A drive mechanism for a Stirling engine includes a piston rod, a displacer rod, a first crankshaft and a second crankshaft. The piston rod has a first end and a second end. The first end of the piston rod is configured to be coupled to a power piston of the Stirling engine. The displacer rod has a first end and a second end, the first end being configured to be coupled to a displacer piston of the Stirling engine. A rhombic drive mechanism comprises a plurality of pivotally connected connection members. The rhombic drive mechanism is configured to convert the linear movement of the piston rod to rotational movement of the first and second crankshaft and to convert linear movement of the piston rod to movement of the displacer rod. A guide is configured to substantially prevent lateral motion while allowing axial movement of at least one of the displacer rod and the piston rod.