Abstract: A base-material hole is formed in a connecting-rod base material. A coating layer is deposited on an inner peripheral surface of the base-material hole. The base-material hole 15 has a cylinder inner-surface portion of a constant inner diameter, formed in a central region in an axial direction, and a tapered inner-surface portion that is continuous with an axially outer side of the cylinder inner-surface portion and is radially enlarged in an axially outward direction. The coating layer has a first coating portion and a second coating portion deposited on the tapered inner-surface portion to adjoin the first coating portion and gradually increasing in material thickness in the axially outward direction.

Abstract: An oil passage of an internal combustion engine including a crankcase, a cylinder block integrally connected to the crankcase, a piston operatively mounted within the cylinder block, a piston jet for providing oil to the piston within the cylinder block and a breather device integrally formed on the cylinder block wherein the breather device is in communication with the inside of the crankcase. An elevation of temperature of the oil which flows in an oil supply path is prevented thus allowing oil in the oil supply path to maintain a low temperature wherein the oil in the supply path is supplied to a piston jet formed on the internal combustion engine. An oil supply path through which oil is supplied to the piston jet is integrally formed on a wall body exposed to ambient air on a peripheral wall which forms the breather device.

Abstract: A base-material hole is formed in a connecting-rod base material. A coating layer is deposited on an inner peripheral surface of the base-material hole. The base-material hole 15 has a cylinder inner-surface portion of a constant inner diameter, formed in a central region in an axial direction, and a tapered inner-surface portion that is continuous with an axially outer side of the cylinder inner-surface portion and is radially enlarged in an axially outward direction. The coating layer has a first coating portion and a second coating portion deposited on the tapered inner-surface portion to adjoin the first coating portion and gradually increasing in material thickness in the axially outward direction.

Abstract: A power unit for a motorcycle includes an internal combustion engine with a transmission having an input shaft and an output shaft. A clutch with a hydraulic cylinder is provided for changing over the connection/disconnection of power transmission between a crankshaft and the input shaft. A cylinder support member, mounted on the engine body, includes a cylindrical case portion where a portion of the hydraulic cylinder is housed. The power unit can be miniaturized by suppressing the projection of the hydraulic cylinder from the engine body in the axial direction. A cover member is mounted on the engine body for covering and surrounding a projecting end portion of an output shaft from an engine body. A cylinder support member is mounted on the engine body such that a portion of a case portion is arranged in an opening portion formed by cutting away a portion of the cover member.

Abstract: A crankshaft for an internal combustion engine can be an integrated crankshaft in which a thrust receiving surface is formed on each of crank arm parts around the root of a crankpin in an annularly protruding manner to restrict axial movement of a connecting rod. A recessed portion is formed in each of the facing surfaces of facing crank webs at a position near a corner portion continuing from the crankpin to the crank arm part, the position being so close to the crankpin that part of the thrust receiving surface is cut away.

Abstract: An internal combustion engine includes, among other things, a backlash adjusting device. An eccentric supporting shaft is disposed in an internal combustion engine so as to be able to be fixed at a predetermined rotational angle position about a central axis. The shaft adjusts an amount of clearance between a pair of gears, and is fitted over a base shaft fixed to the internal combustion engine such that the central axis of the eccentric supporting shaft coincides with an axis of the base shaft. An adjusting portion allows an inner circumference of the eccentric shaft to be fitted over an outer circumference of the base shaft at a predetermined rotational angle position. A fixing portion is configured to fix the eccentric supporting shaft to the base shaft.

Abstract: An oil passage of an internal combustion engine including a crankcase, a cylinder block integrally connected to the crankcase, a piston operatively mounted within the cylinder block, a piston jet for providing oil to the piston within the cylinder block and a breather device integrally formed on the cylinder block wherein the breather device is in communication with the inside of the crankcase. An elevation of temperature of the oil which flows in an oil supply path is prevented thus allowing oil in the oil supply path to maintain a low temperature wherein the oil in the supply path is supplied to a piston jet formed on the internal combustion engine. An oil supply path through which oil is supplied to the piston jet is integrally formed on a wall body exposed to ambient air on a peripheral wall which forms the breather device.

Abstract: A power unit for a motorcycle includes an internal combustion engine with a transmission having an input shaft and an output shaft. A clutch with a hydraulic cylinder is provided for changing over the connection/disconnection of power transmission between a crankshaft and the input shaft. A cylinder support member, mounted on the engine body, includes a cylindrical case portion where a portion of the hydraulic cylinder is housed. The power unit can be miniaturized by suppressing the projection of the hydraulic cylinder from the engine body in the axial direction. A cover member is mounted on the engine body for covering and surrounding a projecting end portion of an output shaft from an engine body. A cylinder support member is mounted on the engine body such that a portion of a case portion is arranged in an opening portion formed by cutting away a portion of the cover member.

Abstract: A water-cooled V-type engine includes a first coolant passage for supplying a liquid coolant discharged from a water pump disposed proximate a first cylinder, to a water jacket of the first cylinder. The engine also includes a second coolant passage which is branched off from the first coolant passage, and which is provided for supplying coolant to a water jacket of a second cylinder. The engine design allows for a shortened coolant hose. The water pump may include an integral fluid conduit including a branching portion where said second coolant supply passage is branched from said first coolant supply passage, and a restricted portion proximate the branching portion. A motorcycle including a vehicle body frame is also described, where the water-cooled V-type engine is operatively attached to the vehicle body frame.

