Abstract: A two stroke cycle engine has an engine block with a cylinder bore accommodating a piston. An exhaust port connects the cylinder bore to an outside of the engine block. An exhaust port control valve mechanism within the engine, according to this invention, includes a valve pivotally mounted in the exhaust port between the cylinder bore and the outside for rotation between an open position and a closed position. The valve defines an upper timing edge of the exhaust port. An insert fills a volume in the exhaust port between the valve and the outside, thereby improving flow efficiency of the exhaust port.

Abstract: A two stroke cycle engine has tiered cooling jackets in the cylinder block with upper and lower jackets separated by a diaphragm wall. Transfer openings in the diaphragm and downward portions of the lower jacket direct coolant flow around exhaust ports and preferentially along the exhaust port side of the engine cylinder openings. A cylinder head gasket controls outflow from the upper jacket to the cylinder head through transfer holes placed preferably on the exhaust side of the upper jacket to provide overall control of flow in the cooling jacket system.

Abstract: A port scavenged two cycle engine with a separate source of pressurized air has a valve between each port and the air supply to provide a high blowdown pulsing scavenging flow to the cylinders similar to that of a crankcase scavenged engine. Various arrangements with additional features are disclosed.

Abstract: A two cycle engine has oil distribution means through the cylinder wall to feed internal oil passages in the associated piston that distribute oil directly to the skirt and cylinder walls, preferably between ports, and/or to the wrist pin and connecting rod bearing to thereby limit oil carryover into the engine charging and scavenging air.