Abstract:
A method of assembling an outboard engine is disclosed. The outboard engine has first and second driveshafts, each having a helical gear on a first end and a driving gear on a second end. A driven shaft has a driven gear. The method comprises: rotating the driven shaft; measuring an axial displacement of one of the first and second helical gears with respect to the engine casing; selecting a shim based at least in part on the measurement of the relative axial displacement; and placing the shim on the one of the first and second driveshafts at a position axially below the helical gear. A method of assembling a marine outboard engine comprising moving a height adjustment member from a first position to a second position based on the relative axial displacement is also disclosed. An outboard engine with first and second helical gears at different heights is also disclosed.

Description:
CROSS-REFERENCE 
     The present application is a divisional of U.S. patent application Ser. No. 11/963,080, filed Dec. 21, 2007 now U.S. Pat. No. 8,276,274, the entirety of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method of assembling a marine outboard engine. 
     BACKGROUND OF THE INVENTION 
     Many boats and other watercraft are driven by one or more outboard engines. Marine outboard engines have an engine, such as an internal combustion engine, that drives a vertically oriented driveshaft. The driveshaft is coupled to a driving gear that drives a driven gear mounted on a horizontally oriented propeller shaft that, in turn, drives a propeller to propel the boat forward. 
     In some applications, such as boat racing, it is desired to use a high-powered engine to provide a large amount of horsepower and torque for driving the propeller. In high-powered applications, all of the intermediate components between the engine and the propeller, such as the driveshaft, propeller shaft and the driving and driven gears therebetween, must be made correspondingly larger to reliably transmit the power, resulting in increased size and weight. In particular, the greater power requires a larger driven gear on the propeller shaft, which in turn may require a larger gear case housing. A larger gear case housing creates additional drag when the gear case housing is submerged in the body of water while the engine is being used, with an attendant decrease in performance and efficiency. In addition, because higher-powered engines require larger gear case housings than lower-powered engines, an increased number of parts must be designed, manufactured and kept in inventory and an attendant increase in manufacturing cost. 
     One alternative method of delivering a large amount of power to the propeller shaft is to provide two smaller driveshafts driving a single driven gear on the propeller shaft. In this arrangement, each driveshaft theoretically delivers half of the power output from the engine, and as a result each driveshaft can be smaller in size, and the driving and driven gears can be made correspondingly smaller, resulting in a lighter and more compact arrangement. 
     However, the arrangement having two driveshafts has drawbacks. The gears on the driveshafts and the propeller shaft generally do not mesh perfectly, due to manufacturing tolerances in the machining of the gears and difficulties in obtaining proper timing between the driving and driven gears during assembly of the engine. As a result, the power from the engine is unevenly distributed between the two driveshafts, resulting in increased and uneven wearing of the gears and the risk of applying more power to one of the driveshafts and its corresponding driving gear than they are designed to support. 
     One way of remedying these drawbacks is to manually attempt to mesh the teeth of the gears in numerous different arrangements, until one arrangement is found that satisfactorily balances the load between the two driveshafts. This procedure is time-consuming, resulting in increased manufacturing cost, and does not necessarily result in a complete balancing of the load. 
     Therefore, there is a need for a method of assembling a marine outboard engine to provide improved load balancing between the two driveshafts. 
     There is also a need for a marine outboard engine having improved load balancing between the two driveshafts. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to ameliorate at least some of the inconveniences present in the prior art. 
     It is a further object of the present invention to provide a method of assembling a marine outboard engine to provide improved load balancing between the two driveshafts. 
     It is a further object of the present invention to provide a marine outboard engine having improved load balancing between the two driveshafts. 
     In one aspect, the invention provides a method of assembling a marine outboard engine having an engine casing. A first driveshaft has a first end and a second end. The first end has a first helical gear disposed thereon. The second end has a first driving gear disposed thereon. A second driveshaft has a first end and a second end. The first end has a second helical gear disposed thereon. The second end has a second driving gear disposed thereon. A driven shaft has at least one driven gear disposed thereon. The method comprises: placing the first driveshaft in the engine casing such that the first helical gear is free to move in an axial direction relative to the engine casing; placing the driven shaft in the engine casing such that one of the at least one driven gear meshes with the first driving gear; placing the second driveshaft in the engine casing such that: the second driving gear meshes with one of the at least one driven gear, the first helical gear meshes with the second helical gear, and the second helical gear is free to move in an axial direction relative to the engine casing; rotating the driven shaft; measuring an axial displacement of one of the first and second helical gears with respect to the engine casing as a result of the rotation of the driven shaft; selecting a shim based at least in part on the measurement of the relative axial displacement; and placing the shim on the one of the first and second driveshafts at a position axially below the helical gear disposed on the one of the first and second driveshafts. 
