Abstract:
To simplify the assembling process to mount a valve operating mechanism on a cylinder head, one intake valve and one exhaust valve are mounted on the cylinder head symmetrically with respect to the axis of a cylinder shaft. A rocker arm supporting base which supports rocker arms is fixed to the top of the cylinder head. Rocker arm shafts are supported by the base. The central portions of the rocker arms engage with the rocker arm shafts in such a way that the arms are free to swing. Push rods and the intake and exhaust valves are engaged with the ends of the arms. The valve operating mechanism is enclosed in a head cover which is fixed to the top surface of the cylinder head. This engine is distinguished by having the mounting surface for the rocker arm supporting base, on which the rocker shafts are mounted, and the surface on which the head cover sits be virtually coplanar. This makes it possible to machine the two surfaces at the same time. In order to supply a sufficient quantity of lubricating oil to the entire valve operating mechanism, a particularly designed lubrication device is provided.

Description:
FIELD OF THE INVENTION 
     This invention concerns a structure of an overhead-valve internal combustion engine and the manufacturing method for it. More specifically, it concerns the configuration of the valve operating mechanism which operates the valves in an overhead-valve type internal combustion engine with an intake valve and an exhaust valve, and the lubrication device in the valve operating mechanism of the same kind of engine. 
     BACKGROUND OF THE INVENTION 
     It is relatively simple to assemble the valve-operating mechanism in an engine with the aforesaid bathtub-type combustion chamber. However, the combustion efficiency of this chamber is inferior to that of the aforesaid pent roof-type. In recent years, this has led to greater use of pent roof chambers. 
     FIGS. 18 and 19 show an example of an air-cooled single-cylinder overhead-valve four-cycle internal combustion engine with the aforesaid pent roof combustion chamber which belongs to the prior art. FIG. 18 is a cross section of the engine which includes the cylinder and the push rods. FIG. 19 is a cross section taken along line Z—Z in FIG.  18 . 
     In FIGS. 18 and 19,  1  is the combustion chamber;  2  is the air-cooled cylinder;  5  is the crankshaft;  6  is the connecting rod;  7  is the piston;  8  is the cylinder head;  14   a  is the intake valve; and  14   b  is the exhaust valve (Hereafter, the aforesaid intake valve  14   a  and exhaust valve  14   b  will be referred to in common as induction/exhaust valves  14 .) 
       17  is the camshaft, which is engaged with the aforesaid crankshaft  5  through a gear train;  17   a  is the cam on the said camshaft  17 ;  16  is the tappet;  15  is the push rod;  13  is the rocker arm shaft, which is fixed to and supported on rocker arm supporting base  22 , which is itself fixed to the top of the aforesaid cylinder head  8 .  11  is the rocker arm, which engages with the said rocker arm shaft  13  in such a way that it is free to swing.  18  is the valve spring.  19  is the valve spring bearing.  9  is the head cover, which is mounted on top surface  8   b  on top of cylinder head  8  and which covers the mechanism which operates the valves. When this engine operates, induction/exhaust valves  14  open and close according to a timing determined by cam  17   a , whose rotating speed is reduced to half that of crankshaft  5  by a timing gear (not pictured). 
     In FIG. 18, the rotation of camshaft  17   a  forces push rods  15  upward, and rocker arms  11  swing around shaft  13 . Intake valve  14   a  or exhaust valve  14   b  is pushed upward against the elastic force of valve spring  18 , and the valve opens. 
     In an OHV engine like this, to insure that the action of cam  17   a  is transmitted reliably to induction/exhaust valve  14  through push rods  15 , the aforesaid valve spring  18  must have a relatively large spring constant, meaning that a strong spring must be used; and rocker arm shaft  13  must have a relatively large diameter. 
     To insure that the contacting surfaces of the valve operating mechanism do not experience excessive force when the engine is running and the cylinder head gets hot, an adjustment screw (not pictured) is provided to adjust the clearance between the contacting portions of rocker arms  11  and push rods  15 . 
     In the aforesaid cylinder head  8 , the aforesaid head cover  9  is hermetically sealed to top surface  8   b , the upper surface of peripheral wall  8   c , which surrounds the head. The aforesaid rocker arm supporting base  22  for the rocker arms is bolted to an area in the center of upper surface  8   a  which is lower than the said top surface  8   b  by a fixed amount. 
