Abstract: An internal combustion engine for reducing the amount of bubbles contained in the circulated oil without reducing the ground clearance of the engine. A crankcase is provided therein with an oil suction passage makes an oil pump and an end part of a bottom wall of an oil sump chamber communicate with each other, passes between the oil sump chamber and a hanger boss, and has a lowest part located below the bottom wall of the oil sump chamber.

Abstract: An exhaust control device for a vehicle engine includes an exhaust control valve capable of changing the opening area of an exhaust passage. The exhaust control valve is disposed in exhaust passage forming means so as to be able to change a bent-internal side partial passage sectional area of the passage sectional area of an exhaust passage. Specifically the exhaust control valve is disposed at a bent portion of the exhaust passage that is closest to an exhaust valve port. With this configuration, the exhaust flow rate can be controlled satisfactorily.

Abstract: In a four-cycle engine, the stiffness of a rocker shaft support portion is increased while avoiding an increase in the size of a cylinder head. The rocker shaft support portion that supports a rocker shaft is integrally formed on the cylinder head so as to be disposed between an engine valve and a camshaft as viewed from an axial direction of the camshaft and the rocker shaft. First reinforcement ribs are integrally disposed in a protruding condition on a plane orthogonal to an axis of a rocker shaft on a side face of rocker shaft support portions opposite a side of a camshaft.

Abstract: An internal combustion engine for reducing the amount of bubbles contained in the circulated oil without reducing the ground clearance of the engine. A crankcase is provided therein with an oil suction passage makes an oil pump and an end part of a bottom wall of an oil sump chamber communicate with each other, passes between the oil sump chamber and a hanger boss, and has a lowest part located below the bottom wall of the oil sump chamber.

Abstract: In a four-cycle engine, the stiffness of a rocker shaft support portion is increased while avoiding an increase in the size of a cylinder head. The rocker shaft support portion that supports a rocker shaft is integrally formed on the cylinder head so as to be disposed between an engine valve and a camshaft as viewed from an axial direction of the camshaft and the rocker shaft. First reinforcement ribs are integrally disposed in a protruding condition on a plane orthogonal to an axis of a rocker shaft on a side face of rocker shaft support portions opposite a side of a camshaft.

Abstract: An exhaust control device for a vehicle engine includes an exhaust control valve capable of changing the opening area of an exhaust passage. The exhaust control valve is disposed in exhaust passage forming means so as to be able to change a bent-internal side partial passage sectional area of the passage sectional area of an exhaust passage. Specifically the exhaust control valve is disposed at a bent portion of the exhaust passage that is closest to an exhaust valve port. With this configuration, the exhaust flow rate can be controlled satisfactorily.

Abstract: An exhaust control device for a vehicle engine wherein an exhaust pipe forms an exhaust passage along with an exhaust port is connected to a cylinder head via the exhaust port. A rotary valve is capable of changing the opening area of the exhaust passage. The rotary valve being disposed in approximately the middle of the exhaust passage. The opening area of the exhaust passage is made controllable by the rotary valve while avoiding an increase in the number of component parts. A rotary valve having a turning axis located at a position offset from the center of the exhaust port is housed in a valve housing provided integrally with a cylinder head.

Abstract: An air cleaner device for a motorcycle including a cylindrical filter element disposed in a box of an air cleaner, wherein air purified by the element is sent to an air-intake system. Further, a rectifying member is disposed around the outer periphery of the cylindrical filter element at a predetermined distance apart therefrom and the rectifying member is formed into a cylindrical shape so as to cover the entire outer periphery of the element.

Abstract: An air cleaner device for a motorcycle including a cylindrical filter element disposed in a box of an air cleaner, wherein air purified by the element is sent to an air-intake system. Further, a rectifying member is disposed around the outer periphery of the cylindrical filter element at a predetermined distance apart therefrom and the rectifying member is formed into a cylindrical shape so as to cover the entire outer periphery of the element.