Abstract: A vibration isolating structure for a power unit. The power unit includes an internal combustion engine equipped with transmissions. The vibration isolation structure includes torque dampers disposed between transmission gears of the transmission and a power transmission shaft supporting the transmission gears.

Abstract: A drum type-variable speed drive wherein a spring bearing member, which is restricted from moving in the axial direction of departing from a shift fork by a locking member fixed to a shift fork shaft, is pivotally supported by the shift fork shaft. A lost motion spring is interposed between the spring bearing member and the shift fork. Movement of the shift fork shaft in the axial direction caused by rotation of a shift drum presses the spring bearing member through the locking member, whereby the spring load of the lost motion spring acts on the shift fork.

Abstract: A shift drum structure for a drum-type transmission in which a shift fork moving on a shift fork shaft in an axial direction while guided by a guide groove in response to a turn of a shift drum, changes speeds by sliding a shifter member on a transmission driving shaft pivotally supporting a transmission gear, the shift drum. The shift drum includes a cylindrical drum main body and drum spindles projecting outward from drum end walls on the respective two sides of the drum main body, and the guide groove formed in an outer peripheral surface of the drum main body in a circumferential direction, wherein in the shift drum, a work groove is formed in the outer peripheral surface of the drum main body from one end surface to an opposite end surface of the drum main body, or to the guide groove near the opposite end surface.

Abstract: A drum type-variable speed drive wherein a spring bearing member, which is restricted from moving in the axial direction of departing from a shift fork by a locking member fixed to a shift fork shaft, is pivotally supported by the shift fork shaft. A lost motion spring is interposed between the spring bearing member and the shift fork. Movement of the shift fork shaft in the axial direction caused by rotation of a shift drum presses the spring bearing member through the locking member, whereby the spring load of the lost motion spring acts on the shift fork.

Abstract: A vibration isolating structure for a power unit. The power unit includes an internal combustion engine equipped with transmissions. The vibration isolation structure includes torque dampers disposed between transmission gears of the transmission and a power transmission shaft supporting the transmission gears.

Abstract: A shift drum structure for a drum-type transmission in which a shift fork moving on a shift fork shaft in an axial direction while guided by a guide groove in response to a turn of a shift drum, changes speeds by sliding a shifter member on a transmission driving shaft pivotally supporting a transmission gear, the shift drum. The shift drum includes a cylindrical drum main body and drum spindles projecting outward from drum end walls on the respective two sides of the drum main body, and the guide groove formed in an outer peripheral surface of the drum main body in a circumferential direction, wherein in the shift drum, a work groove is formed in the outer peripheral surface of the drum main body from one end surface to an opposite end surface of the drum main body, or to the guide groove near the opposite end surface.

Abstract: A transmission assembly includes a shift drum operable to rotate in first and second directions. The shift drum includes a common speed change position, where both a fastest forward gear and a reverse gear are capable of becoming engaged, in such a manner that a reverse stopper arm fits at a first end of a reverse cam groove formed on the shift drum. When the shift drum is rotated in the second rotation direction, opposite to the first direction, from a state where the reverse gear is engaged, the reverse stopper arm surmounts the outer periphery of the shift drum from the first end of the reverse cam groove, without requiring the application of an external force thereto, so as to become detached and to move towards a second end of the reverse cam groove.

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: 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: 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: 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: 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: 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: 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: 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 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: 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: 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: 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 transmission assembly includes a shift drum operable to rotate in first and second directions. The shift drum includes a common speed change position, where both a fastest forward gear and a reverse gear are capable of becoming engaged, in such a manner that a reverse stopper arm fits at a first end of a reverse cam groove formed on the shift drum. When the shift drum is rotated in the second rotation direction, opposite to the first direction, from a state where the reverse gear is engaged, the reverse stopper arm surmounts the outer periphery of the shift drum from the first end of the reverse cam groove, without requiring the application of an external force thereto, so as to become detached and to move towards a second end of the reverse cam groove.