Abstract: An internal combustion engine includes, among other things, a backlash adjusting device. An eccentric supporting shaft is disposed in an internal combustion engine so as to be able to be fixed at a predetermined rotational angle position about a central axis. The shaft adjusts an amount of clearance between a pair of gears, and is fitted over a base shaft fixed to the internal combustion engine such that the central axis of the eccentric supporting shaft coincides with an axis of the base shaft. An adjusting portion allows an inner circumference of the eccentric shaft to be fitted over an outer circumference of the base shaft at a predetermined rotational angle position. A fixing portion is configured to fix the eccentric supporting shaft to the base shaft.

Abstract: The present invention reduces weight while assuring required rigidity of a piston reduces cost of the piston. A piston includes first and second pin bosses supporting a piston pins, a first side wall coupling the first pin boss and a piston skirt, a second side wall coupling the second pin boss and the piston skirt, and a pair of bridges coupling the first and second side walls and forming upward spaces just above. First and second through holes are formed in the first and second side walls. The first and second through holes and the upper spaces are formed by a single punching process using a punch and, simultaneously, the bridges are formed.

Abstract: A water-cooled V-type engine includes a first coolant passage for supplying a liquid coolant discharged from a water pump disposed proximate a first cylinder, to a water jacket of the first cylinder. The engine also includes a second coolant passage which is branched off from the first coolant passage, and which is provided for supplying coolant to a water jacket of a second cylinder. The engine design allows for a shortened coolant hose. The water pump may include an integral fluid conduit including a branching portion where said second coolant supply passage is branched from said first coolant supply passage, and a restricted portion proximate the branching portion. A motorcycle including a vehicle body frame is also described, where the water-cooled V-type engine is operatively attached to the vehicle body frame.

Abstract: A power unit case for a power unit, including an internal combustion engine and a transmission, makes it possible to enhance the lubrication of a desired meshing portion of a group of transmission gears, while reducing the size of the engine. In the power unit case, a main shaft is arranged above a space between a crankshaft and a counter shaft arranged at a position substantially horizontally behind the crankshaft. A gear-ratio selecting member is arranged above a group of transmission gears on the counter shaft whose upper portion rotates toward a meshing portion between groups of transmission gears, and a lubricating projection that projects downwardly is formed in the transmission case above each of the transmission gears on the counter shaft and at a location on a ceiling surface of the transmission case where the gear-ratio selecting member is supported.

Abstract: The present invention reduces weight while assuring required rigidity of a piston reduces cost of the piston. A piston includes first and second pin bosses supporting a piston pins, a first side wall coupling the first pin boss and a piston skirt, a second side wall coupling the second pin boss and the piston skirt, and a pair of bridges coupling the first and second side walls and forming upward spaces just above. First and second through holes are formed in the first and second side walls. The first and second through holes and the upper spaces are formed by a single punching process using a punch and, simultaneously, the bridges are formed.

Abstract: A starter-motor mounting structure is provided in a wall of an engine case, in which a front mounting boss is formed in a rear inclined surface of an inclined cylinder block portion that projects from a crankcase. A rear mounting boss is formed in a front wall surface of a raised portion where an upper wall of a transmission case is raised upwardly to accommodate a main shaft that is positioned higher than a counter shaft. The front mounting boss and the rear mounting boss are offset from each other in the crankshaft direction. Front and rear brackets of a starter motor are fastened to the front mounting boss and to the rear mounting boss, respectively. This arrangement enables a starter motor to be securely mounted to a power unit case with high rigidity, while enabling a reduction in the size of the internal combustion engine.

Abstract: An engine cooling apparatus includes a cooling water outlet communicating with a water jacket provided in a cylinder block and a cylinder head provided on an intake port side of the cylinder head. A thermostat switches a path for cooling water discharged from the cooling water outlet, according to a cooling water temperature. A thermostat case for the thermostat is disposed downward of a line L extended from a coupling surface between a cylinder block and a cylinder head. The thermostat case and the cooling water outlet are connected via a connecting pipe. This arrangement makes it easy to secure a space for disposing the thermostat.

Abstract: A power unit case for a power unit, including an internal combustion engine and a transmission, makes it possible to enhance the lubrication of a desired meshing portion of a group of transmission gears, while reducing the size of the engine. In the power unit case, a main shaft is arranged above a space between a crankshaft and a counter shaft arranged at a position substantially horizontally behind the crankshaft. A gear-ratio selecting member is arranged above a group of transmission gears on the counter shaft whose upper portion rotates toward a meshing portion between groups of transmission gears, and a lubricating projection that projects downwardly is formed in the transmission case above each of the transmission gears on the counter shaft and at a location on a ceiling surface of the transmission case where the gear-ratio selecting member is supported.

Abstract: A starter-motor mounting structure is provided in a wall of an engine case, in which a front mounting boss is formed in a rear inclined surface of an inclined cylinder block portion that projects from a crankcase. A rear mounting boss is formed in a front wall surface of a raised portion where an upper wall of a transmission case is raised upwardly to accommodate a main shaft that is positioned higher than a counter shaft. The front mounting boss and the rear mounting boss are offset from each other in the crankshaft direction. Front and rear brackets of a starter motor are fastened to the front mounting boss and to the rear mounting boss, respectively. This arrangement enables a starter motor to be securely mounted to a power unit case with high rigidity, while enabling a reduction in the size of the internal combustion engine.

Abstract: An engine cooling apparatus includes a cooling water outlet communicating with a water jacket provided in a cylinder block and a cylinder head provided on an intake port side of the cylinder head. A thermostat switches a path for cooling water discharged from the cooling water outlet, according to a cooling water temperature. A thermostat case for the thermostat is disposed downward of a line L extended from a coupling surface between a cylinder block and a cylinder head. The thermostat case and the cooling water outlet are connected via a connecting pipe. This arrangement makes it easy to secure a space for disposing the thermostat.