JP2006103497A - Power unit for motorcycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a structure compact while securely supporting a kick starter shaft, to decrease the weight of a transmission case cover, to save a cost, and to improve the freedom of shape. <P>SOLUTION: A transmission case 47 is backwardly extended from one side portion of a crank case 41 of an engine 37. A rear wheel 17 is journaled at a rear portion of the transmission case 47, and a belt type transmission 48 is stored inside, thereby structuring a transmission unit 38. The transmission case 47 is composed of a transmission case main body 45 integrated with the crank case 41, and supporting a driving shaft (a crank shaft 52), a driven shaft 56, and a rear wheel shaft 58 of the belt type transmission 48; and the transmission case cover blocking an opening on the outside in a vehicular width direction of the transmission case main body 45. A kick starter shaft 141 extending in the vehicular direction is suspended at a middle portion of the transmission case 47, and the kick starter shaft 141 is pivoted by the transmission case main body 45 and a kick starter shaft supporting member 146 detachably provided on the transmission case main body 45. In a side view on the vehicle side, the kick starter shaft supporting member 146 is put side by side behind a cooling air intake port 178 provided at a front end portion of the transmission case 47. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power unit of a motorcycle in which an engine and a transmission unit are integrated and a rear wheel is directly supported at a rear portion.

  As shown in Patent Document 1, many of the scooter type motorcycles include a power unit in which an engine and a transmission unit are integrated and a rear wheel is directly supported at a rear portion. The transmission unit houses a belt-type transmission in a transmission case extending rearward from the crankcase of the engine and incorporates a kick starter mechanism for starting the engine and a belt cooling device for cooling the belt-type transmission.

  Generally, a transmission case is composed of a transmission case main body that is provided integrally with the crankcase, and a transmission case cover that closes an opening on the outer side in the vehicle width direction of the transmission case main body. It is pivotally supported across the case cover.

The belt cooling device includes a cooling air suction fan provided integrally with a drive pulley of the belt-type transmission, and a cooling opening provided at a front portion of the transmission case cover so as to be positioned in the vicinity of the cooling air suction fan. And an air inlet.
Patent Abstract No. 2640654

  However, as described above, since the kick starter shaft is conventionally supported by straddling the transmission case body and the transmission case cover, the transmission case cover has sufficient strength against the strong kick force applied to the kick starter shaft. Therefore, the transmission case cover has to be made of metal similar to that of the transmission case main body. In other words, it can be said that the shift case cover was made of metal only to obtain the support strength of the kick starter shaft, and therefore, a great increase in weight and manufacturing cost were forced.

  In addition, the cooling air intake fan and the cooling air intake opening that constitute the belt cooling device are both arranged at the front part of the speed change case, which causes the width of the front part of the speed change case to be widened. Since the motorcycle rider is likely to interfere with the shin of the foot when the foot is on the ground, it is necessary to reduce the lateral width as much as possible.

  The present invention has been made to solve the above-mentioned problems, and while being able to firmly support the kick starter shaft, the structure is compact, and the weight of the transmission case cover is reduced, the cost is reduced, and the degree of freedom in shape is improved. Another object of the present invention is to provide a power unit for a motorcycle that can be made compact and that can reduce the size of the front portion of the transmission case.

  In order to achieve the above object, a power unit for a motorcycle according to the present invention includes a single-cylinder cylinder assembly extending substantially horizontally forward on a front surface of a crankcase including a crankshaft extending in a vehicle width direction, and constitutes an engine. The transmission case is extended rearward from one side of the crankcase, the rear wheel is pivotally supported at the rear and a belt-type transmission is housed therein to form a transmission unit. The transmission case is integrated with the crankcase. And a transmission case body that supports the drive shaft, the driven shaft, and the rear wheel shaft of the belt-type transmission, and a transmission case cover that closes the opening in the vehicle width direction of the transmission case body. A kick starter shaft extending in the vehicle width direction is installed in the middle of the transmission case, and this kick starter shaft is connected to the transmission case body. And rotatably supported by the kick starter shaft support member provided detachably on the case main body.

