Patent Publication Number: US-6904883-B2

Title: Modular internal combustion engines

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. patent application Ser. No. 10/409,262 entitled INTERNAL COMBUSTION ENGINE, filed on Apr. 8, 2003, which claims the benefit under Title 35, U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 60/372,560, entitled INTERNAL COMBUSTION ENGINE, filed on Apr. 15, 2002, and U.S. Provisional Patent Application Ser. No. 60/402,841, entitled INTERNAL COMBUSTION ENGINE, filed on Aug. 12, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to small internal combustion engines, which are used in a variety of applications, such as lawnmowers, lawn and garden tractors, other small working implements such as snow throwers and generators, or in sport vehicles. 
   2. Description of the Related Art 
   Small internal combustion engines typically include one or two engine cylinders. Single cylinder engines generally have a valve train of the side valve (“L-head”), overhead cam (“OHC”) or overhead valve (“OHV”) type, and are typically contained within a pair of castings. A first casting may include, for example, the engine cylinder, a portion of the crankcase, and optionally a cylinder head integrally formed with the engine cylinder. A second casting may include a crankcase cover which is attached to the crankcase portion of the first casting to define the enclosed crankcase of the engine. The crankshaft may be disposed in either a horizontal or a vertical orientation, and may be journalled in full bearings, one defined in each crankcase casting, or alternatively, in split bearings, wherein each crankcase casting defines one-half of each of the crankshaft bearings. 
   Twin cylinder engines generally have valve trains of the overhead cam (“OHC”) or overhead valve (“OHV”) type, and are typically contained within a first casting which includes the engine cylinders and a portion of the crankcase. A second casting typically includes a crankcase cover which is attached to the crankcase portion of the first casting to define the enclosed crankcase of the engine. The crankshaft may be disposed in either a horizontal or a vertical orientation, and may be journalled in full bearings, one defined in each crankcase casting, or alternatively, in split bearings, wherein each crankcase casting defines one-half of each of the crankshaft bearings. 
   A disadvantage with existing engine designs is that the castings or housing portions which contain known single and twin cylinder engines have a specific construction which is unique to each of the single and twin cylinder engines. For example, a casting which includes a cylinder and a portion of a crankcase of a vertical crankshaft, single cylinder engine can only be used with that particular vertical crankshaft, single cylinder engine. Although certain minor engine components, such as valves, valve springs, carburetors, etc., might possibly be used in a number of different engines, interchangeability of major engine housing components, such as castings or other housing components, between different types of single and/or twin cylinder engines is not possible. 
   Further, in OHC engines, a camshaft located within the cylinder head of the engine is typically driven with a belt connecting a drive pulley on the crankshaft with a driven pulley on the camshaft. In these engines, assembling the belt to the drive and the driven pulleys can be difficult during the manufacturing process. 
   What is needed is a small internal combustion engine which is an improvement over the foregoing. 
   SUMMARY OF THE INVENTION 
   The present invention provides a line of small internal combustion engines, including twin cylinder engines and single cylinder engines. The engines each include a crankcase, and one or more cylinder members attached to the crankcase, the cylinder members being separate components from the crankcase. A number of different crankcases are provided for various types of single and two cylinder engines, the crankcases having common mounting structure to which the cylinder members may be attached. Thus, the manner in which the cylinder members are attached to the crankcases is the same for each of the different types of crankcases. Two different types of cylinder members are provided, one having a side valve or “L-head” valve train, and the other having an overhead cam (“OHV”) valve train. The cylinder members are therefore modular components which may be selectively used in a variety of different types of engines. 
   The crankshafts of each of the engines may be disposed in either a horizontal orientation or a in vertical orientation to suit the particular application in which the engines are used. In the V-twin engines disclosed herein, the crankcase includes a pair of cylinder members mounted to mounting surfaces of the crankcase at an angle with respect to one another to define a V-space therebetween, and a pair of cylinder heads mounted to the cylinder members. Alternatively, the cylinder members may each include integral cylinder heads. In the single cylinder engines disclosed herein, the crankcase includes a single mounting surface to which a single cylinder member is attached. 
   The cylinder members are modular components, to which components of the valve train may be pre-assembled before the cylinder members are attached to the crankcase, thereby facilitating easier final assembly of the engines. In addition, the same cylinder members may be used in both twin cylinder engines and in single cylinder engines. 
   In one embodiment, the engine valve train is configured as a side valve or “L-head” type valve train, in which intake and exhaust valves are carried each cylinder member. A cylinder head is attached to each cylinder member, with each cylinder member and cylinder head defining a combustion chamber therebetween. 
   In another embodiment, the engine valve train is configured as an overhead valve (“OHV”) valve train, in which push rods are carried in each cylinder member for actuating rocker arms and intake and exhaust valves which are mounted in the cylinder head. 
   In the twin cylinder engines, the cylinder members may be mounted to the crankcase in a manner in which the cylinder members are disposed at an angle, such as a 90° angle, with respect to one another to thereby define a V-space therebetween. The cylinder members each include a cam gear and cam lobe assembly and, when the cylinder members are attached to the crankcase, at least a portion of the cam gears of the cam gear and lobe assemblies extend into the crankcase for driving engagement with a drive gear mounted on the crankshaft. Alternatively, the cylinder members may be mounted to opposite sides of the crankcase to provide a twin cylinder opposed engine. 
   In the twin cylinder engines, one cam gear and lobe assembly is disposed in a first orientation, and the other cam gear and lobe assembly is disposed in an orientation which is rotated 180° with respect to the orientation of the first cam gear and lobe assembly. In this manner, the lobe(s) of the first cam gear and lobe assembly face in a first direction, and the lobe(s) of the second cam gear and lobe assembly face in an opposite direction. With the foregoing construction, space in the crankcase is conserved, and the cam gears may each be driven from a single, relatively thinly profiled drive gear which is mounted to the crankshaft. Additionally, the foregoing construction conserves space within the crankcase by compensating for the “stagger area” which is necessitated in V-twin engines by the connecting rods of the two cylinders positioned adjacent to one another on the crank pin of the crankshaft. 
   The cam lobe(s) of each of the cam gear and lobe assemblies respectively actuate a pair of lifters pivotally mounted in each of the cylinder members. When the cylinder members are configured for a side valve or “L-head” engine, the cylinder members include intake and exhaust valves which are directly actuated by the lifters. When the cylinder members are configured for an OHV engine, the cylinder members include push rods which are actuated by the lifters, the push rods in turn actuating a valve assembly in the cylinder head, which includes rocker arms and intake and exhaust valves. 
   Further, the cylinder members may also be used in single cylinder engines to form side valve or “L-head” horizontal or vertical crankshaft engines, or OHV horizontal or vertical crankshaft engines. In this manner, the cylinder members are modular components which may be used in either twin cylinder engines or in single cylinder engines, thereby reducing the number of total components which are needed to produce a line of single cylinder and two cylinder engines, as well as the costs associated with manufacturing the line of single and twin cylinder engines. 
   In particular, the cylinder members which are configured for a side valve or “L-head” valve train and the cylinder members which are configured for an OHV valve train each include identical cam gear and lobe assemblies and identical lifter assemblies. In each configuration, the cam gears extend at least partially into the crankcase for driving engagement with a drive gear mounted to the crankshaft. Thus, the valve train for each of the foregoing configurations is identical between the crankshaft and the lifters, permitting the two types of cylinder members to be assembled to a crankcase in the same manner, and permitting the same crankcase to be used with either type of cylinder member. 
