The present invention comprises a rotary valve apparatus for internal combustion engines having a cylindrical outer casing, an inlet port and an outlet port on an outer wall thereof. The cylindrical outer casing having a bottom opening and dimensioned and configured to be secured over an engine cylinder. An inner rotor having a shaft with a first end and a second end, and a lower circular member at the second end. The first end having a plurality of vertical splines and the lower circular member having a cutout portion, a circular end cap having an inlet port and an outlet port disposed within the bottom opening of the outer casing. The inner rotor rotatably mounted on the circular end cap wherein the cutout portion can align with the inlet port or the outlet port and a gear assembly rotating the inner rotor.