Abstract: An orbit internal combustion engine having a housing with a cylindrical internal wall surrounding a plurality of combustion chambers. A plurality of pairs of intake and exhaust valves mounted on the housing control the flow of an air and fuel mixture into and exhaust gases out of the combustion chambers. A piston mounted on the shaft has a primary eccentric that supports the piston in the combustion chambers. A pair of secondary eccentrics spaced from the primary eccentric are mounted on the piston and housing to control the orbital movement of the piston. Seal assemblies slidably mounted in slots in the piston engage the cylindrical internal wall of the housing to form separate combustion chambers. The housing has arcuate slots non-concentric with its cylindrical internal wall accommodating axles on the seal assemblies to maintain the seal assemblies in constant and substantially uniform sealing engagement with the internal wall of the housing.