Abstract:
A motorcycle has a cylinder bore that is vertically offset from a crankshaft. A camshaft also is vertically offset from the cylinder bore. The offsets decrease the vertical dimension of the engine. An air induction system approaches a cylinder head from the rear to limit the degree to which the induction system extends forward of the engine. By decreasing the envelope of the engine, more space is provided on the scooter-type motorcycle for a foot rest forward of the engine and a storage compartment above the engine.

Description:
PRIORITY INFORMATION 
   This application is based on and claims priority to Japanese Patent Application No. 2003-355295, filed Oct. 15, 2003, the entire contents of which is hereby expressly incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a motorcycle and an engine thereof. More particularly, the present invention relates to an engine configuration that reduces the overall size of the engine such that a footrest and/or storage compartment size can be increased. 
   2. Description of the Related Art 
   Motor scooters and other forms of motorcycles generally comprise an engine that is positioned vertically below a seat. Moreover, the engine generally is positioned rearward of a footrest. For example, as shown in Japanese Patent Publication No. 2003-222054, published on Aug. 8, 2003 and filed as Japanese Patent Application No. 2002-19643 on Jan. 29, 2002, the engine is positioned rearward of the footrest and below the seat. Due to this placement, the engine features a cylinder axis that is offset relative to an axis of a corresponding crankshaft. The offset orientation allows the cylinder body to be positioned lower than would otherwise be possible if the cylinder axis extended through the crankshaft axis. Thus, the vertical height of the engine can be somewhat reduced. 
   SUMMARY OF THE INVENTION 
   Nevertheless, it has been found that the engine of the above-identified publication remains too large in a vertical direction and/or a direction defined by the forward and rearward direction of the motorcycle. In particular, the air induction system extends upward and forward from the engine to accommodate a helmet storage compartment. The placement of the induction system, however, increases the length of the engine and decreases the available room for a foot rest. Moreover, due to the vertical size of the engine in the above-identified publication, the induction system cannot easily be routed in another direction. 
   Thus, one aspect of the present invention involves recognition of a need for reducing the size of the engine in the fore-and-aft direction and/or in the vertical direction. Thus, a motorcycle can be provided with an engine that is reduced in size in one or both of these directions such that space for arranging a foot rest can be increased and/or space for a storage box with an increased volume can be provided. 
   Another aspect of the present invention involves a motorcycle comprising a footrest and an engine. The footrest is positioned forward of the engine. The engine comprises a cylinder body, a cylinder head and a crankcase. The cylinder body is positioned between the cylinder head and the crankcase. The cylinder head is closer to the footrest than the crankcase. An induction system communicates with the cylinder head on an upper surface of the cylinder head. The induction system comprises an intake passage with an upstream direction that extends rearward from the cylinder head. The cylinder body comprises a central axis. A crankshaft is positioned within the crankcase. The crankshaft extends generally transversely and comprises a rotational axis. A rearwardly extending imaginary extension along the central axis of the cylinder body extends below the rotational axis of the crankshaft such that the cylinder body is offset relative to the crankshaft. 
   An additional aspect of the present invention involves a motorcycle comprising an engine. The engine comprises a cylinder body and a cylinder head. The cylinder body comprises a cylinder bore. The cylinder bore comprises a central axis. A crankcase is connected to the cylinder body. The crankcase contains a crankshaft. The crankshaft comprises a rotational axis. The cylinder body is connected to the cylinder head. The cylinder body is positioned between the cylinder head and the cylinder body. The cylinder head is positioned generally forward of the cylinder body. The cylinder body is positioned generally forward of the crankcase. The engine also comprises a valve train. The valve train comprises a single camshaft. The camshaft comprises a transverse rotational axis. The camshaft is operably connected to an intake valve and an exhaust valve such that rotation of the camshaft about the transverse rotational axis results in opening and closing of the intake valve and the exhaust valve. The cylinder body is offset relative to the crankshaft such that the rotational axis of the crankshaft and the central axis of the cylinder bore do not intersect and the cylinder body is offset relative to the camshaft such that the transverse rotational axis of the camshaft and the central axis of the cylinder bore do not intersect. 