  In the power unit of the motorcycle according to the present invention, the kick starter shaft support member is detachably fixed to the transmission case body by three or more support portions surrounding the kick starter shaft, and the kick starter shaft is rotated. A kick transmission mechanism for transmitting the movement to the crankshaft is supported by the kickstarter shaft support member.

  Furthermore, the power unit of the motorcycle according to the present invention has a predetermined length at three or more support portions of the kick starter shaft support member so that an operating space is formed between the transmission case main body and the kick starter shaft support member. The kick transmission mechanism is housed in this working space, and the kick starter shaft support member is covered with the drive shaft and drive pulley of the belt-type transmission, and the kick starter shaft support member is supported by three or more support portions. Placed above and below the pulley.

  The motorcycle power unit according to the present invention includes a stepped portion recessed inward in the vehicle width direction at a front end portion of the transmission case cover, and a cooling air suction port of the belt-type transmission is formed in the stepped portion. The cooling air suction port is overlapped with the front edge of the drive pulley of the belt-type transmission in a vehicle side view, and a cover member that covers the cooling air suction port is detachably provided on the stepped portion. The kick starter shaft support member is opposed to the transmission case cover.

  Further, the power unit of the motorcycle according to the present invention includes an opening formed in the transmission case cover, with an elastic member interposed between the transmission case body and the transmission case cover so that the transmission case cover floats and supports the transmission case body. The kick starter shaft was extended from the opening, and a gap was provided between the opening and the kick starter shaft.

  According to the motorcycle power unit of the present invention, the kick starter shaft is firmly supported by the speed change case body and the kick starter shaft support member that is detachably provided on the speed change case body, and the speed change case cover is provided at the time of kick start. Since no kick load is applied, the transmission case cover can be formed of a non-metallic material, and the transmission case cover can be reduced in weight, cost can be reduced, and the shape flexibility can be improved.

  In addition, a cooling air suction port is formed in a step provided at the front end of the transmission case cover, and a cover member covering the cooling air suction port is provided in the step so that the cover member sandwiches the transmission case cover in a side view of the vehicle. Thus, since the kick starter shaft support member is opposed to the above, it is possible to achieve downsizing of the front portion of the transmission case, particularly reduction in width.

  The following is an embodiment of the present invention.

  FIG. 1 is a left side perspective view showing a scooter type motorcycle to which a power unit according to the present invention is applied.

  The body frame 2 of the motorcycle 1 is made of steel pipe, and a down pipe 4 extends rearward and downward from a head pipe 3 located at the frontal portion, and a pair of left and right rear pipes 5 extends rearward and obliquely upward from the vicinity of the rear end thereof. A step frame 6 is formed at a portion where the pipe 4 enters the lower part, and an engine bracket 7 is provided in the vicinity of the joint between the down pipe 4 and the rear pipe 5.

  A front fork 10 that supports a front wheel 9 is pivotally supported on the head pipe 3 together with a handle bar 11, a headlamp 12, a front fender 13, and the like, while being pivotally supported by the engine bracket 7 via a link 15. The rear wheel 17 is supported on the rear part of the power unit 16, and the shock absorber 18 is connected between the rear part of the power unit 16 and the rear part of the rear pipe 5.

  The power unit 16 swings up and down around a pivot shaft 19 installed at the rear end of the link 15 together with the rear wheel 17 to act as a swing arm of the rear wheel 17, and the power unit 16 and the rear wheel 17 are swung by a shock absorber 18. Buffered and restored. An air intake device (discharge pump) 21 is installed at the front upper part of the power unit 16, and an air cleaner 22 is installed at the rear upper part.

  A bottomed box-shaped container-like article storage box 24 that opens upward is installed above the rear pipe 5, and a seating seat 25 is placed so as to close the opening. The seating seat 25 can be opened and closed by lifting the rear end about the hinge portion 26 at the front end, so that articles can be taken in and out of the article storage box 24.

