Abstract: A reciprocating piston machine useful as a pump, a hydraulic motor or an internal combustion engine has a plurality of cylinders in a carrier surrounding a central shaft. The carrier is in turn surrounded by a ported manifold. The carrier and manifold are adapted for relative rotation one to another such that the cylinders periodically open to the ported manifold. Pistons within the cylinders each describe a path in the carrier tangent to a circle in the plane of rotation of the carrier. A gear fixed to the manifold housing about the central shaft induces relative motion between the manifold and the carrier by linkage including gears and shafts and connecting rods of the pistons.In the motor and pump mode, the machine is valveless, and in the engine mode a single valve per cylinder completes the valving functions necessary for an internal combustion engine. A valving cam fixed to the manifold housing biases valving lever arms as relative motion between the manifold housing and the carrier is accomplished.