Abstract: A crankcase structure of an internal combustion engine has a desirable shaft support achieved by maintaining the strength of a side wall of a crankcase at a high level without increasing the weight and the size of the internal combustion engine even when the internal combustion engine has an output shaft projecting from the crankcase. A crankcase structure has a crankshaft and a counter shaft that are rotatably supported on a partitioning plane of a crankcase. A main shaft is oriented in the fore-and-aft direction and is rotatably supported on opposed front and rear walls of either one of the upper and lower crankcases. An output shaft to be driven by a power of the counter shaft penetrates through the front and rear walls of one of the upper and lower crankcases by which the main shaft is not rotatably supported, and projects to the front and rear.

Abstract: An outer circumference of a shift drum of a vehicle transmission is provided with at least one particular lead groove among multiple lead grooves which continuously extends beyond one circle of the shift drum. Two ends of the particular lead groove are arranged so as to be out of alignment with each other in the axial direction of the shift drum. A common shift position adapted to establish gear trains with two shift stages different from each other is set at one position corresponding to the two ends of the particular lead groove along the circumferential direction of the shift drum. The resulting configuration prevents an increase in the diameter of a shift drum and eliminates the significant change of the shape of a lead groove, even as the number of shift positions set on the shift drum is increased.

Abstract: A water-cooled internal combustion engine configured so as to facilitate the change of the cooling system, thereby reducing costs. The crankcase of the water-cooled internal combustion engine is adapted to journal a crankshaft. The crankcase is covered by a crankcase cover from the axial outside. The crankcase is connected to the crankcase cover through an annular shaped spacer, and at least part of a water pump is formed integrally with the spacer.

Abstract: To reduce the engaging sound to a low level, generated at the time of changing over the change gear stage by sliding a shifter, an intermittent feed mechanism includes a drum shifter, a pair of pawls symmetrically mounted to the drum shifter and energized in tilting-up directions, engaging recesses provided at regular intervals along the circumferential direction at the inner periphery of a shift drum center so as to be capable of engagement with both the pawls, and a fixed guide plate for guiding the tilted conditions of both the pawls. The guide plate is provided with a large-diameter arcuate part, a small-diameter arcuate part, and connecting parts. The pawls are engaged with the engaging recesses by the connecting parts, in the course of turning of the drum shifter by a turning amount necessary for changing over the establishment conditions of a plurality of change gear stages of gear trains.

Abstract: To provide a pump drive structure for a water-cooled internal combustion engine in which the number of revolving shafts arranged in parallel in an internal combustion engine is reduced and a power transmission mechanism is eliminated. Thus, the internal combustion engine is downsized. The pump drive structure of a water-cooled internal combustion engine is provided in which a balancer shaft is arranged in parallel with a crankshaft at a position where crank webs of the crankshaft and balancer weights are overlapped in the axial direction. An oil pump drive shaft of an oil pump is connected coaxially at one end of the balancer shaft, and a water pump drive shaft of a water pump is connected coaxially with the other end of the balancer shaft.

Abstract: A reverse inhibitor mechanism for a transmission of an all terrain vehicle, in which a shift drum is jounalled to a side wall opposite the transmission case so as to be rotatably supported thereon, and a reverse inhibitor arm is detachably engaged with the reverse inhibitor groove formed in the outer circumferential surface of the shift drum to regulate a reverse setting. A reverse inhibitor shaft having the reverse inhibitor arm supported at one end thereof is positioned within the transmission case. The other end of the reverse inhibitor shaft is rotatably journaled to one of the opposite side walls of the transmission case from the inside of the transmission case. A distal end of the reverse inhibitor arm which swings by the rotation of the reverse inhibitor shaft is brought into engagement with the reverse inhibitor groove during assembly of the reverse inhibitor mechanism.

