Abstract: A Stirling Cycle machine having a cylinder mounted in a housing has a displacer reciprocably mounted in the cylinder. Also reciprocably mounted in the cylinder is a piston and passages are provided in the cylinder so that when the displacer moves in one direction, a cooled gas will be drawn into the cylinder between the displacer and the piston, and when the displacer moves in the opposite direction, a heated gas will be drawn into the cylinder to thus provide expansive gas forces working against the piston thus causing the piston to be driven in its power stroke when the machine is utilized as an engine. The piston is drivingly connected to a crankshaft and the displacer is driven by a crankshaft, which is in rotative synchronism such that the displacer movement in the cylinder in the direction to draw heated air into the cylinder overlaps in time a substantial portion of the piston power stroke.