  A fuel tank 27 is installed behind the article storage box 24, and a refueling portion 28 passes through a tray portion 29 extending rearward from the upper edge of the article storage box 24 and faces upward. The fuel tank 27 has a shape that wraps around right after the article storage box 24.

  The front and rear portions of the vehicle body frame 2 are covered with a resin front frame cover 31 and a rear frame cover 32, respectively, to adjust the vehicle body appearance. A tail lamp 33 is provided at the rear end of the rear frame cover 32, and A rear fender 34 is provided above the wheel 17. A resin step board 35 is formed on the top of the step frame 6. The front frame cover 31, the rear frame cover 32, and the step board 35 are continuously connected.

  2 is a left side view of the power unit 16, FIG. 3 is a plan view of the power unit 16, and FIG. 4 is a cross-sectional view of the power unit 16 taken along line IV-IV in FIG. This power unit 16 has a general layout for a scooter type motorcycle in which a four-cycle engine 37 and a transmission unit 38 are integrated.

  The four-cycle engine 37 is a forced air-cooling type, and a single-cylinder cylinder assembly 42 is installed on the front surface of the crankcase 41 so as to be inclined forward substantially horizontally. As shown in FIG. 4, the crankcase 41 is a left-right split type in which the left case half 43 and the right case half 44 are combined. The left case half 43 is integrally provided with a transmission case main body 45 extending rearward. The left side opening of the transmission case body 45 is closed by a transmission case cover 46 to form a transmission case 47, and the transmission unit 38 is constituted by the transmission case 47, the belt-type transmission 48 and the deceleration transmission mechanism 49 housed therein. It is configured.

  A crankshaft 52 extending in the vehicle width direction is supported inside the crankcase 41, and both ends of the crankshaft protrude to the left and right of the crankcase 41, and the left end of the crankshaft 52 extends into the transmission case 47 so as to be belt-type transmission 48. Also serves as the drive axis.

  On the other hand, a driven shaft 56, an intermediate shaft 57, and a rear wheel shaft 58 are supported in order from the front at the rear portion of the transmission case 47, and the rear wheel shaft 58 protrudes from the right side surface of the transmission case 47 so that the rear wheel 17 rotates integrally therewith. It is attached. The crankshaft 52, the driven shaft 56, the intermediate shaft 57, and the rear wheel shaft 58 are supported by the transmission case body 45 and are not supported by the transmission case cover 46.

  Inside the speed change case 47, a drive pulley 61 is mounted on the crankshaft 52, and a driven pulley 62 is mounted on the driven shaft 56, and a V-belt 63 is stretched between the pulleys 61 and 62, and on the left side of the driven pulley 62. A centrifugal clutch 64 is provided. The pulleys 61 and 62, the V belt 63, and the centrifugal clutch 64 constitute a belt type transmission 48.

  A primary drive gear 66 is provided near the right end of the driven shaft 56, a primary driven gear 67 and a secondary drive gear 68 are provided on the intermediate shaft, and a secondary driven gear 69 is provided on the rear wheel shaft 58. .. -69 are separated in a liquid-tight manner by a mission cover 70 mounted on the rear portion of the transmission case main body 45 and immersed in oil to constitute a deceleration transmission mechanism 49.

  The rotation of the crankshaft 52 is transmitted to the driven shaft 56 through the drive pulley 61, the V belt 63, the driven pulley 62, and the centrifugal clutch 64, and the rotation of the driven shaft 56 is decelerated in two stages by the speed reduction mission mechanism 49. And transmitted to the rear wheel 17. The effective diameter of the drive pulley 61 is increased by the action of the internal weight roller 71 as the centrifugal force increases. On the contrary, the effective diameter of the driven pulley 62 is reduced, so that the rotation of the crankshaft 52 is automatically changed steplessly ( And is transmitted to the driven shaft 56.

