Abstract: A rotary valve system for use in internal combustion engines comprises an elongated substantially cylindrical valve passage means having a threaded section at one end and an outwardly extending disc portion at the other end. The outwardly extending lower portion includes a valve disc aperture for alternate communication with inlet and outlet passages in the valve disc jacket for predetermined time periods. The bottom of the disc portion comprises the upper surface of the combustion chamber and can include a shaped protrusion for purposes of charge stratification. Rotation means support the valve disc arrangement for rotation within the cylinder head or valve disc jacket about the longitudinal axis of the assembly. The inner recess of the valve disc jacket which contacts the outwardly extending valve disc is provided with a mating carbon, graphite or molybdenum impregnated sleeve insert.