   A further aspect of the present invention involves a motorcycle comprising an engine. The engine comprises a cylinder body and a cylinder head. The cylinder head defines a cam chamber. A cam shaft is positioned within the cam chamber. The camshaft comprises a cam axis. A drive member is secured to the cam shaft. The cylinder body is connected to the cylinder head with the cylinder head being positioned generally forward of the cylinder body. A crankcase is connected to the cylinder body. The cylinder body is positioned generally forward of the crankcase. The crankcase contains a crankshaft. The crankshaft is adapted to rotated about a rotational axis. The cylinder body defines a cylinder bore. The cylinder bore comprises a central axis. An exhaust pipe is connected to a generally downwardly facing surface of the cylinder head. The cylinder body is offset relative to the crankshaft such that a rearwardly extending imaginary extension of the central axis extends below the rotational axis of the crankshaft. An interface between the cylinder head and the exhaust pipe is generally vertically aligned with a lower wall of the cylinder head proximate the drive member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects and advantages of the present invention will now be described with reference to the drawings of a more than one preferred embodiment, which embodiments are intended to illustrate and not to limit the invention. The drawings comprise eight figures. 
       FIG. 1  is a left side view of a motorcycle that is arranged and configured in accordance with certain features, aspects and advantages of the present invention. 
       FIG. 2  is a plan view of a rear portion of the motorcycle of  FIG. 1 . 
       FIG. 3  is a sectioned plan view taken through an engine unit of the motorcycle of  FIG. 1 . 
       FIG. 4  is a sectioned left side view of a portion of an engine of the engine unit shown in  FIG. 3 . This view shows a cam shaft, a pair of valves, a combustion chamber, a piston and the connecting rod. 
       FIG. 5  is sectioned left side view of another portion of the engine of the engine unit shown in  FIG. 3 . This view shows a cam shaft drive system. 
       FIG. 6  is a right side view of the engine of the engine unit shown in  FIG. 3 . 
       FIG. 7  is a sectioned plan view of a portion of a cylinder body, piston and connecting rod of an engine that is arranged and configured in accordance with certain features, aspects and advantages of the present invention. 
       FIG. 8  is a sectioned left side view of the cylinder body, piston and connecting rod shown in  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference to  FIGS. 1 to 6 , a motorcycle  1  and engine unit  5  are illustrated that have been arranged and configured in accordance with certain features, aspects and advantages of the present invention.  FIG. 1  and  FIG. 2  are a left side view and a plan view of a scooter type motorcycle.  FIG. 3  is a sectional plan exploded view of an engine unit.  FIG. 4  is a sectional left side view of a main portion of an engine of the engine unit.  FIG. 5  is a sectional left side view of the engine unit.  FIG. 6  is a right side view of a main portion of the engine. As used in the description, “front”, “rear”, “left”, and “right” mean “front”, “rear”, “left”, and “right” as viewed by a person sitting on a seat of the scooter type motorcycle in an operating position. 
   In the drawings, a reference numeral  1  denotes a scooter type motorcycle. The illustrated motorcycle  1  comprises a front wheel  4  that is rotatably supported by a front fork  3 . The front fork is supported in such a manner as to be steered to the left and right by a head pipe  2   a  provided on the front end of a vehicle frame  2 . A swing type engine unit  5  is arranged under a rear frame  2   b . The engine unit  5  is supported for movement in an up and down direction relative to the rear frame  2   b . A rear wheel  6  is rotatably supported by the rear end portion of the engine unit  5  and a storage box  7  is arranged above the engine unit  5 . An opening at the top end of the storage box  7  is opened or closed by a seat (not shown). Preferably, the frame  2  and the storage box  7  are surrounded by a covering member. 
   In one arrangement, the engine unit  5  comprises a water-cooled 4-cycle single cylinder type engine body  8 . Other types of engines also can be used. The engine body comprises a crankcase  9  that is divided into a right case  9   a  and a left case  9   b . The engine unit  5  also comprises a transmission case  10  that extends rearward from the engine body  8 . Preferably, the engine body  8  and the transmission case  10  are secured together to form the integrated engine unit  5 . 
   The transmission case  10  comprises a case body  10   a  that extends rearward from the left case  9   a  of the crankcase. The case body  10   a  can be integrally formed with a portion of the crankcase. A case cover  10   b  can be removably mounted on the outside of the case body  10   a.    