     In the four-cycle overhead valve internal combustion engine from the prior art which is pictured in FIGS. 18 and 19, there are two surfaces at the top of cylinder head  8 ,  8   b  and  8   a .  8   b  is the top surface onto which head cover  9  is fixed;  8   a  is the mounting surface on which rocker arm supporting base  22 , which supports the rocker arms, is fixed. These two surfaces must be finished by a machining process so that they are relatively smooth. 
     However, in the prior art cylinder head  8 , top surface  8   b , on which cover  9  is mounted, and mounting surface  8   a , on which rocker arm supporting base  22  is mounted, are at different heights. This means that they must be machined in a two-stage process or that the machinist must change tools in mid-process. This increases the number of processes required and incurs an extra cost for set-up. 
     Designs for overhead valve engines with a hemispherical combustion chamber and the intake and exhaust valves arranged so that they radiate from the center have been proposed in Japanese Patent Publications (Kokai) Hei5-133205. In this prior art, one intake valve, one exhaust valve, and one spark plug are arranged so that the angles of these center lines (L 1 ), (L 2 ), (L 3 ) against the center line of cylinder are same as each other, and they are located at a same distance from the center of the cylinder in order to manufacture the cylinder easily. 
     Another prior art is proposed in Japanese Patent Publications (Kokai) Hei5-133205. In both of these, however, the structure which supports the valve operating mechanism in the cylinder head is three-dimensional. It is difficult to achieve the high level of precision required by the processing, and the structural components of the valve operating mechanism experience torsion force when the valves are driven, which shortens their service life. 
     For a structure of a lubrication device for an OHV engine, there is a breather passage between the crankcase and the valve operating mechanism chamber which contains the valve operating mechanism. Oil which is taken up by a dipper, splashed about and suspended in the crankcase is conveyed via this breather passage into the aforesaid valve operating mechanism chamber with the movement of air caused by the downward stroke of the piston. In this way the said valve operating mechanism chamber is lubricated. 
     An example of an existing lubrication device for the valve operating mechanism in a small multipurpose OHV engine can be found in Japanese Utility Model Publication (Kokoku) 63-15530. The details of this device are shown in FIGS. 20 through 22. 
     These drawings show an OHV engine whose cylinder is canted upward from the horizontal. Breather passage  131 , which connects crankcase  101  and valve operating mechanism chamber  102 , is formed within the walls of cylinder barrel  116  and cylinder head  118 . 
     The end portion  131   a  of the said breather passage  131  in valve operating mechanism chamber  102  faces from above intake valve  151  toward the point where valve stem  152   a  of exhaust valve  152  and rocker arm  162  come in contact. Branching passage  131   b  faces to the point where valve stem  151   a  of intake valve  151  and rocker arm  161  come in contact. 
     Because this OHV engine is configured in this prior art, the air which is moved by the downward stroke of piston  107  forces the oil picked up by dipper  115  and suspended in crankcase  101  into the aforesaid breather passage  131 . The greater part of this suspended oil goes in a straight line through portion  131   a  and is splashed upon the operating mechanism for exhaust valve  152  in the vicinity of the point where valve stem  152   a  and rocker arm  162  come in contact. This is how most of the suspended oil is supplied. 
     The remainder of the suspended oil goes through branching passage  131   b  and is splashed upon the operating mechanism for intake valve  151  in the vicinity of the point where valve stem  151   a  and rocker arm  161  come in contact. 
     When the air forced into the aforesaid valve operating mechanism chamber  102  goes through breather valve  108 , the lubricating oil is separated out. The air enters breather chamber  109 , travels through breather tube  132  and is returned to carburetor  111 . The oil flows down the interior surface of valve operating mechanism chamber  102 . It goes through the space around push rod  122  and tappet  121  and is recovered in crankcase  101 . 
     In this prior art OHV engine disclosed in the Japanese Utility Model Publication (Kokoku) 63-15530, as may be seen in FIG. 21, intake and exhaust valves  151  and  152  are parallel to each other, and the distance traveled by the aforesaid two valves, which protrude into valve operating mechanism chamber  102 , is relatively short. Breather passage  131 , which goes through the aforesaid crankcase  101  and valve operating mechanism chamber  102 , is formed in the thick portion within the walls of cylinder barrel  117  and cylinder head  118 . 