   In one form thereof, the present invention provides a line of internal combustion engines, including a plurality of first engines, each first engine including a first crankcase and at least one cylinder member connected to the first crankcase, each cylinder member and each first crankcase being separate components; and a plurality of second engines, each second engine including a second crankcase and at least one cylinder member connected to the second crankcase, each cylinder member and each second crankcase being separate components, the first and second crankcases different from one another; each of the first and second crankcases including at least one cylinder mount to which a respective cylinder member is connected, the cylinder mounts common between the first and second crankcases whereby the cylinder members are interchangeably connectable to the first and second crankcases in the same manner; and a valve train assembly respectively supported entirely by each cylinder member, a first portion of the valve train assembly disposed within a respective cylinder member and a second portion of the valve train assembly disposed respectively within one of the first and second crankcases. 
   In another form thereof, the present invention provides a line of internal combustion engines, including a plurality of first engines, each first engine including a crankcase and at least one first cylinder member connected to the crankcase, the crankcase and the first cylinder member being separate components, the first cylinder member housing a valve train of a first type; and a plurality of second engines, each second engine including a crankcase and at least one second cylinder member connected to the crankcase, the crankcase and the second cylinder member being separate components, the second cylinder member housing a valve train of second type; each of the crankcases including at least one cylinder mount to which a respective cylinder member is connected, the cylinder mounts common between the crankcases whereby the cylinder members are interchangeably connectable to the crankcases in the same manner. 
   In a further form thereof, the present invention provides a method of assembling an internal combustion engine, including the steps of: providing a plurality of a first type of crankcases and providing a plurality of a second type of crankcases, the first and second types of crankcases differing from one another, all of the first and second types of crankcases having common cylinder mounting structure including an opening in a wall of each crankcase; selecting a crankcase from the plurality of a first type of crankcases; providing a cylinder member having a valve train assembly, at least a portion of the valve train assembly extending externally of the cylinder member; attaching the cylinder member to the mounting structure of the selected crankcase of the first type such that the portion of the valve train assembly extends through the opening in the wall of the selected crankcase; selecting a crankcase from the plurality of a second type of crankcases; providing a cylinder member having a valve train assembly, at least a portion of the valve train assembly extending externally of the cylinder member; and attaching the cylinder member to the mounting structure of the selected crankcase of the second type such that the portion of the valve train assembly extends through the opening in the wall of the selected crankcase. 
   In another form thereof, the present invention provides a method of assembling an internal combustion engine, including the steps of: providing a plurality of a first type of cylinder members and providing a plurality of a second type of cylinder members, the first and second types of cylinder members having valve trains of a different type; selecting a cylinder member from the plurality of the first type of cylinder members; providing a first crankcase; attaching the selected cylinder member of the first type to the first crankcase; selecting a cylinder member from the plurality of the second type of cylinder members; providing a second crankcase; and attaching the selected cylinder member of the second type to the second crankcase. 
   In another form thereof, the present invention provides a method of assembling an internal combustion engine, including the steps of: providing a plurality of a first type of crankcase and providing a plurality of a second type of crankcase, the first and second types of crankcases differing from one another, all of the first and second types of crankcases having common cylinder mounting structure including an opening in a wall of each crankcase; selecting a crankcase from the plurality of the first type of crankcases; providing a plurality of a first type of cylinder members and providing a plurality of a second type of cylinder members, the first and second types of cylinder members having valve trains of a different type; selecting a cylinder member from the plurality of the first type of cylinder members; attaching the selected cylinder member from the first plurality of cylinder members to the selected crankcase of the first plurality of crankcases; selecting a crankcase from the plurality of the second type of crankcases; selecting a cylinder member from the plurality of the second type of cylinder members; and attaching the selected cylinder member from the second plurality of cylinder members to the selected crankcase of the second plurality of crankcases. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings wherein: 
       FIG. 1  is a front perspective view of a horizontal crankshaft, V-twin engine according to the present invention, the engine having a side valve or “L-head” valve train; 
       FIG. 2  is a front view of the engine of  FIG. 1 ; 
       FIG. 3  is a right side view of the engine of  FIG. 1 ; 
       FIG. 4  is a left side view of the engine of  FIG. 1 ; 
       FIG. 5  is a top view of the engine of  FIG. 1 ; 
       FIG. 6  is a front elevational view of the engine of  FIG. 1 , with the shroud removed to show the crankcase, a pair of cylinder members mounted to the crankcase, an intake assembly associated with the cylinder members, and a flywheel mounted to the crankshaft; 
       FIG. 7  is a front elevational view of the engine of  FIG. 6 , in which the crankcase cover and flywheel have been removed, the cylinder members and a portion of the crankcase in section to show the valve train of the engine; 
       FIG. 8  is a sectional view taken along line  8 — 8  of  FIG. 7 ; 
       FIG. 9  is an exploded view of a cylinder member of the engine, showing the components of the valve train and a cylinder head; 
       FIG. 10  is an assembled view of the cylinder member of  FIG. 9 ; 
       FIG. 11  is a sectional view through the cylinder member of  FIG. 10 , taken along line  11 — 11  of  FIG. 10 ; 
       FIG. 12  is a perspective view of components of the valve train within the cylinder member of  FIGS. 9-11 ; 
       FIG. 13  is an exploded view of the crankcase, crankcase cover, and cylinder members of the engine of  FIGS. 1-7 , showing the attachment of the crankcase cover and cylinder members to the crankcase, and further showing an exploded view of the breather assembly of one of the cylinder members; 
       FIG. 14  is a partial perspective view of the engine of  FIGS. 1-7  in a vertical crankshaft orientation, showing a breather cover attached to a cylinder member, the cylinder cover including a breather hose fitting and ignition module supports; 
       FIG. 15  is a perspective view of a vertical crankshaft, V-twin engine according to the present invention, the engine including an overhead valve (“OHV”) valve train; 
       FIG. 16  is a front elevational view of the engine of  FIG. 15 ; 
       FIG. 17  is a top view of the engine of  FIGS. 15 and 16 ; 
       FIG. 18  is a bottom view of the engine of  FIGS. 15-17 ; 
       FIG. 19  is a rear perspective view of the engine of  FIGS. 15-18 , with a portion of the crankcase, crankcase cover, cylinder member, cylinder head, and cylinder hear cover cut away to show valve train components of engine; 
       FIG. 20  is a top elevational view of the engine of  FIGS. 15-19 , with the crankcase cover removed and with the cylinder members and cylinder heads in section to show the valve train of the engine; 
       FIG. 21  is an exploded view of a cylinder member and cylinder head assembly of the engine of  FIGS. 15-21 ; 
       FIG. 22  is a first perspective, assembled view of the cylinder member and cylinder head assembly of  FIG. 21 ; 
       FIG. 23  is a second perspective, assembled view of the cylinder member and cylinder head assembly of  FIG. 21 ; 
       FIG. 24  is a partial sectional view of the cylinder member and cylinder head assembly of  FIG. 21 ; 
       FIG. 25  is a sectional view of a twin cylinder opposed engine including the cylinder members of the engine of  FIGS. 1-14 ; 
       FIG. 26  is a sectional view of a single cylinder, vertical crankshaft engine including a cylinder member of the engine of  FIGS. 1-14 ; 
       FIG. 27  is a sectional view of a single cylinder, horizontal crankshaft engine including a cylinder member of the engine of  FIGS. 1-14 , the engine having a vertical profile; 
       FIG. 28  is a sectional view of a single cylinder, horizontal crankshaft engine including a cylinder member of the engine of  FIGS. 1-14 , the engine having a slant profile; 
       FIG. 29  is a schematic view illustrating a number of different types of crankcases and a pair of different cylinder members, each of the cylinder members attachable to each of the crankcases to form a number of different types of engines; and 
       FIG. 30  is a perspective view illustrating the common mounting structure between each of the cylinder members of FIG.  29  and each of the crankcases of FIG.  29 . 
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
   