     In a further aspect, the method comprises measuring the relative axial displacement includes placing a position indicator on at least one of the first and second helical gears. 
     In a further aspect, the method comprises fixing the first and second helical gears in position after placing the shim, such that axial movement of the first and second helical gears in an axial direction is substantially prevented after placing the shim. 
     In a further aspect, the at least one driven gear is a single driven gear. Placing the driven shaft in the engine casing such that one of the at least one driven gear meshes with the first driving gear comprises placing the driven shaft in the engine casing such that the driven gear meshes with the first driving gear. Placing the second driveshaft in the engine casing such that the second driving gear meshes with one of the at least one driven gear comprises placing the second driveshaft in the engine casing such that the second driving gear meshes with the driven gear. 
     In a further aspect, the at least one driven gear comprises first and second driven gears. Placing the driven shaft in the engine casing such that one of the at least one driven gear meshes with the first driving gear comprises placing the driven shaft in the engine casing such that the first driven gear meshes with the first driving gear. Placing the second driveshaft in the engine casing such that the second driving gear meshes with one of the at least one driven gear comprises placing the second driveshaft in the engine casing such that the second driving gear meshes with the second driven gear. 
     In an additional aspect, a marine outboard engine comprises an engine casing. A generally vertically oriented first driveshaft has a first end and a second end. The first end has a first helical gear disposed thereon. The second end has a first driving gear disposed thereon. A generally vertically oriented second driveshaft has a first end and a second end. The first end has a second helical gear disposed thereon. The second end has a second driving gear disposed thereon. A driven shaft has at least one driven gear disposed thereon. The at least one driven gear engages at least one of the first and second driving gears. At least one height adjustment member is disposed on at least one of the first driveshaft and the second driveshaft such that the first helical gear and the second helical gear are at different heights. 
     In a further aspect, the driven shaft is a propeller shaft having a propeller mounted thereon. 
     In a further aspect, the first and second driving gears are first and second pinion gears, and the at least one driven gear is at least one bull gear. 
     In a further aspect, the at least one height adjustment member is a shim placed on only one of the first driveshaft and the second driveshaft. 
     In a further aspect, the at least one height adjustment member is at least one threaded height adjustment member disposed below at least one of the first and second helical gears. 
     In a further aspect, the at least one driven gear is a single driven gear. The driven gear engages the first and second driving gears. 
     In a further aspect, the at least one driven gear comprises first and second driven gears. The first driven gear engages the first driving gear. The second driven gear engages the second driving gear. 
     In an additional aspect, the invention provides a method of assembling a marine outboard engine having an engine casing. A first driveshaft has a first end and a second end. The first end has a first helical gear disposed thereon. The second end has a first driving gear disposed thereon. A second driveshaft has a first end and a second end. The first end has a second helical gear disposed thereon. The second end has a second driving gear disposed thereon. At least one height adjustment member is associated with at least one of the first and second helical gears. The at least one height adjustment member is movable between a first position and a second position vertically higher than the first position. A driven shaft has at least one driven gear disposed thereon. The method comprises: placing the first driveshaft in the engine casing such that the first helical gear is free to move in an axial direction relative to the engine casing; placing the driven shaft in the engine casing such that one of the at least one driven gear meshes with the first driving gear; placing the second driveshaft in the engine casing such that: the second driving gear meshes with one of the at least one driven gear, the first helical gear meshes with the second helical gear, and the second helical gear is free to move in an axial direction relative to the engine casing; rotating the driven shaft to cause an axial displacement of one of the first and second helical gears with respect to the engine casing as a result of the rotation of the driven shaft; and moving the at least one height adjustment member from the first position to the second position, the height of the second position being determined based at least in part on the magnitude of the relative axial displacement. 
     In a further aspect, the method further comprises fixing the first and second helical gears in position after moving the at least one height adjustment member, such that axial movement of the first and second helical gears in an axial direction is substantially prevented. 