Abstract: A lubricating device for an internal combustion engine includes an oil tank chamber defined by being separated from a crank chamber by a partition wall that is formed between a crankcase and a crankcase cover of the internal combustion engine. Oil pumped by a scavenge pump is supplied to a tank supply port which is open at an upper portion of the oil tank chamber to the oil tank chamber. The oil stored in the oil tank chamber is sucked from a feed suction port which is open at a lower portion of the oil tank chamber to be supplied to respective regions for lubrication of the internal combustion engine by a feed pump. An oil passage penetrating inside the oil tank chamber is formed below the tank supply port at an upper portion of the oil tank chamber.

Abstract: An oil pump unit for an internal combustion engine can reduce the number of component parts to configure a simplified pump case, reducing the size and weight thereof. In an oil pump unit has a case cover put on the outside of a crankcase via a spacer and an oil tank chamber formed by the inside surface of the case cover and the spacer. The spacer is formed inside an outer circumferential wall thereof with a division wall which partitions the oil tank chamber from a crank chamber and with one pump case half-body portion forming a half-body of a pump case of an oil pump. Another pump case half-body is joined to the pump case half-body portion to form the pump case. The pump case half-body portion is formed in a lower portion thereof with an oil suction port communicating with a bottom portion of the oil tank chamber.

Abstract: An output shaft of a power unit having a driven gear for supplying a power of an internal combustion engine via a transmission mechanism and for outputting the power to an outside of a unit case. Borne members are connected respectively at each end of a cylindrical member of the output shaft. The borne members are rotatably supported by the unit case via a pair of bearings. The driven gear is fitted to one of the borne members in a position adjacent to one of the bearings. As a result, the output shaft of the power unit can be manufactured by a compact manufacturing apparatus, and the output shaft can be reduced in weight while maintaining the strength.

Abstract: An oil filter mounting structure in an internal combustion engine in which the outside a crankcase in the direction of a crankshaft is covered by a case cover. A spacer is interposed between the crankcase and the case cover. The spacer is formed with a lubrication system. An oil filter is mounted to an oil filter mounting surface of the spacer which is flush with a mating surface with respect to the crankcase. A part of the crankcase to which the oil filter mounting surface of the spacer faces is formed with a recess opening on top to which the oil filter is mounted. The resulting configuration provides an oil filter mounting structure in which an oil filter is reliably protected from stones. Further, oil channels are shortened to achieve a compact light-weight internal combustion engine.

Abstract: A breather structure for internal combustion engine, the structure making a breather chamber smaller and thus making an internal combustion engine as a whole smaller. A breather chamber and a small chamber are formed. The breather chamber includes a first side face cover. The first side face cover is joined to a case to cover a first one of the right and left side faces of the case. Inside the first side face cover, an auxiliary apparatus chamber is formed. The auxiliary apparatus chamber houses a clutch mechanism connecting or disconnecting the power transmission route. Additionally, formed inside a housing are an external communication port communicating to the outside of the housing, and the small chamber communicating to a crank chamber and to the auxiliary apparatus chamber. Moreover, the auxiliary apparatus chamber communicates to the breather chamber.

Abstract: An engine for vehicle includes an oil hydraulic automatic transmission for changing the change gear ratio by control of an oil pressure. The oil pressure control unit of the transmission includes a plurality of control valves for controlling the oil pressure, and is mounted to an upper portion of a crankcase. A power transmission shaft interlockedly connected to a counter shaft and having an axis parallel to the counter shaft is disposed on the lower rear side of the counter shaft, and a drive bevel gear on the power transmission shaft and a driven bevel gear are meshed with each other on the rear side of the axis of the power transmission shaft. The resulting configuration eliminates the need for a special measure to protect the oil pressure control unit, and prevents interference of the driven bevel gear with the gear speed change mechanism.