   DETAILED DESCRIPTION 
   Referring to  FIGS. 1-7 , a first internal combustion engine  50  is shown as a horizontal crankshaft, V-twin engine having a side valve or “L-head” valve train, as discussed in detail below. However, engine  50  may, with minor modifications, also be configured as a vertical crankshaft, V-twin engine having a side valve or “L-head” valve train, as shown in FIG.  14 . Also described below is engine  300 , shown in  FIGS. 15-24  which is similar to engine  50 , and which may be configured as a horizontal or vertical crankshaft V-twin engine having an overhead valve (“OHV”) valve train. Further, the cylinder members of engines  50  or  300  may also be used in a twin cylinder opposed engine such as engine  400  shown in FIG.  25 . Still further, a cylinder member of engines  50  or  300  may be used in a vertical or a horizontal crankshaft single cylinder engine, such as engines  500 ,  600 , and shown in  FIGS. 26 ,  27 , and  28 , respectively. 
   Referring first to  FIGS. 1 ,  6 , and  7 , engine  50  includes crankcase  52 , having base portion  54  for connection of the engine to, or for supporting the engine on, an implement (not shown) with which engine  50  is used, such as a snow thrower, generator, lawn tractor, small sport vehicle, or other small working implement or vehicle. Referring to  FIGS. 8 and 13 , crankcase  52  includes first crank bearing  56  in a rear wall thereof, in which one end of crankshaft  58  is journalled for rotation. Crankcase cover  57 , shown in  FIGS. 8 ,  13 , and  14 , is attached to crankcase  52  with suitable fasteners  59  ( FIG. 13 ) to enclose crankcase  52  and includes second crank bearing  60 , disposed opposite first crank bearing  56 , in which the opposite end of crankshaft  58  is journalled for rotation. Each of first and second crank bearings  56 ,  60  is a full bearing provided in crankcase  52  and in crankcase cover  57 , respectively. 
   Referring to  FIG. 7 , crankcase  52  includes oil sump  62  therein, in which a quantity of lubricating oil is contained. Oil may be filled into crankcase  52  through oil fill opening  64  ( FIGS. 6 and 13 ) formed integrally with crankcase  52 , to which oil fill conduit  66  may be attached. As shown in  FIG. 6 , oil fill conduit  66  is a tubular member formed of a suitable plastic material, and includes a removable oil fill cap  68 . Referring to  FIG. 7 , a plurality of reinforced portions or bosses  70  are formed integrally within crankcase  52 , which may be used as attachment points for attaching an output component to engine  50 , such as a transmission or a working device, for example. 
   Referring to  FIGS. 7 and 13 , crankcase  52  includes a pair of mounting surfaces  72   a  and  72   b  for attachment thereto of cylinder members  74   a  and  74   b,  respectively. Mounting surfaces  72   a  and  72   b  are shown disposed at a 90° angle with respect to one another, thereby positioning cylinder members  74   a  and  74   b  at a 90° angle with respect to one another. Alternatively, the angle between mounting surfaces  72   a  and  72   b,  and in turn the angle between cylinder members  74   a  and  74   b,  may be varied as desired. Mounting surfaces  72   a  and  72   b  include openings  76  therein into which certain valve train components of cylinder members  74   a  and  74   b  are inserted when cylinder members  74   a  and  74   b  are attached to mounting surfaces  72   a  and  72   b  of crankcase  52 , as described below. Mounting surfaces  72   a  and  72   b  may be reinforced, for example, by casting same to a thickness greater than that of the remainder of crankcase  52 , by insert molding one or more plates in crankcase  52  around openings  76  which is made from a material harder than that of crankcase  52 , or by securing such plate(s) to mounting surfaces  74   a  and  74   b  around openings  76  after crankcase  52  is cast. 
   Referring to  FIG. 6 , crankshaft  58  includes flywheel  78  mounted to an end thereof which extends externally of crankcase cover  57 . Flywheel  78  includes permanent magnet  80  disposed between fins  82  thereof. Electronic ignition modules  84  are connected one to each of cylinder members  74   a  and  74   b  as described below, and are positioned closely adjacent the outer periphery of flywheel  78  adjacent permanent magnet  80 . Electronic ignition modules  84  are operably connected to spark plugs  86  of engine  50  by leads  88 , shown in  FIGS. 1-4 , such that rotation of flywheel  78  causes permanent magnet  80  to pass near each electronic ignition module  84  to induce an ignition spark in each spark plug  86  in a conventional manner. Additionally, a starter (not shown) is attached to crankcase  52 , and engages flywheel  78  to rotate crankshaft  58  for starting engine  50 . 
   Referring to  FIGS. 8 and 9 , cylinder members  74   a  and  74   b  each generally include a cylinder bore  90  for slidable receipt of a piston  91  therein, as well as mounting surfaces  92  for attachment to mounting surfaces  72   a  and  72   b  of crankcase  52 , and upper attachment faces  94  for attachment thereto of cylinder heads  96 . Alternatively, cylinder heads  96  may be integrally formed with cylinder members  74   a  and  74   b  each include intake port  98  and exhaust port  100 , with intake port  98  formed in a first side of each cylinder member  74   a  and  74   b , and exhaust port  100  formed in a second side of each cylinder member  74   a  and  74   b  opposite the first side in which intake port  98  is formed. 
   As shown in  FIGS. 6 and 7 , a V-space  102  is defined between cylinder members  74   a  and  74   b.  Referring to  FIG. 7 , the cylinder members  74   a  and  74   b  are mounted to crankcase  52  such that intake ports  98  of each of cylinder members  74   a  and  74   b  are disposed adjacent or within, the V-space  102 , and the exhaust ports  100  of each of cylinder members  74   a  and  74   b  are disposed on a side of cylinder members  74   a  and  74   b  which is opposite intake ports  96  and which therefore faces outwardly from V-space  102 . The positioning of intake ports  98  and exhaust ports  100  which is provided by the configuration of cylinder members  74   a  and  74   b  advantageously places intake ports  98  close to one another, thus allowing intake assembly  104  of engine  50  to be disposed within V-space  102 , while minimizing the length of intake pipes  106  of intake assembly  104 . Additionally, the positioning of exhaust ports  100  outwardly of V-space  102  and to the sides of engine  50  readily exposes same to cooling air from flywheel  78 , and further, the accumulation of an excessive amount of heat within V-space  102  is avoided by positioning exhaust ports  100  to the sides of engine  50  where the heat therefrom may be readily dissipated. 
   Referring to  FIGS. 9 ,  10 , and  13 , cylinder members  74   a  and  74   b  also each include rectangular-shaped openings  108  therein which provide access to the interior of cylinder members  74   a  and  74   b , including the components of valve train  110  of engine  50 , as described below. Openings  108  are covered by cylinder member covers  112   a,    112   b,  the details of which are discussed below. Cylinder member covers  112   a,    112   b  include integral posts  114 , best shown in  FIGS. 9 ,  13  and  14 , to which electronic ignition modules  84  ( FIG. 6 ) are attached to support and position electronic ignition modules  84  adjacent the peripheral edge of flyweight  78  adjacent permanent magnet  80 . 
   Referring to  FIGS. 6 and 7 , intake assembly  104  includes carburetor  116  having fuel inlet  118 , fuel bowl  120 , and throat  122  extending therethrough in which throttle and choke valves (not shown) are rotatably mounted. Intake pipes  106  extend between an outlet end (not shown) of carburetor  116  and intake ports  98  of cylinder members  74   b  and  74   b . Carburetor  116  also includes mounting flange  124  on its inlet side, shown in  FIG. 7 , for attachment of air cleaner plate  126  thereto. Air cleaner plate  126  cooperates with shroud  128  and air cleaner cover  130 , shown in  FIGS. 1 and 2 , to define an enclosed air cleaner cavity in which an air cleaner or filter element (not shown) is positioned for filtering debris from intake air before same enters carburetor  116 . 