   A belt type continuously variable transmission (CVT)  11  is arranged in this transmission case  10 . The CVT  11  generally comprises a driving pulley  11   a  that is mounted to the crankshaft  12 . In the illustrated arrangement, the CVT  11  is mounted to the left end of the crankshaft. The CVT  11  also comprises a driven pulley  11   b  that is mounted to an intermediate shaft  13 . In the illustrated arrangement, the driven pulley  11   b  is closer to the rear wheel than the drive pulley  11   a . A V belt  11   c  or any other suitable flexible endless transmitter can be looped over the driving pulley  11   a  and the driven pulley  11   b . As illustrated, the intermediate shaft  13  preferably is coupled via a gear mechanism to a rear wheel shaft  13   a  and the rear wheel  6  is fixed to the rear wheel shaft  13   a.    
   The engine body  8  generally comprises a cylinder body  14 , a cylinder head  15  and a head cover  16 . The cylinder head  15  preferably is interposed between the cylinder body  14  and the head cover  16 . Moreover, in the illustrated arrangement, the head cover  16  is positioned forward of the cylinder head  15  and the cylinder head  15  is positioned forward of the cylinder body  14 . The cylinder body  14  preferably is connected to the front wall  9   c  of the crankcase  9 . A piston  17  can be inserted into a cylinder bore  14   a  defined within the cylinder body  14  and the piston  17  can be coupled to the crankshaft  12  by a connecting rod  18 . 
   With reference to  FIG. 4 , the engine body  8  preferably comprises at least one, and more preferably two, intake valve openings  15   b . The engine body  8  also preferably comprises at least one exhaust valve opening  15   c . The intake valve openings  15   b  and the exhaust valve opening  15   c  preferably are formed in a depression  15   a  that is formed at the cylinder body  14  side mating face of the cylinder head  15 . The depression  15   a  at least partially defines a combustion chamber. 
   The illustrated intake valve openings  15   b  communicate with the upper wall  15   e  of the cylinder head  15  through an intake port  15   d . The intake port  15   d  defines at least a portion of an intake passage. An outside mounting face  15   h  of the intake port  15   d  preferably is generally perpendicular or normal to a face of the cylinder head that abuts the cylinder body  14 . In one arrangement, the outside mounting face  15   h  is substantially flush with the upper wall  15   e  of the cylinder head. Furthermore, the upper wall  15   e  of the cylinder head preferably is slightly higher in the region above a chain chamber portion  15   e ′ of the wall  15   e  corresponding to a chain chamber  15   j  through which a cam chain, cam belt or the like  25  extends than the portion of the wall that is closer to the cylinder body  14 . Preferably, a drive member, such as a sprocket, gear, pulley or the like is used on both the camshaft and the crankshaft to connect the camshaft and crankshaft with the cam timing chain or belt, for instance. The illustrated chain chamber and cam chamber forms a generally compact engine structure while providing ample volume within the cylinder head  15  to accommodate the cam chain  25  and other related components. 
   With continued reference to  FIG. 4 , the exhaust valve opening  15   c  communicates with a lower wall  15   g  through an exhaust port  15   f  that defines at least a portion of an exhaust passage. The outside mounting face  15   i  of the exhaust port  15   f  preferably is recessed into the lower wall  15   g . Notwithstanding the preferred recessed arrangement of the outside mounting face  15   i , the outside mounting face  15   i  preferably extends downward nearly to the same degree as the portion  15   g ′ of the lower wall  15   g  that corresponds to the chain chamber  15   j.    
   The intake valve  19   a  and the exhaust valve  19   b  are arranged at the intake valve opening  15   b  and the exhaust valve opening  15   c , respectively, and the intake valve  19   a  and the exhaust valve  19   b  are opened or closed via intake and exhaust rocker arms  21   a  and  21   b  by one camshaft  20 . 
   With reference still to  FIG. 4 , when viewed from the side of the vehicle, the cylinder body  14 , the cylinder head  15  and the head cover  16  are arranged such that they are leaning toward the front of the motorcycle  1  with an axis B of the cylinder bore  14   a  being slightly higher at the front side with respect to a horizontal line. More preferably, these components are arranged at an offset position in such a way that the axis B of the cylinder bore  14   a  is positioned below the axis  12   a  of the crankshaft  12  by a distance of “a”. Even more preferably, the camshaft  20  can be offset in such a way that its axis  20   a  is positioned below the axis B of the cylinder bore  14   a  by a distance of “b” (see  FIG. 4  and  FIG. 5 ). The offset positions of the components advantageously lower the respective components and create more open space above the engine. 