  On the other hand, the cylinder assembly 42 is assembled from a cylinder block 85, a cylinder head 86, and a head cover 87. A piston 89 inserted into a cylinder bore 88 inside the cylinder block 85 is connected to a crank pin 91 of the crankshaft 52 by a connecting rod 90. The reciprocating motion of the piston 89 in the cylinder bore 88 is converted into the rotational motion of the crankshaft 52 and becomes the output of the 4-cycle engine 37.

  A combustion chamber 93 that is aligned with the cylinder bore 88 is formed in the cylinder head 86 and a spark plug 94 is attached from the outside. A cam shaft 95 is supported in the vehicle width direction inside the cylinder head 86, and is attached to the crank shaft 52. A cam chain 98 is wound between a cam drive sprocket 96 provided and a cam driven sprocket 97 provided on the cam shaft 95.

  The rotation of the crankshaft 52 is decelerated to 1/2 and transmitted to the camshaft 95. The intake cam 99 and the exhaust cam 100 formed on the camshaft 95 are connected to an intake valve and an exhaust valve (not shown) via a rocker arm (not shown). ) At a predetermined timing. The cam chain 98 is accommodated in a cam chain chamber 101 provided on, for example, the right side surface of the cylinder assembly 42 (85, 86, 87).

  A gear cover member 104 is liquid-tightly mounted on the right side surface of the crankcase 41 (right case half 44), and an auxiliary machine drive gear chamber 105 is defined between the crankcase 41 and the crankshaft 52. The cam drive sprocket 96 and an oil pump drive gear 107 located on the outer side (right side) in the axial direction are accommodated.

  The gear cover member 104 is formed with a recess 127 that is recessed toward the auxiliary machine drive gear chamber 105, and a generator 128 that is rotationally driven by the crankshaft 52 is installed in the recess 127. The stator 129 of the generator 128 is fastened and fixed in the recess 127 with bolts, the right end portion of the crankshaft 52 passes through the center of the recess 127, and the rotor 132 of the generator 128 is rotatably integrated with the right end portion of the crankshaft 52. Yes. Then, the rotation of the crankshaft 52 causes the rotor 132 to go around the stator 129 to generate power.

  An engine cooling fan 135 is fixed to the rotor 132 of the generator 128, and the cylinder assembly 42 and the right side of the crankcase 41 are covered with a resin cooling cowling 136. The cooling cowling 136 is formed with a cooling air inlet 137 that opens to the right side of the engine cooling fan 135 and a cooling air discharge port that is not shown that opens below the cylinder assembly 42. When the cooling fan 135 rotates together with the rotation of the crankshaft 52, the outside air is sucked as cooling air from the cooling air suction port 137, and this cooling air is forced to cool the cylinder assembly 42 and then discharged from the cooling air discharge port. The cycle engine 37 is forcibly air-cooled.

  By the way, a kick starter shaft 141 along the vehicle width direction is pivotally supported at an intermediate portion of the transmission case 47, and a kick starter lever 142 is provided at an outer end (left end) of the kick case starter shaft 141. A starter mechanism 143 is provided. Note that a member 144 shown in FIG. 3 is a starter motor.

  As shown in enlarged views in FIGS. 5 and 6, a kick starter shaft support member 146 is detachably provided on the left side surface of the front portion of the transmission case body 45, and is provided on the kick starter shaft support member 146. A kick starter shaft 141 is rotatably supported by a bearing hole 147 and a bearing boss 148 provided in the transmission case main body 45.

  The kick starter shaft 141 extends leftward from an opening 151 formed in the transmission case cover 46, but a gap 152 is provided between the opening 151 and the kick starter shaft 141, and the kick starter shaft 141 is provided. Does not touch the shift case cover 46 directly. A dustproof and waterproof sealing member may be interposed in the gap 152.