   Further details regarding the air intake system of the engines disclosed herein are set forth in U.S. patent application Ser. No. 10/408,882, entitled AIR CLEANER ASSEMBLY FOR INTERNAL COMBUSTION ENGINES, filed on Apr. 8, 2003 assigned to the assignee of the present invention, the disclosure of which is expressly incorporated herein by reference. Also, further details regarding the operation of carburetor  116 , including the choke and throttle controls thereof, as well as the operation of other user interfaces of engine  50 , are set forth in U.S. patent application Ser. No. 10/409,202, entitled ENGINE CONTROL SYSTEM, filed on Apr. 8, 2003 assigned to the assignee of the present invention, the disclosure of which is expressly incorporated herein by reference. 
   Referring to  FIGS. 1-5 , shroud  126  is attached to crankcase  52  and cylinder members  74   a  and  74   b,  and substantially covers the front side of crankcase  52 , including flywheel  78 , and also the front side of cylinder members  74   a  and  74   b.  Air inlet screen  132  is attached to shroud, and may cover a recoil starter mechanism (not shown) attached to crankshaft  52  in applications where engine  50  does not include an electric starter motor. Air inlet screen  132  includes a plurality of louvers  134  therein into which intake air may be drawn by flywheel  78  into the area between crankcase  52  and shroud  128 , which intake air is directed by shroud  128  to the air cleaner cavity beneath air cleaner cover  130  for combustion within engine  50 . Also, air may be directed by shroud  128  and cylinder wraps  136  around cylinder members  74   a  and  74   b  for cooling same during running of engine  50 . 
   Cylinder wraps  136 , shown in  FIGS. 1-4 ,  6 , and  7 , may be made of a relatively thin sheet metal, for example, and are attached to crankcase  52  and cylinder members  74   a  and  74   b  for directing cooling air closely around cylinder members  74   a  and  74   b.  Brackets  138  are attached to cylinder wraps  136  adjacent the upper ends of cylinder members  74   a  and  74   b,  and fuel tank  140  is in turn attached to brackets  140  with suitable fasteners. Fuel tank  140  has a broad, relatively thin horizontal profile, and is mounted to the upper end of engine  50  above the upper ends of cylinder members  74   a  and  74   b.  Advantageously, as shown in  FIGS. 7 and 8 , because brackets  138  are respectively disposed above cylinder members  74   a  and  74   b  and are spaced relatively far from one another, the weight of fuel tank  140  is distributed over a relatively large area of engine  50 . Fuel tank  140  includes a filler neck (not visible) to which fuel tank cap  142  is attached, which may be removed for filling fuel into fuel tank  140 . 
   Referring generally to  FIGS. 9-12 , the valve train  110  of engine  50  is shown, which is configured as a side valve or “L-head” valve train. Drive gear  150  is mounted to crankshaft  58 , and includes teeth  152  which mesh with teeth  154  of cam gears  156  to drive cam gears  156  at one-half the speed of crankshaft  58 . Cam gears  156  are rotatably mounted on shafts  158  which are connected to cylinder members  74   a  and  74   b  in the manner described below. Cam gears  156  also each include at least one cam lobe  160  which may be integrally formed with cam gears  156  to thereby form cam gear and lobe assemblies  162 . For example, cam gear and lobe assemblies  162  may be formed as an integral piece of a molded rigid plastic material. Alternatively, cam gears  156  and cam lobes  160  may be formed as separate components which are secured to one another in a suitable manner. 
   Referring to  FIG. 8 , pistons  91  of each cylinder member  74   a  and  74   b  are slidably disposed within cylinder bores  90 . Connecting rods  93  are each attached at one end thereof to a piston  91  by wrist pin  95 , and are attached at an opposite end thereof to crank pin  99  by split cap  97 . Connecting rods  93  are staggered along crank pin  99  of crankshaft  58 , and therefore cylinder bores  90  within cylinder members  74   a  and  74   b  are also staggered with respect to one another, as may be seen in FIG.  8 . 
   To conserve space within crankcase  52 , as shown in  FIGS. 7 and 8 , it may be seen that a first cam gear and lobe assembly  162   a  is disposed in a first orientation, and a second cam gear and lobe assembly  162   b  is disposed in an orientation which is rotated 180° with respect to the orientation of the first cam gear and lobe assembly  162   a.  Alternatively stated, a first cam gear and lobe assembly  162   a  faces in a first direction (i.e., toward the rear of engine  50 ) and a second cam gear and lobe assembly  162   b  faces in a second direction opposite the first direction (i.e., toward the front of engine  50 ). Correspondingly, the lobe(s)  160  of the first cam gear and lobe assembly  162   a  face in a first direction (i.e., toward the rear of engine  50 ), and the lobe(s)  160  of the second cam gear and lobe assembly  162   b  face in an opposite direction (i.e., toward the front of engine  50 ). As may be seen from  FIG. 8 , with the foregoing construction, space in crankcase  52  is conserved even though cylinder bores  90  and connecting rods  93  are staggered with respect to one another, and cam gears  156  may each be driven from a single, relatively thinly-profiled drive gear  150  mounted to crankshaft  58 . 
   Referring to  FIGS. 9-12 , rotation of cam gears  156  causes cam lobes  160  to periodically actuate lifters  164 , which are pivotally mounted upon off-center adjusters  166 , which are in turn secured to cylinder members  74   a  and  74   b  by mounting bolts  168 . As shown in  FIGS. 11 and 12 , lifters  164  each include follower portion  170  in engagement with cam lobes  160 , and actuator portion  172  in engagement with intake and exhaust valves  174  and  176 , respectively, which are slidably carried within valve guides  178  of cylinder members  74   a  and  74   b.  Within each cylinder member  74   a  and  74   b,  intake and exhaust valves  174  and  176  are disposed radially adjacent cylinder bore  90 . Intake and exhaust valves  174  and  176  are seated within valve seats  180  which may be integrally cast into cylinder members  74   a  and  74   b.  Alternatively, valve seats  180  may be formed as separate components which are press-fitted into cylinder members  74   a  and  74   b,  as shown in  FIGS. 9 and 11 . Valve springs  182  are coiled about each of intake and exhaust valves  174  and  176  under compression between spring seats  184  ( FIG. 11  ) of cylinder members  74   a  and  74   b  and valve keepers  186 , and normally bias intake and exhaust valves  174  and  176  to a closed position wherein intake and exhaust valves  174  and  176  are seated against valve seats  180 . 
   Referring to  FIGS. 9 and 11 , cylinder heads  96  include depressions  188  which, together with the upper ends of cylinder bores  90  of cylinder members  74   a  and  74   b,  define combustion chambers  190  in which the spark gap end of spark plugs  86  project. Spark plugs  86  are actuated by the ignition system of engine  50  for igniting a compressed air/fuel mixture within combustion chambers  190  to drive engine  50  according to a conventional four-stroke cycle, in which valve train  110  of engine  50  is operable as described above to periodically introduce an air/fuel combustion mixture into combustion chambers  190  and to allow combustion products to evacuate combustion chambers  190  after combustion therein. 
   As shown in  FIG. 7 , one of cam gears  156  may drive governor mechanism  192 , which may be rotatably supported upon stub shaft  193  connected to either crankcase  52  or to crankcase cover  57 . Alternatively, governor mechanism  192  may be supported upon a shaft journalled in bearings provided in crankcase  52  and/or in crankcase cover  57 . Governor mechanism  192  is operably connected to carburetor  116  of intake assembly  104  to regulate the mass fuel/air intake of engine  50  in response to engine speed and engine load. 