     In a further aspect, the at least one height adjustment member is at least one threaded height adjustment member. Moving the at least one height adjustment member comprises rotating the at least one height adjustment member. 
     In a further aspect, the at least one driven gear is a single driven gear. Placing the driven shaft in the engine casing such that one of the at least one driven gear meshes with the first driving gear comprises placing the driven shaft in the engine casing such that the driven gear meshes with the first driving gear. Placing the second driveshaft in the engine casing such that the second driving gear meshes with one of the at least one driven gear comprises placing the second driveshaft in the engine casing such that the second driving gear meshes with the driven gear. 
     In a further aspect, the at least one driven gear comprises first and second driven gears. Placing the driven shaft in the engine casing such that one of the at least one driven gear meshes with the first driving gear comprises placing the driven shaft in the engine casing such that the first driven gear meshes with the first driving gear. Placing the second driveshaft in the engine casing such that the second driving gear meshes with one of the at least one driven gear comprises placing the second driveshaft in the engine casing such that the second driving gear meshes with the second driven gear. 
     In the present application, terms related to spatial orientation such as forwardly, rearwardly, left, and right, should be interpreted are as they would normally be understood by a driver of a watercraft sitting thereon in a normal driving position, when the engine is mounted on the watercraft. In addition, the term “axial direction”, when used in reference to a particular shaft, refers to a direction along the longitudinal axis of that shaft. 
     Embodiments of the present invention each have at least one of the above-mentioned objects and/or aspects, but do not necessarily have all of them. It should be understood that some aspects of the present invention that have resulted from attempting to attain the above-mentioned objects may not satisfy these objects and/or may satisfy other objects not specifically recited herein. 
     Additional and/or alternative features, aspects, and advantages of embodiments of the present invention will become apparent from the following description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where: 
         FIG. 1  is a side elevation view of a marine outboard engine to which the present invention can be applied; 
         FIG. 2  is a partial cross-sectional view of an outboard engine to which the present invention can be applied; 
         FIG. 3  is a logic diagram of a method of assembling an outboard engine according to the present invention; 
         FIG. 4  is a partial cross-sectional view of an outboard engine assembled using the method of  FIG. 3 ; 
         FIG. 5  is a partial cross-sectional view of an outboard engine according to a second embodiment; 
         FIG. 6A  is a partial cross-sectional view of an outboard engine according to a third embodiment; and 
         FIG. 6B  is a partial cross-sectional view of an outboard engine according to a fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a marine outboard engine  40  will be described according to a first embodiment. It should be understood that the present invention is applicable to other marine applications involving propellers, such as inboard engines and stern drives. 
       FIG. 1  is a side view of a marine outboard engine  40  having a cowling  42 . The cowling  42  surrounds and protects an engine  44 , shown schematically. The engine  44  may be any suitable engine known in the art, such as an internal combustion engine. An exhaust system  46 , shown schematically, is connected to the engine  44  and is also surrounded by the cowling  42 . 
     The engine  44  is coupled to two vertically oriented driveshafts  48  and  49 . The driveshafts  48 ,  49  are coupled to a drive mechanism  50 , which includes a transmission  52  and a bladed rotor, such as a propeller  54  mounted on a propeller shaft  56 . The driveshafts  48 ,  49  and the transmission  52  will be described below in greater detail. The propeller shaft  56  is generally perpendicular to the driveshafts  48 ,  49 . The drive mechanism  50  could also include a jet propulsion device, turbine or other known propelling device. Other known components of an engine assembly are included within the cowling  42 , such as a starter motor and an alternator. As it is believed that these components would be readily recognized by one of ordinary skill in the art, further explanation and description of these components will not be provided herein. 
     A stern bracket  58  is connected to the cowling  42  via the swivel bracket  59  for mounting the outboard engine  40  to a watercraft. The stern bracket  58  can take various forms, the details of which are conventionally known. 
     A linkage  60  is operatively connected to the cowling  42 , to allow steering of the outboard engine  40  when coupled to a steering mechanism of a watercraft, such as a steering wheel. 