  As shown in FIGS. 7 to 11, the kick starter shaft support member 146 includes a substantially plate-like support body 155 and three support portions 156, 157, and 158 that support the support body 155. The support body 155 is shaped so as to cover the drive shaft (crankshaft 52) of the belt-type transmission 48 and the rear half of the drive pulley 61, and the support portions 156 to 158 are arranged so as to surround the periphery of the kick starter shaft 141. Yes. Of these, the two support portions 156 and 157 are positioned above and below the drive pulley 61, and the remaining one support portion 158 is positioned behind the kick starter shaft 141 (see FIG. 6). Note that the support portions 156 to 158 may have three or more points.

  Each of the support portions 156 to 158 is fastened and fixed to fastening bosses 160 formed on the transmission case main body 45 by bolts. Of these, the support portion 158 located behind the kick starter shaft 141 is fastened to the transmission case body 45 by bolts 161 that fix the transmission case cover 46 to the transmission case body 45 (see FIGS. 4 and 5). A positioning knock pin 162 is interposed between the support portions 156 to 158 and the fastening bosses 160.

  Each support portion 156 to 158 of the kick starter shaft support member 146 is given a predetermined length (several centimeters), whereby the running lines of the transmission case main body 45 and the belt 63 and the kick starter shaft support member 146 (support main body) are provided. 155), a working space 165 is formed, and the above-described kick transmission mechanism 143 is accommodated in the working space 165.

  The kick transmission mechanism 143 is a known mechanism that transmits the rotation of the kick starter shaft 141 to the crankshaft 52, and is supported by the kick starter shaft support member 146 itself. The kick transmission mechanism 143 includes a return spring 167 that urges the kick starter shaft 141 in the backward direction, a fan-shaped starter drive gear 168 that is provided integrally with the kick starter shaft 141, a starter driven shaft 169, a starter driven gear 170, A starter clutch 171 and the like are provided.

  The support body 155 of the kick starter shaft support member 146 has a bearing hole 173 positioned in front of the bearing hole 147 for the kick starter shaft 141. The bearing hole 173 is located on the same axis as the crankshaft 52 and is a starter driven shaft. 169, a starter driven gear 170 is rotatably supported on the starter driven shaft 169, and a starter clutch 171 is provided between the starter driven gear 170 and the crankshaft 52.

  When the kick starter lever 142 is stepped down, the kick starter shaft 141 and the starter drive gear 168 rotate backward, and the starter drive gear 168 engages with the starter driven gear 170 to cause the starter driven gear 170 to rotate forward. As a result, the starter clutch 171 is clutch-coupled to rotate the crankshaft 52 forward, and the four-cycle engine 37 is started. After the start, the rotation of the crankshaft 52 becomes faster than the rotation of the starter driven gear 170, so that the clutch engagement of the starter clutch 171 is released, and the kick starter lever 142 is returned to the initial position by the urging force of the return spring 167.

  Since the kick starter shaft 141 is firmly supported by the transmission case main body 45 and the kick starter shaft support member 146, the kick starter shaft 141 is not bent with respect to a strong kick force, and a reliable startability is obtained. be able to.

  On the other hand, a step portion 177 having a substantially crescent shape that is recessed inward in the vehicle width direction is provided at the front end portion of the speed change case cover 46, and a cooling air intake port of the belt-type transmission 48 is provided on the inner side surface of the step portion 177. 178 is formed, and a duct half body 179 that opens downward is formed at the front lower part thereof. The cooling air inlet 178 overlaps the front half of the drive pulley 61 of the belt-type transmission 48 in a side view of the vehicle.

  A resin cover member 181 that covers the cooling air suction port 178 is detachably provided on the step 177 of the transmission case cover 46 with a screw 182. The cover member 181 is similar in shape to the crescent shape of the stepped portion 177 in a side view, and is formed with a duct half body 184 that overlaps the duct half body 179, and the two duct half bodies 179, 184 are combined and the inhalation opened downward A duct is constructed. For example, a sponge-like air cleaner element 186 is installed on the downstream side of the duct half body 184 of the cover member 181.

  As shown in FIG. 5, the cover member 181 faces the kick starter shaft support member 146 with the transmission case cover 46 (the rear surface of the stepped portion 177) interposed therebetween, and the cover member 181 and the kick starter shaft support member 146 are close to each other. The cover member 181 and the duct half body 184 do not protrude beyond the left side surface of the transmission case cover 46 in a plan view (see FIG. 3).