   During running of engine  50 , the moving parts within crankcase  52 , such as crankshaft  58 , oil slingers or dippers (not shown) attached to the connecting rods  93  of the engine, and governor mechanism  192 , create an oil mist within crankcase  52  which, under the pressure fluctuations generated by the pistons reciprocating within cylinder members  74   a  and  74   b,  is forced into cylinder members  74   a  and  74   b  to lubricate valve train  110 , including cam gears  156 , lifters  164 , and intake and exhaust valves  174  and  176 . Upon condensation, the oil may drip back into crankcase  52  from cylinder members  74   a  and  74   b.    
   Additionally, one of the cylinder members  74   a  and  74   b,  such as cylinder member  74   b,  for example, includes breather assembly  194 , shown in  FIG. 13 , for venting blow-by gasses from crankcase  52 . Breather assembly  194  includes gasket  196  made of a flexible, compressible material such as rubber; breather plate  198  having valve seat/opening  200  and drain holes  202 ; flapper valve  204  made of a flexible material such as spring steel; valve retainer  206  made of a rigid material; filter media  208  made of a porous material; breather plate cover  210  made of a flexible, compressible material such as rubber and having opening  212  therein; and cylinder member cover  112   b  having hose fitting  214 . Bolts  216  pass successively through apertures in cylinder cover member  112   b,  breather plate cover  210 , breather plate  198 , gasket  196 , and into apertures in cylinder member  74   b  to thereby cover opening  108  of cylinder member  74   b  and to assemble breather assembly  194  to cylinder member  74   b.  As shown in  FIG. 13 , breather assembly  194  is attached only to cylinder member  74   b,  and Opening  108  of cylinder member  74   b  is covered by gasket  196  and cylinder cover member  112   a  attached thereto by bolts  216 . Alternatively, if desired, both cylinder members  74   a  and  74   b  may include breather assemblies  194 . 
   In operation, blow-by gasses, which pass around the pistons  91  from combustion chambers  190  into crankcase  52  during running of engine  50 , tend to accumulate within crankcase  52  and increase the pressure therein. When such pressure increases to a certain level, the blow-by gas pressure causes flapper valve  204  to flex against the bias force of valve retainer  206  away from valve seat/opening in breather plate  198  to vent the blow-by gasses from the interior of cylinder member  74   b  into a chamber defined between breather plate  198  and breather plate cover  210 . In this chamber, oil separates from the blow-by gasses by gravity and condensation, and drips back into crankcase  52  through drain holes  202  in breather plate  198 . Also, oil may be trapped within filter media  208 . The blow-by gasses then pass through opening  212  in breather plate cover  210  and thereafter may exit cylinder member cover  112   b  through hose fitting  214 . A breather conduit  215 , shown in  FIG. 6 , is connected between hose fitting  214  of cylinder member cover  112   b  to convey the blow-by gasses to the air filter cavity of engine  50  for recycling. 
   The assembly of engine  50  will now be described. Notably, engine  50  may be assembled in a manner in which cylinder members  74   a  and  74   b,  and the components of valve train  110  which are attached to cylinder members  74   a  and  74   b,  are first assembled as packaged units and then subsequently attached to crankcase  52 . For example, valve seats  180  may be press-fit into cylinder members  74   a  and  74   b  , as shown in  FIG. 9 , and intake and exhaust valves  174  and  176  may then be assembled to cylinder members  74   a  and  74   b.  As shown in  FIG. 9 , a plurality of bolts  218  may be inserted through apertures  220  in cylinder heads  96  and into holes (not shown) in cylinder members  74   a  and  74   b  to attach cylinder heads  96  to cylinder members  74   a  and  74   b  at a suitable point in the assembly process. Lifters  164  may then be assembled to off-center adjusters  166 , secured by bolts  168  to cylinder members  74   a  and  74   b.    
   As shown in  FIG. 9 , cam gear and lobe assemblies  162  may be attached to cylinder members  74   a  and  74   b  by first positioning cam gear and lobe assemblies  162  between ears  222   a  and  222   b  projecting from cylinder members  74   a  and  74   b,  followed by inserting shafts  158  through large aperture  224  in ear  222   a,  through the central aperture of cam gear and lobe assemblies  162 , and into small aperture  226  in ear  222   b.    
   After the components of valve train  110  are assembled to cylinder members  74   a  and  74   b  as described above, the clearance of intake and exhaust valves  174  and  176  may be adjusted. In particular, the construction of off-center adjusters  166 , upon which lifters  164  are pivotally mounted, as well as the manner in which the valve clearance or “valve lash” between actuator portions  172  of lifters  164  and their respective intake and exhaust valves  174  and  176  may be adjusted, is described in detail in U.S. patent application Ser. No. 10/262,455, filed on Oct. 1, 2002, entitled VALVE CLEARANCE ADJUSTMENT MECHANISM, assigned to the assignee of the present invention, the disclosure of which is expressly incorporated herein by reference. The foregoing valve clearance or “valve lash” of intake and exhaust valves  174  and  176  may be adjusted either before or after cylinder members  74   a  and  74   b  are attached to crankcase  52 , as described below. 
   Referring to  FIG. 13 , cylinder members  74   a  and  74   b  may be attached to crankcase  52  by inserting cam gear and lobe assemblies  162  of cylinder members  74   a  and  74   b  through openings  76  in mounting surfaces  72   a  and  72   b  of crankcase  52  and positioning cylinder members  74   a  and  74   b  in abutment with mounting surfaces  72   a  and  72   b  of crankcase  52  such that cooperating bores  228  in cylinder members  74   a  and  74   b  are in alignment with bores  230  in mounting surfaces  72   a  and  72   b  of crankcase  52 . In this manner, it may be seen that cam gear and lobe assemblies  162  extend into crankcase  52  for meshing engagement thereof with drive gear  150  of crankshaft  58 , as also shown in FIG.  7 . Thereafter, a plurality of long bolts  232  are inserted through bores  228  in cylinder members  74   a  and  74   b  and into bores  230  in mounting surfaces  72   a  and  72   b  of crankcase  52  to attach cylinder members  74   a  and  74   b  to crankcase  52 . 
   Cylinder heads  96  may be attached to cylinder members  74   a  and  74   b  either before or after cylinder members  74   a  and  74   b  are attached to crankcase  52 . Specifically, as shown in  FIG. 13 , cylinder member  74   a  is attached to crankcase  52  before a cylinder head  96  is attached to cylinder member  74   a . In this manner, a piston  91  and connecting rod  93  assembly (not shown in  FIG. 13 ) may be inserted through cylinder bore  90  and attached to crank pin  99  of crankshaft  58  prior to attachment of the cylinder head  96  to cylinder member  74   a.    
   Alternatively, as shown in  FIG. 13 , cylinder bead  96  is attached to cylinder member  74   b  prior to attachment of cylinder member  74   b  to crankcase  52 . In this manner, a piston  91  and connecting rod  93  assembly (not shown in  FIG. 13 ) may be inserted through cylinder bore  90  of cylinder member  74   b  prior to attachment of cylinder head  96 , and the connecting rod  93  is attached to crank pin  99  of crankshaft  58  after attachment of cylinder member  74   b  to crankcase  52 . 
   After one cylinder member  74   a  or  74   b  is attached to crankcase  52  and the cam and gear assembly  162  thereof is brought into meshing engagement with drive gear  150  on crankshaft  58 , the engine timing is then set in a suitable manner. Then, the other of cylinder member  74   a  or  74   b  is attached to crankcase  52  and the cam and gear assembly  162  thereof is brought into meshing engagement with drive gear  150  on crankshaft  58 . Finally, a plurality of bolts  59  are used to attach crankcase cover  57  to crankcase  52 , with an end of crankshaft  58  journalled in crank bearing  60  of crankcase cover  57 . 