     The cowling  42  includes several primary components, including an upper motor cover  62  with a top cap  64 , and a lower motor cover  66 . A lowermost portion, commonly called the gear case  68 , is attached to the exhaust system  46 . The upper motor cover  62  preferably encloses the top portion of the engine  44 . The lower motor cover  66  surrounds the remainder of the engine  44  and the exhaust system  46 . The gear case  68  encloses the transmission  52  and supports the drive mechanism  50 , in a known manner. The propeller shaft  56  extends from the gear case  68  and supports the propeller  54 . 
     The upper motor cover  62  and the lower motor cover  66  are made of sheet material, preferably plastic, but could also be metal, composite or the like. The lower motor cover  66  and/or other components of the cowling  42  can be formed as a single piece or as several pieces. For example, the lower motor cover  66  can be formed as two lateral pieces that mate along a vertical joint. The lower motor cover  66 , which is also made of sheet material, is preferably made of composite, but could also be plastic or metal. One suitable composite is fiberglass. 
     A lower edge  70  of the upper motor cover  62  mates in a sealing relationship with an upper edge  72  of the lower motor cover  66 . A seal  74  is disposed between the lower edge  70  of the upper motor cover  62  and the upper edge  72  of the lower motor cover  66  to form a watertight connection. 
     A locking mechanism  76  is provided on at least one of the sides of the cowling  42 . Preferably, locking mechanisms  76  are provided on each side of the cowling  42 . 
     The upper motor cover  62  is formed with two parts, but could also be a single cover. As seen in  FIG. 1 , the upper motor cover  62  includes an air intake portion  78  formed as a recessed portion on the rear of the cowling  42 . The air intake portion  78  is configured to prevent water from entering the interior of the cowling  42  and reaching the engine  44 . Such a configuration can include a tortuous path. The top cap  64  fits over the upper motor cover  62  in a sealing relationship and preferably defines a portion of the air intake portion  78 . Alternatively, the air intake portion  78  can be wholly formed in the upper motor cover  62  or even the lower motor cover  66 . 
     Referring to  FIG. 2 , the mechanism by which the engine  44  drives the propeller  54  will now be described in more detail. 
     The output shaft  51  of the engine  44  is coupled to the driveshaft  48 . It is contemplated that the output shaft  51  of the engine  44  may be coupled to the driveshaft  48  via a gear arrangement or any other suitable connection. It is further contemplated that the output shaft  51  may instead be coupled to the driveshaft  49 . A helical gear  80  is mounted on the driveshaft  48  via a spline connection or any other suitable connection. The gear  80  meshes with a second helical gear  82  that is splined or otherwise suitably mounted on the driveshaft  49 , such that the engine  44  drives both driveshafts  48 ,  49  simultaneously to rotate in opposite directions at the same rotational speed. The helical gears  80 ,  82  arc preferably slidably mounted to the respective driveshafts  48 ,  49  via the spline connections and free to move with respect thereto along an axial direction of the driveshafts  48 ,  49 . 
     A first pinion gear  84  is mounted to the bottom of the driveshaft  48 , and a second pinion gear  86  is mounted to the bottom of the driveshaft  49 . The propeller shaft  56  is supported below the driveshafts  48 ,  49  by bearings  92  that are preferably tapered roller bearings capable of partially absorbing the forces exerted on the propeller shaft  56  by the propeller  54  while the engine  40  is in use. The tapered roller bearings  92  are preferably pre-loaded to better absorb the forces on the propeller shaft  56 . A bull gear  88  is splined on the propeller shaft  56  such that the bull gear  88  is free to move axially along the propeller shaft  56  in response to loads exerted thereon. The bull gear  88  is disposed between the two pinion gears  84 ,  86 , and is suitably shaped so that each of the pinion gears  84 ,  86  meshes with the teeth on one side of the bull gear  88 . The pinion gears  84 ,  86  rotate in opposite directions, and as a result the portions of the pinion gears  84 ,  86  that are in contact with the bull gear  88  drive the bull gear  88  in the same direction, thereby rotating the propeller shaft  56  to drive the propeller  54 . 
     Referring to  FIG. 3 , a method of assembling the outboard engine  40  will now be described according to an embodiment of the invention, starting at step  100 . 
     At step  110 , the driveshaft  49  is installed in the outboard engine  40  such that the gear  86  is disposed within the gear case  68 . A shoulder  91  (shown in  FIG. 2 ) extends radially outward from the helical gear  82  and is supported on a part of the engine  40  such that the helical gear  82  is free to move upward in an axial direction. 
