a sliding exhaust control valve for two - stroke cycle engines is disclosed . this valve actuates at least partially through the exhaust passage and delays flow from the combustion chamber through the exhaust passage during the expansion stroke of the piston while permitting full opening of the exhaust passage and giving complete blow down before the scavenging cycle of the engine . also disclosed is a mechanical linkage mechanism between the slide valve and the crankshaft and cam controlled actuation means to provide precise control of the exhaust valve throughout the engine cycle .