     In recent years, more and more pent roof combustion chambers have been used in OHV engines to increase combustion efficiency. In an engine with a pent roof combustion chamber, the intake and exhaust valves are canted at a given angle with respect to the axis of the cylinder barrel, with the open side of the angle toward the exterior. As a result, a large space must be provided at the front end of the intake and exhaust valves, where they protrude into the valve operating mechanism chamber for the operating mechanism. At the same time, every possible structural component has been made thinner in the interest of reducing the weight of the engine, and every possible space has been made smaller. With the prior art design, it has proved impossible to simplify the breather passage without increasing the parts count. With the current breather passage, the exhaust valve does not receive sufficient lubrication, which shortens the service life of the engine. 
     SUMMARY OF THE INVENTION 
     In view of the problems inherent in the prior art, our first objective in designing this invention is to provide an overhead-valve internal combustion engine with one intake and one exhaust valve which would have the following features. The surface in the cylinder head on which the rocker arm supporting base which supports the rocker arms is mounted and the surface on which the head cover sits can be formed on the same level. This configuration will be able to simplify the assembling process to mount the valve operating mechanism on the cylinder head. The number of production processes and assembly processes would be reduced, and the engine will be able to be made at a lower cost. 
     Our second objective in designing this invention is to provide a lubrication device for an overhead valve engine with a pent roof combustion chamber such that the breather passage in the valve operating mechanism chamber for the valve operating mechanism would be simplified without increasing the parts count so that a sufficient quantity of lubricating oil can be supplied to the entire valve operating mechanism. 
     In order to address the above objectives, we propose the following preferred embodiments according to this invention. 
     The first preferred embodiment of the invention is an overhead-valve internal combustion engine with a hemispherical or pent roof cylinder head. Such a head has a combustion chamber being formed with a curved top portion projecting upward. One intake valve and one exhaust valve are mounted symmetrically with respect to the axis of the cylinder shaft. The rocker arm supporting base which supports the rocker arms is fixed to the top of the aforesaid cylinder head. The rocker arm shaft is supported by the said base. The central portion of the rocker arms engages with the said rocker arm shaft in such a way that the arms are free to swing. The push rods and the aforesaid intake and exhaust valves are connected to the ends of the arms. The valve operating mechanism comprising the aforesaid intake and exhaust valves, the supporting base for the rocker arm shaft, and the rocker arms are enclosed in the head cover which is fixed to the top surface of the aforesaid cylinder head. This engine is distinguished by the fact that on the top surface of the aforesaid cylinder head, the surface for the rocker arm supporting base on which the aforesaid rocker shaft are mounted and that on which the head cover sits are coplanar. More specifically, either these two surfaces are coplanar or the surface of the rocker arm supporting base which is formed in the center of the cylinder head is slightly higher than the aforesaid surface on which the cover sits. 
     In another example of the first preferred embodiment of the invention, the aforesaid cylinder head in the overhead-valve internal combustion engine according to the first preferred embodiment ideally has a surface on which the head cover can sit which is formed on the top of the peripheral wall. The mounting surface of the aforesaid rocker arm supporting base is formed on two bosses which extend from the aforesaid peripheral wall toward the interior of the head. 
     According to these examples of the first preferred embodiment, the mounting surface of the cylinder head on which is mounted the rocker arm, the ancillary components such as the adjustment screws which are mounted on the said rocker arms, and the rocker arm supporting base to support the rocker arm shaft, is level with the top surface on the upper surface of the peripheral wall or the mounting surface positioned in the center of the cylinder head is same as, or slightly higher than, the top surface. This makes it possible to machine the two surfaces at the same time. 
     Thus there is no need for two-stage processing or changing tools during processing, as was the case with prior art designs. This design significantly reduces the number of processes required, and the simultaneous machining described above results in a highly planar surface, which translates into greater precision. 
     Yet in another example of the first preferred embodiment, the rocker arm supporting base according to the first embodiment is mounted in the center of the top of the aforesaid cylinder head. The aforesaid intake and exhaust valves are on either side of the said rocker arm supporting base. The aforesaid rocker arm shafts are supported at two places to the aforesaid rocker arm supporting base, and they are symmetrical with respect to the center of the cylinder. One shaft is provided for the intake valve and one for the exhaust valve. The shafts are arranged so that they are parallel to each other within the base which is parallel to the mounting surface of the cylinder head. The aforesaid rocker arms are inserted into the shafts for the aforesaid intake and exhaust valves. The supporting portion of each rocker arm which is inserted into one of the aforesaid shafts is sandwiched between two arm units, the first arm unit which is engaged with one of the push rods and the second arm unit which pushes the intake valve. 
