Abstract: A motorcycle is provided in which a seat and a storage box are arranged so as to be vertically stacked on each other in a rear portion of a body frame, and a pivotally mounted powertrain unit is suspended from the body frame under the storage box. The powertrain unit extends in the fore-and-aft direction of the body frame, and the engine has a crank chamber and a lubricant oil chamber provided separately from each other. A lubrication-oil passage structure for the engine is provided between each of a pair of journal bearing portions of a crankcase. The crankcase has an enclosed crank chamber and a crankshaft which is freely rotatably supported by the journal bearing portions with plain bearings. The journal bearing portions are provided with protrusion bosses for resisting entry of lubricating oil into the crank chamber from outside of the crankcase.

Abstract: An engine cooling structure for a water cooled engine includes water pump and a thermostat. The water pump pumps coolant to a water jacket of the engine. The water pump and thermostat are provided on a cover member installed on an outside of a crankcase of the engine, and a coolant passage, which communicates with the water jacket through the water pump from the thermostat, is integrally formed in the cover member, so as to obtain arrangement of the cooling structure that is efficient in terms of space. The engine cooling structure increases the degree of freedom of layout around a cylinder head by keeping the projection amount on a side of the cylinder head small, simplifies the piping construction, and reduces the number of assembly steps.

Abstract: A motorcycle is provided in which a seat and a storage box are arranged so as to be vertically stacked on each other in a rear portion of a body frame, and a pivotally mounted powertrain unit is suspended from the body frame under the storage box. The powertrain unit extends in the fore-and-aft direction of the body frame, and the engine has a crank chamber and a lubricant oil chamber provided separately from each other. A lubrication-oil passage structure for the engine is provided between each of a pair of journal bearing portions of a crankcase. The crankcase has an enclosed crank chamber and a crankshaft which is freely rotatably supported by the journal bearing portions with plain bearings. The journal bearing portions are provided with protrusion bosses for resisting entry of lubricating oil into the crank chamber from outside of the crankcase.

Abstract: In a motorcycle power unit, a crank shaft (56) and a clutch shaft (57) disposed on the right side (in the figure) from a body center (127) and a cylinder head (129H) is disposed on the left side from the body center (127). Since the crank shaft, the clutch shaft and a transmission shaft are disposed on one of right and left sides with respect to the body center and the cylinder is disposed on the other side with respect to the body center, it becomes possible to make a favorable lateral balance of the power unit.

Abstract: A motorcycle (1) is disclosed wherein a crank shaft (56) is disposed in a lower portion of a power unit case (55), a clutch shaft (57) is disposed in parallel to and higher than the crank shaft (56), and a transmission shaft (58) and an electric motor shaft (59) are disposed in such a manner as to extend from one end of the clutch shaft (57) in a longitudinal (fore and aft) direction of the vehicular body. That is, the clutch shaft (57), transmission shaft (58), and electric motor shaft (59) are disposed in series and also in parallel to and higher than the crank shaft (56). Since the transmission shaft (58) and the electric motor shaft (59) are disposed in series in the longitudinal direction of a vehicular body, the direction of a force applied to the power unit case (55) becomes simple. This makes the designing of the power unit case easy.

Abstract: To provide a compact water-cooled four cycle engine suitable for a hybrid type power unit. The tension of a belt is increased by loosening bolts, turning an eccentric tube fitting, and moving a common pulley. After the tension of the belt is thus adjusted, the bolts are fastened. A water pump, which is supported by a shaft portion fitted in a guide groove and by the two bolts, are not moved except for the step of adjusting the tension of the belt 122. Since the tensioner serves as the pump pulley, it is possible to reduce the number of pulleys and hence to simplify the layout of the pulleys and reduce the number of parts. In accordance with another aspect of the present invention, a thermostat is mounted in a water jacket near an intake port of a cylinder head and is covered with an intake manifold. It is therefore unnecessary to provide a case and a lid for mounting the thermostat.

Abstract: To provide a power unit less affected by the length of the cylinder of an engine. A cam shaft drive mechanism is composed of a cam shaft drive pulley, a belt, a pair of cam shaft pulleys, and a tensioner disposed on the front surface of a power unit. Since the cylinder is disposed in the width direction of the vehicular body with its cylinder axis substantially in the horizontal direction (for example, a tilt angle .alpha. with respect to the ground is set at +10), the center of gravity of the vehicle is lowered and also the cylinder length can be set within the vehicular width. This increases the degree of design of the vehicle.

Abstract: A motorcycle engine having a cooling device is constructed as an OHC type multi-cylinder engine arranged on a vehicle frame with a plurality of cylinders being aligned perpendicularly to the longitudinal direction of the body frame, wherein a radiator provided with a forced cooling fan and a carburetor leading to engine intake ports are disposed forwardly and rearwardly of the engine, respectively, a timing transmission device for driving a valve-actuating cam shaft of the engine is arranged so as to deviate to one side from the center of the cylinder block in the alignment direction of said cylinders, the timing transmission device and the radiator fan being arranged side-by-side in the longitudinal direction of the frame, a plurality of bearing holders are provided separately on the engine cylinder head correspondingly to the cylinders to rotatably support a valve-actuating cam shaft extending in the alignment direction of the cylinders, and a head cover covering the cylinder head provides wind guiding pass