Stirling engines

A Stirling Engine comprising a housing, a drive member, a cylinder defined within the housing whereby the housing defines a cylinder wall, an aperture defined in the cylinder wall, a piston mounted for reciprocation in the cylinder, a pivot bearing having a pivot axis fixed with respect to the housing, a connection between the piston and the drive member comprising a lever arm having two ends and being pivotally mounted about the pivot bearing intermediate the ends of the lever arm and extending through the aperture, and a gas seal arranged to prevent escape of pressure from the cylinder through the aperture around the lever arm, the seal comprising a part spherical seat on the lever arm with its centre coincident with the pivot axis, an annular seal member sealingly mounted with respect to the housing and having a part spherical sealing surface in sealing contact with the part spherical seat and means for urging the seal member into sealing engagement with the seat.