     With this configuration, the shafts for the two rocker arms are fixed to the rocker arm supporting base at both ends. This minimizes the torsion force which acts on the shafts when the rocker arms operate and allows us to achieve rocker arms and a shaft supporting mechanism with a high degree of strength. 
     In the second preferred embodiment of this invention, the aforesaid rocker arm supporting base according to the first embodiment is mounted to the center of the top of the aforesaid cylinder head. The aforesaid intake and exhaust valves are on both sides of the said rocker arm supporting base. The one end of the aforesaid rocker arm shafts in the center of the engine is supported by the aforesaid rocker arm supporting base. The shaft for the intake valve extends from the rocker arm supporting base at a right angle to the axis of the intake valve, the shaft for the exhaust valve extends from the rocker arm supporting base at a right angle to the axis of the exhaust valve. Each of the aforesaid rocker arms has a central supporting portion which is inserted into one of the shafts. The supporting portion of each rocker arm which is inserted into one of the aforesaid shafts is sandwiched between two arm units, the first arm unit of which is engaged with one of the push rods and the second arm unit of which pushes the intake valve. 
     With this configuration, the rocker arm shafts are fixed to both sides of the rocker arm supporting base. This allows the rocker arm supporting base to be made smaller, and a smaller mounting surface on the cylinder head will suffice. As a result, fewer processes are required to produce the said mounting surface. 
     Furthermore, the rocker arms can be made longer so as to prevent the expenditure of unnecessary force in the valve operating mechanism. 
     In the third preferred embodiment of this invention, the axes of the aforesaid two rocker arm shafts according to the second preferred embodiment, when viewed from above, are at a fixed angle with respect to a line linking the axes of the aforesaid intake and exhaust valves, and they separate from each other more as they move away from the center. 
     With this configuration, the point at which the rocker arm is engaged with the push rod and the point at which it is in contact with the intake or exhaust valve are arranged in a straight line on either side of the axis of the rocker arm shaft. 
     In another example of the first preferred embodiment of this invention, an engine according to the first embodiment has a hemispherical or pent roof cylinder head with a combustion chamber being formed with a curved top portion projecting upward. One intake valve and one exhaust valve are mounted symmetrically with respect to the axis of the cylinder shaft. The rocker arm supporting base is fixed to the top of the aforesaid cylinder head. The rocker arm shafts are supported by the said rocker arm supporting base. The central portion of the rocker arms engages with the said rocker arm shafts in such a way that the arms are free to swing. The push rods and the aforesaid intake and exhaust valves are engaged with the ends of the arms. The aforesaid shafts and rocker arms are firstly mounted to the aforesaid rocker arm supporting base, then secondly the rocker arm supporting base can be mounted on the surface prepared for it in the aforesaid cylinder head. 
     According to this configuration, rocker arm shafts and rocker arms are assembled to the rocker arm supporting base as a unit, then the base is mounted on the mounting surface for the rocker arm supporting base. This makes the assembling process easier and reduces the assembling count. 
     The ideal manufacturing method for manufacturing an internal combustion engine according to this invention is proposed as the following two examples. A cylinder head is prepared which has a combustion chamber whose roof curves upward. The top surface of this head is formed in such a way that the mounting surface of the aforesaid rocker arm supporting base and the top surface on which the head cover sits are coplanar. An assembly component is prepared which comprises the rocker arm supporting base on which the shafts and the rocker arms have been mounted. 
     The assembly component which includes the rocker arms is fixed to the top of the aforesaid cylinder head. The intake and exhaust valves are mounted so that they are symmetrical with respect to the axis of the cylinder. The push rods and the aforesaid intake and exhaust valves are engaged, respectively, to the opposite ends of the aforesaid rocker arms. 
     According to the other example of the ideal manufacturing method, the manufacturing method of manufacturing an overhead-valve internal combustion engine is distinguished by the following. The intake and exhaust valves and push rods of the combustion chamber are mounted to the cylinder head. The rocker arms, rocker arm shafts, rocker arm supporting base, adjustment screws to adjust the gap between the valves and lock nuts are assembled as a unit, which is then mounted to the surface prepared for it, a surface which is virtually level with that on which the head cover sits. The head cover is then fixed to the cylinder head. 
