchronism with it either by use of a cam or by use of a network of connecting links.