     At step  120 , the propeller shaft  56  and bull gear  88  are installed in the gear case  68 , such that the bull gear  88  meshes with the gear  86 . 
     At step  130 , the driveshaft  48  is installed in the outboard engine  40  parallel to the driveshaft  49 , such that the gear  84  is disposed within the gear case  68  and meshes with the bull gear  88 . A shoulder  90  (shown in  FIG. 2 ) extends radially outward from the helical gear  80  and is supported on a part of the engine  40  such that the helical gear  80  is free to move upward in an axial direction. 
     At step  140 , the helical gears  80  and  82  are disposed on the driveshafts  48  and  49 , respectively, such that the gears  80  and  82  mesh with each other. 
     At step  150 , two position indicators (not shown) are placed on the top of the respective gears  80 ,  82  so that their vertical position can be measured relative to a reference position. It is contemplated that the position indicators may be any suitable indicators known in the art that allow a determination of how far either of the helical gears  80 ,  82  has moved relative to the reference position. The reference position may be the initial position of either helical gear  80 ,  82  or the position of any reference object such as a part of the outboard engine  40  with respect to which either helical gear  80 ,  82  may move. It is contemplated that only a single position indicator may be used, by placing the position indicator on one or the other of the respective gears  80 ,  82 . If only a single position indicator is used, and the gear  80 ,  82  that moves vertically is not the one on which the position indicator was placed, it may be necessary to repeat steps  150 - 190  with the position indicator placed on the other one of the gears  80 ,  82 . 
     At step  160 , the propeller shaft  56  is driven in either the clockwise or the counter-clockwise direction by an external force. The direction in which the propeller shaft  56  is driven is the direction opposite the normal forward direction of rotation of the propeller shaft  56  when the outboard engine  40  is in operation. The external force may be applied by a machine that exerts a torque on the propeller shaft  56 , or by a person manually turning the propeller shaft  56 . The rotation of the propeller shaft  56  drives the bull gear  88 , which in turn drives the gears  84  and  86 . 
     At step  170 , the load exerted by the bull gear  88  is either balanced between the gears  84  and  86 , or unbalanced such that a higher load is exerted on one or the other of the gears  84  and  86 . 
     At step  180 , if the load from the bull gear  88  is evenly balanced between the gears  84  and  86 , the helical gears  80 ,  82  will remain in position. The process continues at step  220 . 
     At step  190 , if the load from the bull gear  88  is unbalanced between the gears  84  and  86 , one of the driveshafts  48 ,  49  will be driven with a higher load than the other of the driveshafts  48 ,  49 . As a result, the driveshaft  48 ,  49  with the higher load will attempt to rotate at a faster rate than the driveshaft  48 , as long as the loads remain unbalanced. The faster rate of rotation of one of the driveshafts  48 ,  49 , in combination with the angled threads of the helical gears  80 ,  82 , causes one of the helical gears  80 ,  82  to move upwardly relative to the other helical gear  80 ,  82 . Whether it is the helical gear  80  or the helical gear  82  that moves upwardly will depend on a combination of the direction of rotation of the driveshafts  48 ,  49 , the handedness of the helical gears  80 ,  82  and which of the driveshafts  48 ,  49  experiences the higher load.  FIG. 4  schematically illustrates the case in which the propeller shaft  56  is rotated counter-clockwise as seen from the rear of the outboard engine  40  (indicated by the arrow), the helical gear  80  is right-handed, the helical gear  82  is left-handed, and the driveshaft  49  is driven with a higher load than the driveshaft  48 . In this case, the helical gear  82  will move upwardly as shown. The effects of other combinations of these parameters should be readily understood by persons skilled in the art, and will not be discussed herein in detail. Once the helical gears  80 ,  82  have reached a stable configuration in which the load from the bull gear  88  is evenly balanced between the gears  84  and  86 , the helical gears  80 ,  82  no longer move vertically relative to each other. The helical gear  82  is raised with respect to the helical gear  80  by a distance L (shown in  FIG. 4 ). The distance L is measured using the position indicator. 
     At step  200 , a shim  94  (shown in  FIG. 4 ) is selected having a thickness L. 
