Abstract: An internal combustion engine is equipped with a variable valve control system which is operable to selectively actuate an engine valve using one of two cams of a camshaft, by sliding a rocker arm in the axial direction of a rocker-arm shaft. The system is capable of restricting the axial-direction movement of the rocker arm within a predetermined range, using a simple structure without unduly increasing the number of component parts. Position-restriction portions are formed in a rocker arm, and abut on a trigger arm to restrict sliding movement of the rocker arm within a predetermined amount, when the trigger arm is disengaged from the rocker arm.

Abstract: A crankcase having a mounting structure configured to receive an oil level sight glass fitted on a lower outer portion of the crankcase in a through hole formed therein, and a retainer member clamped to an outer surface of the crankcase to prevent the oil level sight glass from falling off. An outwardly protrudingly rib is formed on the outer portion of the crankcase which is engaged with a cut formed on the retainer member to securely position the retainer member on the crankcase. The retainer member includes a scale mark provided thereon, and the oil level sight glass permits visual observation for checking an oil level of oil held in an oil reservoir disposed at the lower portion of the crankcase.

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: A breather apparatus for an internal combustion engine which, when casting a cylinder head cover, can improve the fluidity of molten metal and promote gas-liquid separation through effective use of an entire breather chamber. A breather apparatus for an internal combustion engine has a cylinder head cover in which a breather chamber is formed. In the breather chamber, a number of ribs extend from a side wall included in a peripheral wall of the chamber obliquely relative to a direction in which blowby gas flows in through inflow ports. The ribs extend up to where they are continuous with respective fixing bosses. The ribs include projecting lower edge portions which are partly cut out, forming respective concave portions.

Abstract: In an oil cooler, a heat exchange core is housed in a casing including a cylindrical sidewall part in a way that a cooling water passage is formed around a heat exchange core. The heat exchange core includes inlet-side and outlet-side oil passages, and enables oil to be delivered from the inlet-side oil passage to the outlet-side oil passage. Inlet and outlet pipes are connected to the sidewall part. The inlet pipe forms a cooling water inlet passage in communication with the cooling water passage. The outlet pipe forms a cooling water outlet passage in communication with the cooling water passage. Outward of the inlet-side oil passage, an outwardly swelling part is formed in the sidewall part of the casing. This arrangement avoids the oil cooler being constructed in a large size and avoids decreasing the heat exchange efficiency of the oil cooler, and also prevents cavitation and erosion from occurring due to the flow of cooling water in an area corresponding to the inlet-side oil passage.

Abstract: A transmission structure of a power unit for a vehicle includes a clutch mechanism that is provided between a crankshaft and a main shaft, and is installed at the end of the main shaft outside a crankcase. The transmission includes a shift drum for driving shift forks for selectively establishing any of plural speeds. Both ends in an axial direction of the shift drum are rotatably supported by the crankcase. In the transmission structure, a sealed structure dedicated to the shift drum is not required, the number of parts is reduced and the assembly time is reduced. The shift drum, arranged in the maximum outside diameter of the clutch mechanism when viewed in a plane perpendicular to the axis of the main shaft, is assembled in the crankcase from the side of the clutch mechanism.

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: A breather apparatus for an internal combustion engine which, when casting a cylinder head cover, can improve the fluidity of molten metal and promote gas-liquid separation through effective use of an entire breather chamber. A breather apparatus for an internal combustion engine has a cylinder head cover in which a breather chamber is formed. In the breather chamber, a number of ribs extend from a side wall included in a peripheral wall of the chamber obliquely relative to a direction in which blowby gas flows in through inflow ports. The ribs extend up to where they are continuous with respective fixing bosses. The ribs include projecting lower edge portions which are partly cut out, forming respective concave portions.

Abstract: A crankcase having a mounting structure configured to receive an oil level sight glass fitted on a lower outer portion of the crankcase in a through hole formed therein, and a retainer member clamped to an outer surface of the crankcase to prevent the oil level sight glass from falling off. An outwardly protrudingly rib is formed on the outer portion of the crankcase which is engaged with a cut formed on the retainer member to securely position the retainer member on the crankcase. The retainer member includes a scale mark provided thereon, and the oil level sight glass permits visual observation for checking an oil level of oil held in an oil reservoir disposed at the lower portion of the crankcase.

Abstract: An internal combustion engine in a power unit includes an oil pump that rotates by a transmission mechanism with an endless chain, and a crankcase with an opening formed by protruding walls of side walls of the crankcase in an axial direction. A drive sprocket is fitted to a main shaft of a gear transmission and a driven sprocket is fitted to a shaft end of a drive shaft of an oil pump. When viewed sideways, the protruding walls and mating faces have overlapping parts that partially overlap the driven sprocket. On the other hand, all the shaft end and the remainder of the driven sprocket are exposed inside the opening when the cover is removed. The resulting configuration improves the working efficiency in fitting an oil pump into the crankcase without reducing the rigidity of the crankcase.

Abstract: A lubrication system of a vehicle engine wherein a cylinder head has a head side oil passage disposed at one end thereof along the axis of a crankshaft. A lower case of a crankcase is provided with a supply source side oil passage communicating with an oil supply source and extending parallel to the axis of the crankshaft and a branched oil passage guiding oil to the head side oil passage which branches from the supply source side oil passage and extends upwardly. An upper case side oil passage extending vertically to communicate with a head side oil passage is provided at one end of an upper case along the axis of the crankshaft. A communication passage communicating the upper end of a branched oil passage is provided in a lower case in a position inwardly from the upper case side oil passage along the axis of the crankshaft.

