Abstract: A rotary valve engine in which the rotary valve is located laterally of the cylinder and includes straight longitudinally extending, concentrically arranged intake and exhaust passages for unrestricted flow of air or combustible mixture into the cylinder or cylinders and exhaust of combustion products with the incoming air or combustible mixture being in heat exchange relation to the exhausting combustion products. The rotary valve includes an inner tubular exhaust member made in sections connected together with expansion joints, seal strips mounted in the bore of the valve case with the valve being suspended in the valve bore and the rotary valve being lubricated by a roller lubricating system.