   With reference to  FIG. 3 , when the engine unit  5  is viewed in plan view, the engine body  8  preferably is positioned relative to a longitudinal center plane L of the vehicle such that the axis b of the cylinder bore is offset to the left with respect to the center plane L by a distance of c. As illustrated, the pump shaft  28   a  of a coolant pump  28  preferably is coupled to the camshaft  20 . In one arrangement, the pump shaft  28   a  is coupled to the left end of the camshaft  20 . In another arrangement, the pump shaft  28   a  is integrally formed with the camshaft  20 . As illustrated in  FIG. 1 , coolant discharged from the coolant pump  28  can be routed through a return hose  29   a  arranged so as to pass below the cylinder head  15  to a radiator  30  (see  FIG. 6 ) arranged on the right side of the vehicle. A supply house  29   b  routes the coolant from the radiator  30  to a cooling jacket that is used to cool the engine body  8 . 
   With reference to  FIG. 3 , the radiator  30  advantageously is positioned within, or adjacent to, a wind introducing cover  31   b . The cover  31   b  in the illustrated arrangement is positioned on the right side of the crankcase  9 . Preferably, the cover  31   b  is removably mounted on a fan casing  31   a . More preferably, the cover  31   b  is positioned in such a way as to cover the right end portion of the right case  9   b  of the crankcase  9 . A fan  32  can be mounted on the crankshaft  12  or any suitable shaft. Advantageously, the fan  32  is positioned within the casing  31   a.    
   With continued reference to  FIG. 3 , an ignition coil  33  preferably is arranged along a front wall  16   a  of the head cover  16 . More preferably, the ignition coil  33  is positioned outside of the head cover  16  but adjacent thereto. The ignition coil  33  can be retained by a support boss portion  16   b  formed in the head cover  16 . 
   In the illustrated arrangement, the ignition coil  33  is arranged with its axis pointed in a transverse direction of the vehicle such that a primary coil  33   a  faces to the right side of the vehicle and a secondary coil  33   b  faces to the left side. The primary coil  33   a  merges with a main harness arranged in such a way as to extend along the right side of the vehicle and the secondary coil  33   b  extends from the left side of the ignition coil  33  to the right side of the vehicle. The secondary coil  33   b  is connected to a plug cap  33   c . The plug cap  33   c  is mounted on the ignition plug  34 . In the illustrated arrangement, the ignition plug is arranged on the right side of the cylinder head  15 . Other positions also are possible. 
   Because the ignition coil  33  is fixed to the head cover  16 , a distance between the ignition plug  34  and the secondary coil  33   b  is minimized. In addition, the secondary coil  33   b  is constructed to extend from the left side of the ignition coil  33  to the right side so that the secondary coil  33   b  can be shortened while facilitating easy mounting and removal of the plug cap with the ignition plug  34 . In other words, by routing the secondary coil  33   b  in the manner described, sufficient length is provided to allow the cap to be easily placed on and removed from the ignition plug  34 . 
   The exhaust pipe  22   a  of an exhaust device  22  is connected to the outside mounting opening  15   i  of the exhaust port  15   f . The outside mounting opening  15   i  is recessed from the lower wall  15   g  of the cylinder head  15  as described above, so that while the camshaft  20  can be arranged at a lower offset position, sufficient road clearance is provided to the exhaust pipe  22   a  while the exhaust pipe  22   a  can be maintained at a sufficiently large diameter. 
   An intake manifold  23  defines a portion of an intake passage. The manifold  23  is connected to the outside mounting face  15   h  of the intake port  15   d , which defines a portion of the intake passage. The intake manifold  23  and the intake port  15   d  advantageously are formed in a smoothly continuous arc. In the illustrated arrangement, the intake manifold  23  and the intake port  15   d  generally define a semicircle and a carburetor body (i.e., a member for varying a passage area)  24  is connected to the upstream end of the intake manifold  23 . The carburetor body  24  preferably comprises a throttle valve  24   a  that is provided on the downstream side of a venturi portion of the intake passage. The carburetor body  24  also preferably comprises a diaphragm chamber  24   b  and a float chamber  24   c , which can be provided on the upper side and on the lower side of the venturi portion, respectively. In some arrangements, a recess  7   a  can be formed in a lower portion of the storage box  7  to reduce the likelihood of contact between the carburetor body  24  and the storage box  7 . If the engine comprises a fuel injection valve, a throttle body comprising a throttle valve can be provided as the member for varying a passage area. 