     At step  210 , the shim  94  is inserted below the shoulder  91  of the raised helical gear  82  to maintain it in the raised position corresponding to a balanced load between the helical gears  80 ,  82 . For example, if the distance L was measured to be 0.5 mm at step  190 , a shim  94  having a thickness of 0.5 mm will be selected and inserted, as seen in  FIG. 4 . 
     At step  220 , the installation of the helical gears  80 ,  82  in the outboard engine  40  is completed, such that the helical gears  80 ,  82  are fixed in position and are no longer free to move relative to each other in an axial direction. The helical gears  80 ,  82  may be fixed in position in any suitable way, such as by applying a threaded lock nut (not shown) to a threaded portion (not shown) on one end of each driveshaft  48 ,  49 . 
     At step  230 , the remaining components of the outboard engine  40  are attached. 
     The process ends at step  240 . 
     It is contemplated that some of the above steps may be performed in a different order. For example, the helical gears  80 ,  82  may be placed on the respective driveshafts  48 ,  49  before the driveshafts  48 ,  49  are installed in the outboard engine  20 . In addition, the driveshafts  48 ,  49  and the propeller shaft  56  may be installed in any convenient order. 
     Referring to  FIG. 5 , a portion of a marine outboard engine (not shown) will be described according to an alternative embodiment. 
     The helical gears  180 ,  182  are respectively mounted on the driveshafts  48 ,  49  in the same manner as the helical gears  80 ,  82  of  FIGS. 2 and 4 . The helical gears  180 ,  182  are supported respectively by shoulders  190  and  191  that form part of height adjusting members  192 ,  193  respectively. Each height adjustment member  192 ,  193  has a threaded exterior surface that engages a corresponding threaded opening  194 ,  195 . Threaded lock nuts  196 ,  197  engage the threaded surfaces of the corresponding height adjustment members  192 ,  193  and can be adjusted to lock the height adjustment members  192 ,  193  and prevent them from moving in an axial direction of the shafts  148 ,  149 . The remaining parts of the outboard engine of the present embodiment are similar in structure and function to the parts of the outboard engine  40 , and will not be described in detail. 
     When the method of  FIG. 3  is performed on the engine of  FIG. 5 , the measurement of the distance L in step  190 , as well as steps  200  and  210 , are replaced by a step in which the height of the height adjustment member  193  corresponding to the raised gear  182  is raised by the distance L, preferably by using a wrench or other suitable tool to grip a suitably-shaped extension  199  on the height adjustment member  193  and rotating the height adjustment member  193  until the desired height is reached. A similarly-shaped extension  198  is provided on the height adjustment member  192 . 
     At step  220 , the helical gears  180  and  182  are fixed in position by adjusting the lock nuts  196 ,  197 . 
     The remaining steps are carried out as in the embodiment of  FIG. 3 , and will not be described again in detail. 
     Referring to  FIG. 6A , a driven gear arrangement will be described according to an alternative embodiment. Two bull gears  288 ,  289  are mounted on the driveshaft  56  between the pinion gears  84 ,  86 , in a similar manner to the bull gear  88  of  FIGS. 2 and 4 . The bull gear  288  meshes with the pinion gear  84 , and the bull gear  289  meshes with the pinion gear  86 . When the outboard engine  40  is in use, the pinion gears  84 ,  86  drive the bull gears  288 ,  289  respectively, to drive the propeller  54 . The remaining components of the outboard engine are similar to those of the embodiment shown in  FIGS. 2 and 4 , and will not be described again in detail. 
     Referring to  FIG. 6B , a driven gear arrangement will be described according to an alternative embodiment. Two bull gears  388 ,  389  are mounted on the driveshaft  56 , in a similar manner to the bull gear  88  of  FIGS. 2 and 4 . The bull gear  388  is mounted between the pinion gear  84  and the bearing  392 . The bull gear  388  meshes with the pinion gear  84 . The bull gear  389  is mounted between the pinion gear  86  and the bearing  393 . The bull gear  389  meshes with the pinion gear  86 . When the outboard engine  40  is in use, the pinion gears  84 ,  86  drive the bull gears  388 ,  389  respectively, to drive the propeller  54 . The remaining components of the outboard engine are similar to those of the embodiment shown in  FIGS. 2 and 4 , and will not be described again in detail. 
     Modifications and improvements to the above-described embodiments of the present invention may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the present invention is therefore intended to be limited solely by the scope of the appended claims.