   Referring to  FIGS. 15-24 , engine  300  is shown as a vertical crankshaft, V-twin engine having an overhead valve (“OHV”) valve train, as discussed in detail below. Engine  300  has several components which are identical to engine  15  discussed above, and like reference numerals have been used to identify such components. Engine  300  may, with minor modifications, also be configured as a horizontal crankshaft, V-twin engine. Engine  300  generally includes crankcase  302 , crankcase cover  304 , and a pair of cylinder members  306   a  and  306   b,  which are mounted to crankcase  302  in the same manner as discussed above with respect to engine  50 . Further, engine  300  is assembled in substantially the same manner as engine  50 , except as discussed below. 
   Referring first to  FIG. 19 , crankcase  302  includes bottom wail  308  having first crank bearing  56  therein. Side walls  310  depend upwardly from, and are integrally formed with, base wall  308 . Side walls  310  are relatively elevated, such that crankcase  302  has a relatively deep, tub-like shape, with oil sump  62  entirely carried within crankcase  302 , and crankcase cover  304  enclosing the open upper end of crankcase  302 . The interface between crankcase  302  and crankcase cover  304  is disposed toward the top of engine  300 , and not in the area of oil sump  62  as in known engines, thereby reducing the potential of oil leaks from oil sump  62  at such interface or elsewhere. 
   Crankcase  302  includes an integral mounting flange  312  extending therefrom, which includes a series of apertures  314  through which fasteners (not shown) may be inserted for mounting engine  300  to an implement. As shown in  FIGS. 15 ,  17 , and  18 , side wall  310  of crankcase  302  includes a fitting  316  for screw-threaded attachment of oil filter  318 . Oil fill tube  320 , shown in  FIGS. 15 and 19 , is attached to crankcase cover  304  in a suitable manner, and is in fluid communication with the interior of crankcase  302  for filling oil through oil fill tube  320  into oil sump  62 . Oil fill tube  320  includes removable oil fill cap  68 . 
   Referring to  FIGS. 15 ,  16 , and  19 , flywheel  78  is mounted to an end of crankshaft  58  which extends externally of crankcase cover  304 , and has a plurality of teeth  322  around the outer periphery thereof which may be engaged by a suitable starter mechanism (not shown) to crank engine  300  for starting. The power take off (“PTO”) end of crankshaft  58  extends externally of crankcase  302  therebelow for driving connection to a blade or other working device, for example. Air inlet screen  132  is disposed above flywheel  78 , and is mounted to shroud  128  of engine  300 . Intake air is drawn through air inlet screen  132  by rotation of flywheel  78  during running of engine  300 . 
   As shown in  FIGS. 15-20 , the two cylinder assemblies, which include cylinder members  306   a  and  306   b  and their cylinder heads  324 , define V-space  102  therebetween, and intake assembly  104 , which includes carburetor  116  and intake pipes  106 , is disposed within V-space  102 . Cylinder heads  324  are mounted to the outer ends of cylinder members  306   a  and  306   b,  and enclose the ends of cylinder bores  90  within cylinder members  306   a  and  306   b  to define combustion chambers  190 . Cylinder heads  324  additionally include intake ports  328  and exhaust ports  330 . Intake ports  328  are disposed within a wall of cylinder heads  324  which faces inwardly within V-space  102  for connection of intake pipes  106  to intake ports  328 . Exhaust ports  330  are disposed within a wall of cylinder heads  324  which is spaced approximately 90° from the wall in which intake ports  328  are disposed. As shown in  FIG. 18 , exhaust ports  330  face toward the bottom of engine  300 ; however, the foregoing configuration may be modified. For example, exhaust ports  330  may be disposed in a wall of cylinder heads  324  which is disposed opposite V-space  102 , such that exhaust ports  330  face outwardly toward respective sides of engine  300 . 
   As shown in  FIGS. 21-23 , cylinder members  306   a  and  306   b  each include openings  307 , similar to openings  108  of cylinder members  74   a  and  74   b , through which components of valve train  332 , such as lifters  164  and off-center adjusters  166 , may be accessed. Covers  112   a  and  112   b,  identical to those used with cylinder members  74   a  and  74   b , may be secured to cylinder members  306   a  and  306   b  to cover openings  307  in the same manner as discussed above with respect to engine  50 . 
   Referring to FIGS.  19  and  20 - 24 , valve train  332  of engine  300  is shown. Valve seats  334  are pressed into cylinder heads  324 , or alternatively, may be cast into cylinder heads  324 . Intake and exhaust valves  336  and  338  are reciprocatingly carried in valve guides  339  in cylinder heads  324 . Valve springs  340  are captured between spring seats  342  ( FIGS. 20 and 24 ) and valve keepers  344  to bias intake and exhaust valves  336  and  338  to a normally closed position, in which the heads of intake and exhaust valves  336  and  338  seat against valve seats  334  to close intake and exhaust ports  328  and  330 , respectively, from combustion chamber  190 . Rocker arms  346  are pivotally mounted on a rocker arm shaft  348 , which is inserted through apertures in support hubs  347  within cylinder head  324 , and are operably connected to intake and exhaust valves  336  and  338  and also to push rods  350 . Rockers arms  346  further include lash adjustment screws  343  and nuts  345  for adjusting the clearance or “lash” between rocker arms  346  and the ends of push rods  350 . 
   Push rods  350  extend between lifters  164  and rocker arms  346 , and are reciprocatingly carried both within cylinder members  306   a  and  306   b  and cylinder heads  324 . As shown in  FIGS. 19 ,  21 , and  24 , push rods  350  are disposed radially adjacent cylinder bores  190 . Referring to  FIG. 21 , push rods extend through push rod bores  351  in cylinder members  306   a  and  306   b,  and also extend through push rod sleeves  353  of cylinder heads  324 . Open outer ends  352  of cylinder heads  324  and cylinder head covers  354  cooperate to define rocker boxes  356 , in which rocker arms  346  and other components of valve train  332  are disposed, as shown in  FIGS. 19 ,  21 , and  24 . 
   Notably, valve train  332  of engine  300  is identical to valve train  110  of engine  50  from crankshaft  58  to lifters  164 . In engine  50 , lifters  164  directly engage intake and exhaust valves  174  and  176 , such that engine  50  has a side valve, or “L-head” configuration for valve train  110 . In engine  300 , lifters  164  engage push rods  150  to translate same, which actuates rocker arms  346 , which in turn actuates intake and exhaust valves  336  and  338 , such that engine  300  has a overhead valve (“OHV”) configuration for valve train  332  thereof. Similar to valve train  110  of engine  50 , valve train  332  of engine  300  operates on a conventional four-stroke cycle. 
   Referring to  FIGS. 22-24 , cylinder head includes a number of passages through which air, directed over the cylinder assemblies by flywheel  78 , may flow to cool cylinder heads  324  and rocker boxes  356 . A first air passage  358  extends between push rod sleeves  353  as shown in  FIGS. 22 and 23 , and also between valve guide reinforcement portions  360  of each cylinder head  324 , as shown in FIG.  24 . Second air passages  362   a  and  362   b  extend respectively between push rod sleeves  353  and intake and exhaust ports  328  and  330 . Third air passages  364   a  and  364   b  extend respectively between support struts  366  of each cylinder head  324  and intake and exhaust ports  328  and  330 . Airflow through air passages  358 ,  362   a,    362   b,    364   a,  and  364   b  cools cylinder heads  324 , particularly exhaust ports  330 , as well as rocker boxes  356 , during running of engine  300 . 