   The carburetor body  24  inclines to the right side of the illustrated vehicle when viewed in plan view and an intake duct  26  preferably is connected to the intake port  24   d  of the carburetor body  24 . In the illustrated arrangement, the intake duct  26  bends to the left side of the vehicle and its upstream end portion is connected to an air cleaner  27 . The air cleaner can be positioned in any suitable position and, in one arrangement, can be arranged on top of the transmission case  10 . 
   The engine can be mounted in any suitable manner. In the illustrated arrangement, an engine suspension boss portion (engine suspension portion)  9   d  can be integrally formed with the upper wall  9   e  of the crankcase  9  on the rear side of the carburetor body  24 . The suspension boss portion  9   d  can be supported to pivot up and down direction about a support shaft  9   f  (see  FIG. 1 ). In the illustrated arrangement, a support bracket  2   c  is fixed to the rear frame  2   b  and the support bracket  2   c  journals the shaft  9   f . Other arrangements also can be used to secure the engine unit to the rear frame  2   b.    
   With reference to  FIG. 4 , the upper wall  15   e  of the cylinder head  15  and the upper wall  9   e of the crankcase  9  extend further upward than the upper wall of the cylinder body  14  such that a depression is defined between the crankcase  9  and the cylinder head  15 . As illustrated, the carburetor body  24  is positioned forward of the suspension boss portion  9   d  and the lower portion of the float chamber  24   c  is disposed lower than a line “e” that connects the upper walls  15   e  and  9   e . Thus, at least a portion of the carburetor body  24  is positioned within a recess defined between the cylinder head  15  and the crankcase  9 . In this manner, the carburetor body  24  is arranged in such a way as to be positioned generally adjacent to the cylinder body  14 . While the radius of curvature of the intake passage, which is at least partially defined by the intake port  15   d  and intake manifold  23 , can be set at a size capable of reducing flow resistance, the carburetor body  24  can be positioned close to the cylinder body  14 , whereby the engine can be reduced in height in the generally vertical direction. As a result, the volume of the storage box can be increased into the region that would otherwise be occupied by one or more of these components. Moreover, because the intake manifold  23  extends generally rearward, the intake manifold, the carburetor body and other intake components advantageously are positioned in regions other than the region of the foot rest F (schematically shown) such that an increased foot rest size can be provided. 
   With reference still to  FIG. 4 , an oil pan  9   h  advantageously is formed in the bottom wall of the crankcase  9 . The front end portion of the oil pan  9   h  preferably is located forward of the midpoint in the axial direction of the cylinder body  14 . In one presently preferred arrangement, the forward end of the oil pan  9   h  is positioned near the rear end of a skirt portion  17   a  of the piston  17  when the piston is located in top dead center. 
   As illustrated, the cylinder body  14  desirably is offset such that its cylinder axis B extends below the axis  12   a  of the crankshaft  12 . In addition, at least the intake manifold  23  extends generally rearward from the upper wall  15   e  of the cylinder head  15 . Moreover, the carburetor body  24  is connected to the intake manifold  23 . Hence, the arrangement of the cylinder body  14  at the lower offset position can further reduce the total height of the engine and can accordingly increase the volume of the storage box  7 . 
   With reference still to  FIG. 4 , a valve train is provided that drives the intake and exhaust valves. The valve train advantageously has a structure in which one camshaft  20  can be generally centrally arranged within the cylinder head  15  in the vertical direction. By using a single camshaft  20  to operate the intake valves and the exhaust valves, unlike the case where two camshafts are used, the upper wall portion of the cylinder head does not need to be expanded upward to provide adequate operating room for the camshaft and any related valve train components. Thus, the single cam shaft construction further reduces the overall height of the engine. 
   With reference to  FIG. 5 , the camshaft  20  preferably is offset lower than the cylinder axis B. By offsetting the camshaft  20 , the intake valve  19   a  located on the upper wall  15   e  side of the cylinder head  15  can extend more along the direction of the cylinder axis B. In other words, the intake valve  19   a  can extend at a smaller angle relative to the exhaust valve. The reorientation of the intake valve  19   a  also acts to reduce the height of the upper wall  15   e  of the cylinder head  15  and, hence, helps to reduce the overall height of the engine. 
   Still further, the cylinder head side connection face  15   h  of the intake manifold (intake passage)  23  is perpendicular to the cylinder body side mating face of the cylinder head  15  and is located at a position higher than a portion  15   e ′ corresponding to the cam chain arrangement chamber (drive member arrangement chamber)  15   j  of the upper wall  15   e . Hence, the connection face  15   h  can be easily machined. 
