An exhaust timing control system for two-cycle engines includes a pivotally mounted valve body on which the timing control surface is formed on a ridge-defining element positioned at the free end of a plate having reduced thickness for weight reduction purposes. The valve body is protected against thermal stresses by reception in a recess of conforming shape located in the upper surface of the exhaust passage. The component parts of the system may be provided with various structural configurations to enhance the system's operational efficiency.