Abstract: The present invention provides a crankcase compression type two-cycle engine which has a comparatively simple construction, is capable of operating at a low fuel consumption and discharges an exhaust gas having a comparatively low hydrocarbon concentration. The engine comprises a crankcase, a piston, a cylinder joined to the crankcase and provided in its lower part with an exhaust port which is opened and closed by the piston, a cylinder head attached to the upper end of the cylinder, and forming a combustion chamber together with the cylinder and the piston. A poppet scavenging valve is provided in the upper part of the cylinder so as to be opened to the combustion chamber side. A diaphragm actuator operates the poppet scavenging valve using the pressure within the crankcase. The diaphragm actuator is provided with a diaphragm that receives the pressure within the crankcase on one side thereof and receives the pressure of a spring on the other side thereof.

Abstract: A 4-cycle internal combustion engine including a crankcase, a cylinder, a cylinder head, a piston adapted to reciprocate within the cylinder, a combustion chamber formed by the piston, the cylinder and the cylinder head, and a crankshaft connected to the piston via a connecting rod, is improved in order to enhance its thermal efficiency, to reduce exhaust emissions and to make it possible to operate the engine while the engine is in any attitude.

Abstract: For the purpose of preventing a decompression passageway in a two-cycle engine from being blocked by carbon soot, facilitating manufacture of a two-cycle engine having decompression structure and eliminating reduction of output power of the two-cycle engine caused by the decompression structure, a known two-cycle engine includes a scavenging passageway formed along an inner wall of a cylinder. The scavenging passageway is directed in the axial direction of the cylinder and communicates with a crank case of the engine. A decompression groove extends in the axial direction of the cylinder on the upstream side of a cylinder cooling airflow at a top end portion of the scavenging passageway. The width and depth of the decompression groove are either varied along the axial direction of the groove so as to be narrowed towards a tip end thereof directed toward a plug, or are provided with a narrowed portion of venturi shape.