A Stirling cycle machine comprising: a rocking beam having a rocker pivot; at least one cylinder, wherein the cylinder further comprises a closed end and an open end, wherein the open end further comprises a linear bearing connected to the cylinder, the linear bearing having an opening; at least one piston, the piston housed within a respective cylinder whereby the piston is capable of substantially linearly reciprocating within the respective cylinder; and at least one coupling assembly having a proximal end and a distal end, the proximal end being connected to the piston and the distal end being connected to the rocking beam by an end pivot, whereby linear motion of the piston is converted to rotary motion of the rocking beam, wherein the coupling assembly further comprises a piston rod and a link rod, the piston rod and link rod coupled together by a coupling means, the coupling means being located along the linear bearing, wherein the opening of the linear bearing is configured to accommodate the coupling assembly; a crankcase housing the rocking beam and housing a first portion of the coupling assembly; a crankshaft coupled to the rocking beam by way of a connecting rod, whereby the rotary motion of the rocking beam is transferred to the crank shaft; a working space housing the at least one cylinder, the at least one piston and a second portion of the coupling assembly; and characterised by: a seal being sealably connected to the piston rod, and wherein the seal is a rolling diaphragm comprising elastomeric material with fibers dispersed therein,wherein the seal is configured to seal the working space from the crankcase to maintain a lubricating fluid in the crankcase; an airlock located between the crankcase and the working space, the airlock being in fluid communication with the working space so that the pressure within the airlock is equal to the mean pressure of the working space, wherein the airlock is arranged above the rolling diaphragm, and the crankcase is arranged below the rolling diaphragm; and a pressure regulator configured to maintain a constant pressure differential between the airlock and the crankcase. a rocking beam having a rocker pivot; at least one cylinder, wherein the cylinder further comprises a closed end and an open end, wherein the open end further comprises a linear bearing connected to the cylinder, the linear bearing having an opening; at least one piston, the piston housed within a respective cylinder whereby the piston is capable of substantially linearly reciprocating within the respective cylinder; and at least one coupling assembly having a proximal end and a distal end, the proximal end being connected to the piston and the distal end being connected to the rocking beam by an end pivot, whereby linear motion of the piston is converted to rotary motion of the rocking beam, wherein the coupling assembly further comprises a piston rod and a link rod, the piston rod and link rod coupled together by a coupling means, the coupling means being located along the linear bearing, wherein the opening of the linear bearing is configured to accommodate the coupling assembly; a seal being sealably connected to the piston rod, and wherein the seal is a rolling diaphragm comprising elastomeric material with fibers dispersed therein,wherein the seal is configured to seal the working space from the crankcase to maintain a lubricating fluid in the crankcase; an airlock located between the crankcase and the working space, the airlock being in fluid communication with the working space so that the pressure within the airlock is equal to the mean pressure of the working space, wherein the airlock is arranged above the rolling diaphragm, and the crankcase is arranged below the rolling diaphragm; and a pressure regulator configured to maintain a constant pressure differential between the airlock and the crankcase.