  On the other hand, a cooling air suction fan 190 is provided integrally with the left side surface of the drive pulley 61, and a cooling air discharge port 191 (see FIG. 2) that opens downward is provided at the rear portion of the transmission case cover 46.

  When the four-cycle engine 37 is operated, the cooling air suction fan 190 is rotated together with the drive pulley 61, and outside air is sucked from the suction ducts (the duct half bodies 179 and 184). The sucked outside air is filtered by the air cleaner element 186 inside the cover member 181 and then introduced into the transmission case 47 as cooling air from the cooling air suction port 178. The inside of the transmission case 47 flows from the front part to the rear part and flows through the belt type. After the transmission 48 is cooled, it is discharged to the outside from the cooling air discharge port 191.

  As shown in FIG. 5, a sleeve-like spacer 195 is provided between the head 161 of the bolt 161 that fixes the rear support portion 158 of the kick starter shaft support member 146 to the fastening boss 160 of the transmission case main body 45 and the support portion 158. A transmission case cover 46 is fitted around a grommet 196 made of an elastic material such as rubber or soft resin, which is mounted around the spacer 195. A similar structure is adopted in other bolt fastening portions of the transmission case cover 46, and a packing 198 made of an elastic material is fitted to the outer peripheral edge of the transmission case cover 46, and elastic such as the grommet 196 and the packing 198. The entire transmission case cover 46 is floatingly supported by the transmission case body 45 by the elasticity of the members.

  In the power unit 16 configured as described above, since the kick starter shaft 141 is pivotally supported by the transmission case main body 45 and the kick starter shaft support member 146, the kick starter shaft 141 is firmly supported and at the same time the transmission case cover 46 is provided. Thus, the shift case cover 46 can be made of a non-metallic material such as a resin, so that the shift case cover 46 can be significantly reduced in weight, cost, and shape flexibility. Etc. can be achieved. In addition, since the transmission case cover 46 can be brought close to the cooling air suction fan 190 of the drive pulley 61, the width dimension of the transmission case 47 can be made compact.

  The kick starter shaft support member 146 is detachably fixed to the transmission case main body 45 by three or more support portions 156 to 158 surrounding the kick starter shaft 141, and the kick transmission mechanism 143 is attached to the kick starter shaft support member 146. Since it is supported, the kick transmission mechanism 143 can be removed while being firmly supported with respect to the transmission case main body 45, so that the maintainability of the kick transmission mechanism 143 can be remarkably improved.

  Further, a predetermined length is given to the support portions 156 to 158 of the kick starter shaft support member 146 to form a working space 165 between the transmission case main body 45 and the kick starter shaft support member 146, and the working space 165 Since the kick transmission mechanism 143 is accommodated, the kick starter shaft support member 146 can be provided in a compact manner without obstructing the flow of the cooling air flowing inside the speed change case 47 or interfering with the running path of the belt 63.

  Further, the kick starter shaft support member 146 (support body 155) covers the crankshaft 52 and the drive pulley 61, and two support portions 156 and 157 are arranged above and below the drive pulley 61, and the one support portion 158 is provided. Since the kick starter shaft 141 is disposed at the rear portion, the kick starter shaft 141 can be supported with higher rigidity by increasing the fixing strength of the kick starter shaft support member 146.

  Further, a cooling air suction port 178 is formed in a step portion 177 provided at the front end portion of the speed change case cover 46, and a cover member 181 that covers the cooling air suction port 178 is detachably provided on the step portion 177 so as to be viewed from the side of the vehicle. Since the cover member 181 is opposed to the kick starter shaft support member 146 from the front, the front portion of the transmission case 47 can be made compact, particularly the width dimension can be reduced, and the rider of the motorcycle 1 can attach his / her foot to the ground. Therefore, it is possible to prevent the shin of the foot from interfering with the front portion of the speed change case 47, and to greatly improve the footing.

