Abstract: In an internal combustion engine including a driving-sprocket cam chain guide 70 for guiding a cam chain 47 along a driving sprocket 45, as viewed in a crankshaft axial direction, a guide body 71 of the driving-sprocket cam chain guide 70 extends beyond a winding termination point P of the cam chain 47 on the driving sprocket 45 to a position adjacent to a chain moving surface 51c of a cam chain tensioner 51, on which the cam chain 47 slides. The engine provides a cam-chain dropout preventing function to the cam chain guide, thus reducing load on the cam chain tensioner and improving durability of the tensioner lifter.

Abstract: In an internal combustion engine including a driving-sprocket cam chain guide 70 for guiding a cam chain 47 along a driving sprocket 45, as viewed in a crankshaft axial direction, a guide body 71 of the driving-sprocket cam chain guide 70 extends beyond a winding termination point P of the cam chain 47 on the driving sprocket 45 to a position adjacent to a chain moving surface 51c of a cam chain tensioner 51, on which the cam chain 47 slides. The engine provides a cam-chain dropout preventing function to the cam chain guide, thus reducing load on the cam chain tensioner and improving durability of the tensioner lifter.

Abstract: Enhanced combustibility by increasing the difference in intake gas velocity between a low flow velocity region and first and second high flow velocity regions in an intake port. An intake port of an internal combustion engine has an intake flow control port portion provided with first and second projecting portions. In the passage cross section of the intake flow control port portion, there are provided a low flow velocity region, and first and second high flow velocity regions formed on either side of and across the low flow velocity region and the first and second projecting portions wherein the maximum flow velocity of intake gas is comparatively larger than that in the low flow velocity region. The intake gas reaches intake ports with a flow velocity distribution having the relationship of the magnitudes of flow velocities in the low flow velocity region and first and second high flow velocity regions.

Abstract: Enhanced combustibility by increasing the difference in intake gas velocity between a low flow velocity region and first and second high flow velocity regions in an intake port. An intake port of an internal combustion engine has an intake flow control port portion provided with first and second projecting portions. In the passage cross section of the intake flow control port portion, there are provided a low flow velocity region, and first and second high flow velocity regions formed on either side of and across the low flow velocity region and the first and second projecting portions wherein the maximum flow velocity of intake gas is comparatively larger than that in the low flow velocity region. The intake gas reaches intake ports with a flow velocity distribution having the relationship of the magnitudes of flow velocities in the low flow velocity region and first and second high flow velocity regions.

Abstract: To provide an aluminum alloy member having a high machinability while keeping a sufficient mechanical strength and a sufficient wear resistance, and a method of producing the aluminum alloy member. In an aluminum alloy member formed from an aluminum-silicon alloy by casting, eutectic silicon grains are exposed from at least part of an exposed plane of the aluminum alloy member. A coating layer having a thickness nearly equal to or thinner than a diameter of each of the eutectic silicon grains is formed on the exposed plane from which the eutectic silicon grains are exposed.

Abstract: It is intended to provide an exhaust control system in a two-cycle internal combustion engine capable of suppressing the occurrence of irregular combustion when an opening timing of an exhaust port is set to a maximum delay timing, thereby improving the combustion stability and affording a high engine output when the opening timing of the exhaust port is set to a maximum advance timing. In the exhaust control system, an exhaust control valve has valve elements movable between their maximum projected positions at which a maximum delay timing of the exhaust ports is set and their maximum retracted positions at which a maximum advance timing of the exhaust ports is set. The valve elements are provided with control surfaces, that face a cylinder bore at the maximum projected positions of the valve elements to close upper port portions of the exhaust ports.

Abstract: A common drive shaft for first and second exhaust control valves is formed of a single piece. A first exhaust valve adjusting exhaust timing and a second exhaust valve adjusting a sectional area of an exhaust passage are provided on the common drive shaft. The second exhaust valve is rotated integrally with the drive shaft. The first exhaust valve is fitted on the drive shaft via an intermediate sleeve and a torsion coil spring. A linkage mechanism is provided so that the intermediate sleeve is stopped at a limit of rotation of the first exhaust valve. Thereafter, only the second exhaust valve is rotated.

Abstract: It is intended to provide an exhaust control system in a two-cycle internal combustion engine capable of suppressing the occurrence of irregular combustion when an opening timing of an exhaust port is set to a maximum delay timing, thereby improving the combustion stability and affording a high engine output when the opening timing of the exhaust port is set to a maximum advance timing. In the exhaust control system, an exhaust control valve has valve elements movable between their maximum projected positions at which a maximum delay timing of the exhaust ports is set and their maximum retracted positions at which a maximum advance timing of the exhaust ports is set. The valve elements are provided with control surfaces, that face a cylinder bore at the maximum projected positions of the valve elements to close upper port portions of the exhaust ports.

Abstract: A common drive shaft for first and second exhaust control valves is formed of a single piece. A first exhaust valve adjusting exhaust timing and a second exhaust valve adjusting a sectional area of an exhaust passage are provided on the common drive shaft. The second exhaust valve is rotated integrally with the drive shaft. The first exhaust valve is fitted on the drive shaft via an intermediate sleeve and a torsion coil spring. A linkage mechanism is provided so that the intermediate sleeve is stopped at a limit of rotation of the first exhaust valve. Thereafter, only the second exhaust valve is rotated.

Abstract: To provide an aluminum alloy member having a high machinability while keeping a sufficient mechanical strength and a sufficient wear resistance, and a method of producing the aluminum alloy member. In an aluminum alloy member formed from an aluminum-silicon alloy by casting, eutectic silicon grains are exposed from at least part of an exposed plane of the aluminum alloy member. A coating layer having a thickness nearly equal to or thinner than a diameter of each of the eutectic silicon grains is formed on the exposed plane from which the eutectic silicon grains are exposed.

Abstract: An exhaust control valve assembly for a two-cycle engine includes a governor for moving an exhaust control valve in opening and closing directions to advance or retard a timing of opening of an exhuast port. The governor includes a governor spring for urging the exahust control valve in the closing direction. The governor spring exhibits a changing spring constant which increases as the exhaust control valve moves in the opening direction.

Abstract: An exhaust control valve assembly for a two-cycle engine is formed to effectively dissipate heat. The exhaust control valve includes a pair of valve elements disposed on opposite sides of a reinforcing wall. The reinforcing wall laterally bisects an opening of the exhaust port in a vertical direction. A valve stem is connected to bosses of the valve elements. The valve stem is supported in a rotatable manner by a pouch-shaped hole at one end and a through-hole at its other end. A drive system is coupled to an end part of the valve stem protruding outwards from the through-hole. The whole of the bosses of the valve elements is offset from the center of the reinforcing wall towards the through-hole. This arragnement allows heat, resulting from the exhaust gases passing by the valve elements, to be dissipate without overheating the valve stem on the pouch-shaped hole side.