Abstract: A cooling structure is a separate member from a structural portion of an engine. An oil injection pipe includes cooling oil injection holes for injecting cooling oil into cylinder bores and is mounted across an engine at a somewhat upper position with respect to a crank shaft and in parallel with the crank shaft. Both ends of the oil injection pipe are fixed through mounting members to right and left side walls of the engine, whereby the pipe is mounted. Two left and right pipe portions are joined together at a central position between the two to constitute the oil injection pipe as a single pipe. At the connection in the central position, the oil injection pipe is connected to an oil supply path. Oil supplied through the oil supply path flows into the left and right pipe portions and is injected from the injection holes into the cylinder bores.

Abstract: In a power unit, a counter shaft of a transmission and a crank shaft of an internal combustion engine, both located below a main shaft of the transmission, are arranged parallel to each other on a separating plane H of a crankcase. In a transmission mechanism T which drives an oil pump located below the separating plane H, a drive sprocket is placed on the main shaft of the transmission and a driven sprocket is placed on a drive shaft of the oil pump. An endless chain slidably touches a slender long chain guide along the running direction of the endless chain. The chain guide is fitted only to an end wall of an upper crankcase at its fitting part. The chain guide stretches across the end wall of the upper crankcase and an end wall of a lower crankcase, and effectively suppresses vibration of the endless chain.

Abstract: A vehicular power unit including a drive-side transmission sprocket wheel provided on an end of an output shaft that protrudes from one side of a crankcase, an endless transmission belt for transmitting power to a driving wheel wound the sprocket wheel. The endless transmission belt transmits power from the crankshaft to a transmission housed in the crankcase. A water pump is arranged on the same side of the crankcase in a position between the crankshaft and the output shaft. Further, the water pump is disposed inside the drive-side transmission sprocket wheel in a direction along the axis of an output shaft. This configuration enables the vehicular power unit to be formed in a compact size in a direction along an axis of a crankshaft.

Abstract: A lubrication system of a vehicle engine wherein a cylinder head has a head side oil passage disposed at one end thereof along the axis of a crankshaft. A lower case of a crankcase is provided with a supply source side oil passage communicating with an oil supply source and extending parallel to the axis of the crankshaft and a branched oil passage guiding oil to the head side oil passage which branches from the supply source side oil passage and extends upwardly. An upper case side oil passage extending vertically to communicate with a head side oil passage is provided at one end of an upper case along the axis of the crankshaft. A communication passage communicating the upper end of a branched oil passage is provided in a lower case in a position inwardly from the upper case side oil passage along the axis of the crankshaft.

Abstract: An internal combustion engine in a power unit includes an oil pump that rotates by a transmission mechanism with an endless chain, and a crankcase with an opening formed by protruding walls of side walls of the crankcase in an axial direction. A drive sprocket is fitted to a main shaft of a gear transmission and a driven sprocket is fitted to a shaft end of a drive shaft of an oil pump. When viewed sideways, the protruding walls and mating faces have overlapping parts that partially overlap the driven sprocket. On the other hand, all the shaft end and the remainder of the driven sprocket are exposed inside the opening when the cover is removed. The resulting configuration improves the working efficiency in fitting an oil pump into the crankcase without reducing the rigidity of the crankcase.

Abstract: A vehicular power unit including a drive-side transmission sprocket wheel provided on an end of an output shaft that protrudes from one side of a crankcase, an endless transmission belt for transmitting power to a driving wheel wound the sprocket wheel. The endless transmission belt transmits power from the crankshaft to a transmission housed in the crankcase. A water pump is arranged on the same side of the crankcase in a position between the crankshaft and the output shaft. Further, the water pump is disposed inside the drive-side transmission sprocket wheel in a direction along the axis of an output shaft. This configuration enables the vehicular power unit to be formed in a compact size in a direction along an axis of a crankshaft.

Abstract: A transmission structure of a power unit for a vehicle includes a clutch mechanism that is provided between a crankshaft and a main shaft, and is installed at the end of the main shaft outside a crankcase. The transmission includes a shift drum for driving shift forks for selectively establishing any of plural speeds. Both ends in an axial direction of the shift drum are rotatably supported by the crankcase. In the transmission structure, a sealed structure dedicated to the shift drum is not required, the number of parts is reduced and the assembly time is reduced. The shift drum, arranged in the maximum outside diameter of the clutch mechanism when viewed in a plane perpendicular to the axis of the main shaft, is assembled in the crankcase from the side of the clutch mechanism.

Abstract: A cooling structure is a separate member from a structural portion of an engine. An oil injection pipe includes cooling oil injection holes for injecting cooling oil into cylinder bores and is mounted across an engine at a somewhat upper position with respect to a crank shaft and in parallel with the crank shaft. Both ends of the oil injection pipe are fixed through mounting members to right and left side walls of the engine, whereby the pipe is mounted. Two left and right pipe portions are joined together at a central position between the two to constitute the oil injection pipe as a single pipe. At the connection in the central position, the oil injection pipe is connected to an oil supply path. Oil supplied through the oil supply path flows into the left and right pipe portions and is injected from the injection holes into the cylinder bores.

Abstract: To enable a change spindle to be always operated as a driver wishes by providing an alternative selection of a motor change mode and a manual change mode. A change motor and a change manipulating member are arranged such that they can be connected to a change spindle of a transmission in parallel. Mode changeover means which can be changed over between a motor change mode position (A) which enables the operation of the change spindle only by the change motor and a manual change mode position (B) which enables the operation of the change spindle only by the change manipulating member is disposed between the change spindle and the change motor and the change manipulating member.