A rotary valve engine is always a two stroke engine. Most rotary valve engines are rotax engines. Although other rotary engines such as suzuki and kawasaki have been made. Rotax engines are used in snowmobiles, jet-skis and motorcycles and aircraft engines. A rotary valve refers to the intake of a two stroke engine. There are three types of intake designs for two stroke engines. Simplistic two strokes are piston port, meaning that the piston movement past the port controls the incoming air timing. The piston port engine doesn’t do a very good job of keeping the airflow to stay in the engine. The air can simply travel back out of the engine. The most popular intake air induction is the reed port engine. It uses reed petals to allow the intake air in the engine and traps it there. The tension of the reed petals can change with the use of different petals and can provide some power improvement at certain rpm ranges. A rotary valve engine has the best intake air control.
The rotary valve rotates mechanically in a circular motion. This motion allows the intake port to be opened and closed at the best possible time. The rotary valve also allows the port to have no restriction such as the reeds cause. The timing of the rotary plate can be changed by the shape of the valve and is done in some racing engines. Most rotary valve engines are two cylinder engines that are driven off of a gear in the crankcase between the cylinders. Some three cylinder engines have been made with rotary valves but are too complex for a standard production engines. Rotary valve engines are a very good design with complete control of airflow into an engine. They also keep the air in without any airflow restrictions.