This invention is a slotted cylindrical rotary valve assembly for an internal combustion engine, comprising of two sets of gear driven slotted cylindrical tubes in a cradle apparatus. Each set has two tubes located co-axially and rotates co-axially, and each tube is slotted to allow for improved transport of a fuel/air mixture and exhaust. In one embodiment, an intake set of tubes transport fuel/air through apertures on the tubes. The exhaust set of tubes transport exhaust through apertures (slots) on the tubes. The rotation of the tubes brings the apertures in timely alignment to allow fuel/air injection and exhaust in synchronization with the cyclical operation of the pistons in the combustion chambers. Effective sealing in one embodiment is achieved by using a modified piston with an extension wall extending longitudinally from the top of the piston to seal intake and exhaust orifices at the top of the chamber.