   Referring to  FIG. 25 , engine  400  is shown, which is a twin cylinder opposed engine including the identical cylinder members  74   a  and  74   b  of engine  50 . Cylinder members  74   a  and  74   b  are each attached to opposite walls of crankcase  402  in the same manner as discussed above with respect to engine  50 , and are disposed directly opposite one another to provide an opposed arrangement. The components of the cylinder members  74   a  and  74   b , as well as several other components of engine  400 , are identical to those described above with respect to engine  50 , and identical reference numerals are used to designate the various components which may be shared therebetween. In this manner, engine  400  includes the identical side valve or “L-head” valve train  110  as engine  50 . Crankshaft  58  of engine  400  is disposed vertically; however, engine  400  may alternatively be configured such that crankshaft  58  is disposed horizontally. Crankcase  402  includes first crank bearing  404 , and crankcase cover  404  is attached to the open upper end of crankcase  402  to enclose same, and includes second crank bearing  406 . Connecting rods  93  are attached to a common crank pin  99  of crankshaft  58 , and cylinder members  74   a  and  74   b  are therefore staggered with respect to one another along the length of crankshaft  58 . 
   Advantageously, the cylinder members  74   a  or  74   b  of engine  50  may also be used in single cylinder engines without modifications to the cylinder members. For example, as shown in  FIG. 26 , a cylinder member, such as  74   b , is shown in a vertical crankshaft, single cylinder engine  500 . Engine  500  includes crankcase  502  having a vertically disposed crankshaft  58  journalled in upper crank bearing  506  and lower crank bearing  508 . The components of the cylinder member  74   b , as well as several other components of engine  500 , are identical to those described above with respect to engine  50 , and identical reference numerals are used to designate the various components which may be shared therebetween. In this manner, engine  500  includes the identical side valve or “L-head” valve train  110  as engine  50 . Piston  91  reciprocates within cylinder bore  90 , and connecting rod  93  is connected at one end thereof to piston  91  by wrist pin  510 , and at an opposite end thereof to crankpin  99  of crankshaft  58  by split cap  97 . Engine  500  additionally includes flywheel  78  and a recoil starter mechanism  512 , each mounted to an end of crankshaft  58  which extends externally of crankcase  502 . Shroud/blower housing  514  covers the upper portion of crankcase  502  and cylinder member  74   b  for directing cooling air from flywheel  78  over crankcase  502  and cylinder member  74   b . Fuel tank  516  with fuel tank cap  518  are attached to shroud  514  in a suitable manner. 
   In  FIG. 27 , cylinder member  74   a  is shown in a horizontal crankshaft, single cylinder engine  600 . The components of the cylinder member  74   a , and several other components of engine  600 , are identical to those described above with respect to engine  50 , and identical reference numerals are used to designate the various components which may be shared therebetween. In this manner, engine  600  includes the identical side valve or “L-head” valve train  110  as engine  50 . Engine  600  includes crankcase  602 , which is configured for attachment of cylinder member  74   a  vertically there above such that engine  600  has a vertical overall profile or orientation. Crankcase  602  includes a horizontally disposed crankshaft  58 . Drive gear  150  is mounted on crankshaft  58  for engaging cam gear  156 , and cam gear  156  also drives auxiliary gear  606  for powering an auxiliary device such as a governor, for example. Additionally, carburetor  116  is mounted to intake port  98  of cylinder member  74   a , and muffler  608  is mounted to exhaust port  100  of cylinder member  72   a.    
   In  FIG. 28 , cylinder member  74   a  is shown in a horizontal crankshaft, single cylinder engine  700 . The components of the cylinder member  74   a  and other components of engine  700  are identical to those described above with respect to engine  50 , and identical reference numerals are used to designate the various components which may be shared therebetween. In this manner, engine  700  includes the identical side valve or “L-head” valve train  110  as engine  50 . Engine  700  includes crankcase  702 , which is configured for attachment of cylinder member  74   a  at an angle with respect to crankcase  702 , such that engine  700  has an overall slant profile or orientation. Carburetor  116  is mounted to intake port  98  of cylinder member  74   a , and muffler  704  is mounted to exhaust port  100  of cylinder member  72   a.    
   Although engines  400 ,  500 ,  600 , and  700  are shown above having one or more of cylinder members  74   a  and  74   b  of engine  50  to provide a side valve or “L-head” valve train  110 , engines  400 ,  500 ,  600 , and  700  could alternatively include one or more of cylinder members  306   a  and  306   b  of engine  300 , together with cylinder heads  324 , to provide an (“OHV”) valve train  332 . Additionally, each said cylinder member herein may be configured as an overhead cam (“OHC”) valve train, in which a camshaft located in the cylinder head of the cylinder member includes cam lobes for driving intake and exhaust valves, the camshaft driven from the crankshaft in a suitable manner, such as through a gear set or by a belt or a chain, for example. As used herein, the phrase “type” of valve train refers to any one or more of a side valve or “L-head” valve train, an overhead valve (“OHV”) valve train, or an overhead cam (“OHC”) valve train. 
   Further, in each of the engines disclosed herein, the particular cylinder member(s)  74   a ,  74   b  and  306   a,    306   b  which are used may be selected to determine a desired location of the intake and exhaust ports of the cylinder members, and in turn, the location of the carburetor and muffler for each engine. For example, in  FIG. 27 , cylinder member  72   a  is used in engine  600 , which places intake port  98  and carburetor  116  on the right side of engine  600 , and exhaust port  100  and muffler  608  on the left side of engine  600 . However, cylinder member  72   b , which has opposite intake and exhaust ports may also be used in engine  600  in place of cylinder member  72   a  and, with reference to  FIG. 27 , would therefore place intake port  98  and carburetor  116  on the left side of engine  600  and exhaust port  100  and muffler  608  on the right side of engine  600 . 
   Therefore, the cylinder members  74   a ,  74   b  and  306   a,    306   b  of the above-described engines  50  and  300  are common, modular components which may be used both in single cylinder and in twin cylinder engines, thereby reducing the number of engine components used for manufacturing single and twin cylinder engines and reducing the costs associated with manufacturing the foregoing engines. 
     FIGS. 29 and 30  illustrate the modularity of the engine components of the present line of engines, and in particular, how the various different crankcases and different cylinder members disclosed herein are compatible with one another to selectively construct a number of different types of small internal combustion engines. In  FIG. 29 , a variety of crankcases are shown, including crankcase  52  ( FIGS. 7 and 13 ) for two cylinder V-twin horizontal crankshaft engine  50 , crankcase  302  ( FIGS. 19 and 20 ) for two cylinder V-twin vertical crankshaft engine  300 , crankcase  402  ( FIG. 25 ) for two cylinder (opposed) engine  400 , crankcase  502  ( FIG. 26 ) for single cylinder vertical crankshaft engine  500 , crankcase  602  ( FIG. 27 ) for single cylinder horizontal crankshaft (upright) engine  600 , and crankcase  702  ( FIG. 28 ) for single cylinder horizontal crankshaft (slant) engine  700 . 
   Each of the foregoing crankcases includes common mounting structure, shown in  FIGS. 29 and 30  and discussed above with reference to crankcase  52  of engine  50 , including one or more cylinder mounts each having mounting surface  72  and opening  76 . Each cylinder mount is adapted for connection thereto of cylinder member  74  having a side valve or “L-head” valve train  110  ( FIGS. 11 ,  12 , and  30 ), or cylinder member  306  having an overhead valve (“OHV”) valve train  332  (FIGS.  24  and  30 ). In this manner, each engine may be selectively configured with a side valve or “L-head” valve train or with an overhead valve (“OHV”) valve train. As schematically shown in  FIG. 29 , in view of the six different types of crankcases  52 ,  302 ,  402 ,  502 ,  602 , and  702 , and the two different types of cylinder members  74  and  306 , the following 14 different types of engines “E”, also set forth in Table I below, may be selectively constructed: 
   
