Abstract: An internal combustion engine having a cylindrical outer housing with inner cylindrical cylinders defining power cylinders circumferentially spaced in the engine. Each of the cylinder(s) has opposed intake and exhaust pistons. The intake and exhaust pistons use air bearings instead of conventional oil as a lubricant. The intake and exhaust pistons power a rotary cam mounted on opposed ends of the engine and a cam follower system positions the pistons. The rotary cam is operatively connected to a drive shaft or power take off shaft. A four bar linkage system is connected to the piston rod to minimize piston side loads. A jumper connects the ends of the power cylinders to pressurize air drawn into the engine and to admit heated air, indirectly heated during the combustion cycle, to charge the power cylinder for improved efficiency and to purge the pressure cylinder after combustion.