  Since the transmission case cover 46 is completely supported by the elastic members such as the grommet 196 and the packing 198 so as to float, the transmission case cover 46 is prevented from being stressed. This can further contribute to the weight reduction and shape simplification of the cover 46.

1 is a left side perspective view showing a scooter type motorcycle to which a power unit according to the present invention is applied. FIG. The left view of a power unit. The top view of a power unit. The figure which shows one Embodiment of this invention by the cross section of the power unit which follows the IV-IV line of FIG. The V section enlarged view of FIG. The left view which expanded the front part of the speed change case. The left view of a kick starter shaft support member. FIG. 8 is a cross-sectional view of the kick starter shaft support member taken along line VIII-VIII in FIG. 7. The right view of a kick starter shaft support member. The rear view of a kick starter shaft support member. The front view of a kick starter shaft support member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motorcycle 16 Power unit 17 Rear wheel 37 Four-cycle engine 38 Transmission unit 41 Crankcase 42 Cylinder assembly 45 Transmission case main body 46 Transmission case cover 47 Transmission case 48 Belt-type transmission 52 Crankshaft 56 which is a drive shaft of a belt-type transmission Driven shaft 58 Rear wheel shaft 61 Drive pulley 141 Kick starter shaft 143 Kick transmission mechanism 146 Kick starter shaft support member 151 Opening portion 152 Clearance 155 Support body 156, 157, 158 Support portion 165 Drive shaft 177 of the operating space belt type transmission 178 Cooling air inlet 181 Cover member 196 Grommet 198 as elastic member Packing as elastic member

Claims (5)

A single-cylinder cylinder assembly extending substantially horizontally forward is provided on the front surface of the crankcase containing the crankshaft along the vehicle width direction to form an engine. After that, the shift case is extended from one side of the crankcase to the rear, and then A rear wheel is pivotally supported on the part and a belt-type transmission is housed inside to form a transmission unit. The transmission case is provided integrally with the crankcase, and the drive shaft, the driven shaft, and the rear of the belt-type transmission are provided. A transmission case body that supports the wheel shaft and a transmission case cover that closes the opening of the transmission case body on the outer side in the vehicle width direction, and a kick starter shaft extending in the vehicle width direction is installed in the middle portion of the transmission case. The kick starter shaft is composed of a transmission case body and a kick starter shaft support member that is detachably provided on the transmission case body. Power unit for a motorcycle, characterized in that the rolling pivotally supported. The kick starter shaft support member is detachably fixed to the transmission case main body by three or more support portions surrounding the kick starter shaft, and the kick transmission mechanism for transmitting the rotation of the kick starter shaft to the crank shaft is kicked. The motorcycle power unit according to claim 1, wherein the power unit is supported by a starter shaft support member. A predetermined length is given to three or more support portions of the kick starter shaft support member so that an operation space is formed between the transmission case body and the kick starter shaft support member, and the kick transmission mechanism is provided in the operation space. 3. The housing according to claim 2, wherein the kick starter shaft support member covers the drive shaft and the drive pulley of the belt-type transmission, and three or more support portions of the kick starter shaft support member are arranged above and below the drive pulley. Motorcycle power unit. A step portion recessed inward in the vehicle width direction is provided at a front end portion of the transmission case cover, and a cooling air suction port of the belt-type transmission is formed at the step portion. A kick-starter shaft support member that overlaps the front edge of the drive pulley of the apparatus and that covers the cooling air suction port is detachably provided on the stepped portion, and the cover member sandwiches the speed change case cover in a side view of the vehicle. The motorcycle power unit according to any one of claims 1 to 3, wherein the power unit is opposed to the motorcycle. An elastic member is interposed between the transmission case body and the transmission case cover so that the transmission case cover floats and supports the transmission case body, the kick starter shaft extends from an opening formed in the transmission case cover, and The motorcycle power unit according to claim 1, wherein a gap is provided between the opening and the kick starter shaft.

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