Self lubricating, non-sealing piston ring for an internal combustion fastener driving tool

A piston assembly, comprising:

• a reciprocating piston axially movable within a cylinder;
• at least one sealing ring for sealing between an inner wall of the cylinder and the piston;
• and
• means for lubricating the inner wall of the cylinder, said means consisting essentially of a non-sealing ring positioned between the inner wall of the cylinder and the piston and axially spaced from said at least one sealing ring, said non-sealing ring being made at least partially of a low-friction wearable material transferable onto the inner wall of the cylinder during relative movement of said non-sealing ring and said inner wall of the cylinder
• wherein the non-sealing ring comprises first and second end faces spaced from each other by a thickness of said non-sealing ring in an axial direction of said piston assembly, the non-sealing ring further comprising
• an inner portion at least partially received in a groove formed on the piston;
• and
• an outer portion being made of said low-friction wearable material and extending radially from the inner portion, wherein said outer portion has a plurality of obliquely extending gas passages that connect the first and second end faces and extend through the entire thickness of said ring, thereby allowing gases contained in the cylinder to move through said outer portion to promote rotation of said non-sealing ring about the piston during axial movements of the piston within the cylinder.