Abstract: A starting clutch includes a clutch inner that is secured to and supported by a drive plate boss fitted to a crankshaft near the end thereof. A one-way clutch is fitted to the outer periphery of the cylindrical portion extending inwardly. A clutch outer forms an annular portion that covers the outer periphery of the drive plate. A hollow disk portion covers the inner surface and is rotatably supported by the crankshaft. The one-way clutch is clamped by the inner peripheral edge of the hollow disk portion of the clutch outer from the outer peripheral side in cooperation with the cylindrical portion of the drive plate boss, and the inner peripheral edge of the hollow disk portion of the clutch outer abuts against a flange portion of the drive plate boss extending along the inner surface of the drive plate in the centrifugal direction thereof.

Abstract: A water-cooled internal combustion engine configured so as to facilitate the change of the cooling system, thereby reducing costs. The crankcase of the water-cooled internal combustion engine is adapted to journal a crankshaft. The crankcase is covered by a crankcase cover from the axial outside. The crankcase is connected to the crankcase cover through an annular shaped spacer, and at least part of a water pump is formed integrally with the spacer.

Abstract: To advance the pivotally supporting point of a swing arm on a vehicle body frame, the distance in the forward and backward direction between a crankshaft and a countershaft of a transmission is decreased as much as possible thereby making the length of the swing arm great and sufficiently absorb upward and downward oscillation of a rear wheel to achieve stabilization of the vehicle body. A countershaft is disposed below a main shaft of the transmission while a shift drum is disposed rearwardly of the main shaft, and a driving sprocket wheel for driving a rear wheel is provided on the countershaft. An internal combustion engine is disposed on the vehicle body frame such that a rear portion of a transmission is positioned above a pivotally supporting point of a swing arm.

Abstract: The cartridge type transmission is a transmission configured to be detachable and attachable from/to the crankcase, the main shaft is arranged on the cut surface BF of the crankcase, and the change spindle and the shift fork shaft are pivotally supported in the upper crankcase, which is positioned on the upper side of the cut surface BF. The counter shaft is pivotally supported in the lower crankcase, which is positioned on the lower side of the cut surface BF.

Abstract: A multi-cylinder internal combustion engine draws oil from an oil reservoir with an oil pump, and supplies oil to individual areas of the engine, after passing the oil through an oil filter and an oil cooler. A filter case containing an element of the oil filter is mounted to a side surface of the engine to facilitate the removal and replacement of the case. The oil cooler and a balancer are each respectively mounted to a front central portion of the internal combustion engine to enable oil cooling by an air-cooling effect of a running airflow, and to balance weight in the left-right direction of the internal combustion engine. Oil discharged from the oil cooler is introduced to a substantially central portion of the main gallery, to achieve uniformity of oil pressure supplied to individual bearing portions and uniformity of cooling of the individual bearing portions.

Abstract: A cylinder head, for an internal combustion engine, enhances engine efficiency while ensuring favorable coolant flow. The cylinder head includes a main casting body 41 having a hollow water jacket formed therein, to allow coolant flow therethrough. The main casting body 41 includes a plurality of cylindrical plug hole walls 91 which have plug holes 90 formed therein inside a head-side water jacket 60. The cylinder head also includes partitions 100, formed inside the head-side water jacket 60, and these partitions connect the plug hole walls 91 together form a dividing wall, which divides the water jacket into an exhaust port section and an intake port section. Coolant entering the water jacket is divided into two substreams, which flow initially in substantially opposite directions, and which are reunited after flowing around opposite ends of the dividing wall.

Abstract: The cartridge type transmission is a transmission configured to be detachable and attachable from/to the crankcase, the main shaft is arranged on the cut surface BF of the crankcase, and the change spindle and the shift fork shaft are pivotally supported in the upper crankcase, which is positioned on the upper side of the cut surface BF. The counter shaft is pivotally supported in the lower crankcase, which is positioned on the lower side of the cut surface BF.

Abstract: To advance the pivotally supporting point of a swing arm on a vehicle body frame, the distance in the forward and backward direction between a crankshaft and a countershaft of a transmission is decreased as much as possible thereby making the length of the swing arm great and sufficiently absorb upward and downward oscillation of a rear wheel to achieve stabilization of the vehicle body.