   With reference again to  FIG. 4 , the mounting face  15   i  of the exhaust pipe  22   a  is located at a position along the lower wall  15   g  of the cylinder head  15 , which position is nearly as high as the portion  15   e ′, which corresponds to the cam chain arrangement chamber  15   j . Thus, the cylinder body  14  and the cylinder head  15  extend further downward than the mounting face  15   i  of the exhaust pipe  22   a  and the exhaust pipe  22   a  benefits from increased road clearance such that the exhaust pipe  22   a  does not have to be greatly downsized to fit within the region defined between the engine and a suitable level of road clearance. 
   With reference now to  FIGS. 7 and 8 , another embodiment is shown that is arranged and configured in accordance with certain features, aspects and advantages of the present invention. The same reference symbols as those in  FIGS. 1 to 6  denote the same or corresponding parts. 
   In the arrangement described above, the cylinder bore  14   a  preferably is formed by the cylinder body  14  without the insertion of a cylinder liner. In the arrangement shown in  FIGS. 7 and 8 , for example, a cylinder liner  14   c  can be inserted into the cylinder body  14 . The cylinder liner  14   c  can be formed of any suitable material and can be inserted in any suitable manner. In one arrangement, the cylinder liner  14   c  is formed of cast iron and is pressed into the cylinder body  14 . In such configurations, the inner peripheral surface of the cylinder liner  14   c  forms the cylinder bore  14   a.    
   With reference to  FIG. 7 , a recessed portion  14   b  preferably is defined within the liner  14   c . The recessed portion  14   b  aids in reducing the likelihood of the connecting rod  18  contacting the cylinder bore  14   a . In one particularly preferred arrangement, the recessed portion  14   b  is formed in the shape of the connecting rod. Desirably, the recessed portion  14   b  is positioned only on the end of the cylinder liner  14   c  closest to the crankshaft. More desirably, the recessed portion  14   b  is positioned on the portion of the cylinder liner  14   c  that on the same side as the crankshaft axis of a plane P 1  that (1) extends along the cylinder axis B and (2) is parallel to the crankshaft axis. Even more preferably, the recessed portion  14   b  is intersected by a second plane P 2  that extends generally normal to the first plane P 1  and that intersects the cylinder axis B. 
   This recessed portion  14   b  preferably is sized and configured to reduce the likelihood of interference between the connecting rod  18  and the cylinder bore  14   a  while the length of the connecting rod  18  can be minimized even though the cylinder axis B is offset generally vertically downward. The recessed portion  14   b  advantageously can be formed in such a way as to have a width larger than a radial thickness of the connecting rod  18  and smaller than the width of the skirt portion  17   a  of the piston  17 . More preferably, the distance from the top of the piston at top dead center to the bottom of the skirt portion  17   a  of the piston  17  in bottom dead center is less than the distance from the top of the piston in top dead center to the forwardmost end of the recessed portion  14   b.    
   With provision of the recessed portion  14   b , movement of the connecting rod  18  can be accommodated by the sidewall of the cylinder bore and the length of the connection rode does not need to be elongated to avoid contact with the cylinder bore. Thus, the crankshaft can be located fairly closely to the cylinder body even though the cylinder body is offset from the axis of rotation of the crankshaft. Such an arrangement provides a compact engine in the fore and aft direction even with the vertical offset. Further, because the recessed portion  14   b  is formed only in a portion of the cylinder wall (e.g., the upper portion in  FIG. 8 ), the cylinder liner  14   c  does not need to have an unnecessary material removed therefrom. That is, depending on the amount of offset of the cylinder body  14 , a portion (lower portion in  FIG. 8 ) opposite to the crankshaft axis  12   a  of the cylinder bore  14   a  generally would not interfere with movement of the connecting rod  18  and this portion would not require a recessed portion. While such a recessed portion  14   b  could be formed on both sides or completely around the sleeve, not forming such recessed portions decreases the amount of labor involved in manufacturing the engine. Moreover, the recessed portion  14   b  also can be formed in the engine shown in  FIGS. 1–6 , if desired. 
   Although the present invention has been described in terms of a certain preferred embodiments, other embodiments apparent to those of ordinary skill in the art also are within the scope of this invention. Thus, various changes and modifications may be made without departing from the spirit and scope of the invention. For instance, various components may be repositioned as desired. Moreover, not all of the features, aspects and advantages are necessarily required to practice the present invention. Accordingly, the scope of the present invention is intended to be defined only by the claims that follow.