     
       
         
             
             
             
           
             
               TABLE I 
             
             
                 
             
             
                 
                 
               Cylinder 
             
             
               Type of engine “E” (FIG. 29) 
               Crankcase 
               member(s) 
             
             
                 
             
           
          
             
               V-twin, horizontal shaft, 
               Crankcase 52. 
               Two cylinder 
             
             
               L-head valve train 
                 
               members 74. 
             
             
               V-twin, horizontal shaft, 
               Crankcase 52. 
               Two cylinder 
             
             
               OHV valve train. 
                 
               members 306. 
             
             
               V-twin, vertical shaft, 
               Crankcase 302. 
               Two cylinder 
             
             
               L-head valve train 
                 
               members 74. 
             
             
               V-twin, vertical shaft, OHV valve train. 
               Crankcase 302. 
               Two cylinder 
             
             
                 
                 
               members 306. 
             
             
               Two cylinder opposed, horizontal shaft, 
               Crankcase 402. 
               Two cylinder 
             
             
               L-head valve train. 
                 
               members 74. 
             
             
               Two cylinder opposed, horizontal shaft, 
               Crankcase 402. 
               Two cylinder 
             
             
               OHV valve train. 
                 
               members 306. 
             
             
               Two cylinder opposed, vertical shaft, 
               Crankcase 402. 
               Two cylinder 
             
             
               L-head valve train. 
                 
               members 74. 
             
             
               Two cylinder opposed, vertical shaft, 
               Crankcase 402. 
               Two cylinder 
             
             
               OHV valve train. 
                 
               members 306. 
             
             
               Single cylinder, vertical shaft, 
               Crankcase 502. 
               One cylinder 
             
             
               L-head valve train 
                 
               members 74. 
             
             
               Single cylinder, vertical shaft, OHV 
               Crankcase 502. 
               One cylinder 
             
             
               valve train 
                 
               members 306. 
             
             
               Single cylinder, horizontal shaft, 
               Crankcase 602. 
               One cylinder 
             
             
               upright configuration, L-head valve 
             
             
               train. 
                 
               members 74. 
             
             
               Single cylinder, horizontal shaft, 
               Crankcase 602. 
               One cylinder 
             
             
               upright configuration, OHV valve train. 
                 
               members 306. 
             
             
               Single cylinder, horizontal shaft, slant 
               Crankcase 702. 
               One cylinder 
             
             
               configuration, L-head valve train. 
                 
               members 74. 
             
             
               Single cylinder, horizontal shaft, slant 
               Crankcase 702. 
               One cylinder 
             
             
               configuration, OHV valve train. 
                 
               members 306. 
             
             
                 
             
          
         
       
     
   
   Referring to  FIG. 30 , each cylinder member  74  and  306  includes a cam gear  156  rotatably mounted thereto in the manner described above. In each of cylinder members  74  and  306 , a portion of cam gear  156  extends externally of its respective cylinder member  74  and  306 . When cylinder member  74  or cylinder member  306  is attached to the mounting surface  72  of one of the crankcases, such as crankcase  50  as shown in  FIG. 30 , the foregoing portion of cam gear  156 , which extends externally of its respective cylinder member, extends through opening  76  in crankcase  50  and internally within crankcase  50  for driving engagement with drive gear  150  mounted to crankshaft  58 . 
   The cylinder members are attached to their respective crankcase using suitable fasteners, as described above and shown in  FIG. 13  with respect to engine  50 . In this manner, each crankcase  50 ,  302 ,  402 ,  502 ,  602 , and  702  may be fitted with one or more cylinder members  74  to provide a side valve or “L-head” valve train  10 , or alternatively, may be fitted with one or more cylinder members  306  to provide an overhead valve (“OHV”) valve train  332 . 
   While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.