Abstract: To miniaturize an engine, to concentrate heavy masses and to reduce friction loss of a balancer. An engine crankcase structure in which a crankcase is vertically partitioned into an upper case and a lower case, each journal supporter is formed in the upper case and in the lower case so that the rotational axis of a crankshaft is located on a partition face of the crankcase in parallel with a direction of the width of the body. The crankshaft is supported so that the crankshaft can be rotated. An oil filter is directly attached to the lower case. An oil cooler and a secondary balancer are arranged in the front of the lower case.

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.

Abstract: By blocking off a partial passage opening in a lubricating oil supply passage of a transmission gear mechanism by attaching a transmission holder, an operation to block off the passage opening is omitted. Supply of lubricating oil to a main shaft and a counter shaft of a transmission gear mechanism is carried out using branched passages from a main gallery, and the branched passage constitutes a lubricating oil supply passage to the main shaft while the branched passage constitutes a lubricating oil supply passage to the counter shaft. A partial passage opening of the branched passage is then blocked up at the time of attaching a transmission holder to the transmission case, and in this way a lubricating oil supply passage to the counter shaft is formed.

Abstract: A threaded fastener is configured to reduce stress experienced at a female threaded portion of a hole formed in an engine block, when the threaded fastener is inserted therein, and when an axial load is applied thereto. In a particular application, a crankshaft is supported between a top supporting wall of a crankcase and a bottom supporting wall of a main cap. The inventive bolt includes a hollowed-out male threaded portion, which fits into a hole in the top supporting wall. The male threaded portion includes an elastically deformable low-rigidity portion, in which a cylindrical hole is concentrically formed. The maximum allowable stress of the top supporting wall is less than that of the bolt, due to material considerations. The low-rigidity portion is placed overlapping the female threaded portion in the axial direction, and since it is elastically deformable, it helps alleviate the stress experienced by the female threaded portion.

Abstract: To facilitate attachment/detachment work of an oil filter in a vehicle engine without increasing an outer dimension thereof, and to provide a uniform a supply of engine oil into an engine body. An oil filter is attached onto a front portion of the engine body so as to be detachable in a vehicle body width direction from a side face of the engine body. An exhaust pipe on a side on which an oil filter is attached is displaced to a center side in the vehicle body width direction so as not to overlap the oil filter when viewed from a front of the engine body.

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 gear position detecting system includes structure which facilitates mounting of the system, and minimizes direct contact of other objects with the system. The outer circumferential surface of a shift drum, turned by operation of a change pedal, is provided with lead grooves. Shift forks, engaged with the lead grooves, are moved in the left-right direction by turning of the shift drum, whereby shift gears are changed over, and a speed change desired by the rider is performed. A detection pin of a neutral safety switch, which is one of gear position sensors, is pushed in by a detection cam of a cam surface provided at the outer circumferential surface of the shift drum in the speed change operation position, whereby a neutral position is detected.

Abstract: A piston cooling structure for a multicylinder engine having oil jets for ejecting oil toward pistons. The oil jets are mounted in each of a plurality of journal walls except one journal wall. The piston cooling structure is able to supply oil to a cylinder head in a position closer to a central region along the axis of the crankshaft while avoiding a complex oil passage shape. An oil passage for guiding oil to a cylinder head is defined in the one of the journal walls without an oil jet, and this one journal wall is disposed between a pair of adjacent cylinder bores. Oil jets are mounted in each of the other journal walls. A crankshaft of the engine is rotatably supported by the journal walls.

Abstract: A cylinder block of a multicylinder engine, having a cylinder main body in which multiple cylinder bores are provided in parallel in an axial direction of a crankshaft, and a crankcase having plural journal walls. The crankcase is integrally provided with the cylinder main body, in which a communication hole extending in parallel to the axial line of the crankshaft is provided in the cylinder main body and the crankcase while at least a part of which is opened in the inner peripheral surface of the cylinder bore. This permits the cylinder block to be downsized, increases freedom of positional setting of the communication hole, and reduces ventilation resistance of air flow through the communication hole. A cut-processed member is expanded further outward from a piston slide surface and is formed along a radial direction of cylinder bores, in inner surfaces of the cylinder bores in at least portions closer to a piston at an open edge of a communication hole.

Abstract: A piston cooling structure for a multicylinder engine having oil jets for ejecting oil toward pistons. The oil jets are mounted in each of a plurality of journal walls except one journal wall. The piston cooling structure is able to supply oil to a cylinder head in a position closer to a central region along the axis of the crankshaft while avoiding a complex oil passage shape. An oil passage for guiding oil to a cylinder head is defined in the one of the journal walls without an oil jet, and this one journal wall is disposed between a pair of adjacent cylinder bores. Oil jets are mounted in each of the other journal walls. A crankshaft of the engine is rotatably supported by the journal walls.

Abstract: To suitably keep the weight balance of an engine while reducing a radial dimension of the engine. A crank shaft and a transmission shaft are supported in casings and are disposed to be substantially parallel to each other. A rear balancer and a front balancer are disposed with the crank shaft placed therebetween. An AC generator is disposed at an end portion of the crank shaft on the left side with respect to a plane passing through a center of gravity of an engine and being perpendicular to the crank shaft. A clutch is disposed at an end portion of the transmission shaft on the right side with respect to the plane. The clutch is separated from the plane at a distance smaller than that between the AC generator and the plane, so that the weight balance of the engine is suitably maintained by disposing the rear balancer and the front balancer on the clutch side.

Abstract: A structure for blocking an oil supply hole of a kick idle gear bearing portion is provided in an internal combustion engine of a type wherein a kick starting mechanism is removably mounted for transmitting an input from a kick arm to a crank shaft by way of a kick idle gear rotatably supported by a counter shaft. When the kick starting mechanism is removed and a self stating mode is set, an oil supply hole of a bearing portion in the state that the kick idle gear of the counter shaft is removed is blocked by a blocking member having a slip preventive function. The blocking member includes an insertion portion inserted in the oil supply hole, and an abutment portion integrally formed with the insertion portion, which is abutted on the outer peripheral surface of the bearing portion.

Abstract: An arrangement of oil passages to a valve system can reduce the number of parts required thereby lowering the manufacturing cost. The oil passages to a valve system of an internal combustion engine are integrally formed with the cylinder block and a cylinder head. These oil passages are arranged along the outer surfaces on a side opposed to a cylinder liner and a combustion chamber relative to a valve system drive transmission.

Abstract: In a supercharged engine, a supercharger and a throttle body disposed midway in an intake passage are located away from an engine block. A blow-by gas passage constituting a PCV apparatus is connected between a portion of the intake passage located on the upstream side of a throttle valve and a crankcase. The blow-by gas passage returns the blow-by gas collected in the crankcase to the intake passage. A cooling water passage extending from the engine block is connected to a radiator. A water passage extending from the radiator is connected to the engine block via the throttle body, which water passage encloses the blow-by gas passage in an intermediate portion thereof.

Abstract: This invention is concerned with an improved system of dynamic balancing of the primary and secondary vibrations associated with combustion and inertial momentum effects, in particular, in single cylinder engines. By means of the primary and secondary balancing shafts, the invention achieves maximum balancing effects in small spaces, by combining the power transmission and dynamic balancing functions of the shafts; by mechanical arrangement of the primary and secondary balancing shafts in the vicinity of and parallel with the crank shaft; and by a judicious choice of the inter-shaft distances to permit placing the largest possible momentum balancing weights to the balancing sections.