     With these manufacturing methods mentioned above, the rocker arm shafts, the rocker arms and their ancillary components are all mounted on the rocker arm supporting base to form a unit, which is then mounted to the cylinder head. This procedure simplifies the assembly and adjustment of the valve operating mechanism and reduces the number of procedures required. 
     The fourth preferred embodiment is for the lubrication device for OHV engine. 
     According to the fourth preferred embodiment of this invention, a lubrication device for overhead-valve engine having a first breather passage connecting a valve operation mechanism chamber over a cylinder head provided with an intake valve and an exhaust valve, and a crankcase, and passing through said cylinder head and a cylinder, comprises an opening of a first breather passage, a groove, and a second breather passage. 
     The opening of the first breather passage is provided in a vicinity of a spring retainer for the intake valve, which faces the valve operating mechanism chamber. 
     The groove is formed by cutting on the cylinder head facing the valve operating chamber and connecting an end of the groove to the opening. 
     The second breather passage is formed by a tunnel-like passage provided by a guide wall standing in the valve operating mechanism chamber and a peripheral wall of said cylinder head and connecting another end of said groove to the exhaust valve. 
     According to another example of the fourth preferred embodiment, the second breather passage mentioned above further comprises a protruding portion of a gasket provided between a top surface of the cylinder head and a head cover, which covers the tunnel-like passage. 
     According to yet another example of the fourth preferred embodiment, the second breather passage connects spaces surrounded with ring-shaped ribs which protrude from spring retainers for an intake valve spring and an exhaust valve spring by the groove formed by cutting on a portion of the ring-shaped rib and the tunnel-like passage. 
     With this fourth preferred embodiment of the invention, the lubricating oil splashed around in the crankcase goes through the first breather passage and flows out through the opening of the valve operating mechanism chamber in the vicinity of the spring retainer for the intake valve. From the vicinity of the said intake valve, the oil goes through the second breather passage, which comprises a groove formed on the valve operating mechanism chamber surface of the cylinder head and a tunnel surrounded by a guide wall and the peripheral wall of the cylinder head. This passage conducts the oil to the vicinity of the exhaust valve. 
     With this fourth preferred embodiment of the invention, a sufficient quantity of lubricating oil can be supplied not only to the area around the intake valve, but also, via the second breather passage, to the area around the exhaust valve, where extreme temperatures are experienced. The entire valve operating mechanism can be lubricated uniformly. 
     Because the aforesaid second breather passage can be created using the valve operating mechanism chamber surface of the cylinder head and the protruding portion of the gasket, no special parts need to be purchased or made, and the parts count can be reduced. 
     The effects of this invention related to the structure of the cylinder head according the first through third preferred embodiments of this invention are as follows. In these configurations mentioned above, the mounting surface of the cylinder head on which is mounted the rocker arm, and the rocker arm supporting base to support the rocker arm shaft, is level with the top surface on the upper surface of the peripheral wall, or the mounting surface positioned in the center of the cylinder head is slightly higher than the top surface. This makes it possible to machine the two surfaces at the same time. 
     Thus there is no need for two-stage processing or changing tools during processing, as was the case with prior art designs. This design significantly reduces the number of processes required; and the simultaneous machining described above results in a highly planar surface, which translates into greater precision. 
     With the configuration according to the example of the first preferred embodiment mentioned above, the shafts for the two rocker arms are fixed to the rocker arm supporting base at both ends, in other words, the shafts are supported at both ends. This minimizes the torsion force which acts on the shafts when the rocker arms operate and allows us to achieve rocker arms and a shaft supporting mechanism with a high degree of strength. 
     With the configuration according to the second preferred embodiment mentioned above, the rocker arm shafts are fixed at one end. This allows the rocker arm supporting base to be made smaller, and a smaller mounting surface on the cylinder head will suffice. As a result, fewer processes are required to produce the said mounting surface. 
     Furthermore, the rocker arms can be made longer so as to prevent the expenditure of unnecessary force in the valve operating mechanism, and the durability of the valve operating mechanism can be enhanced. 
     With the configuration according to the third preferred embodiment, the point at which the rocker arm is engaged with the push rod and the point at which it is in contact with the intake or exhaust valve are arranged in a straight line on either side of the axis of the rocker arm shaft. 
     With the manufacturing method mentioned above, the rocker arm shafts, the rocker arms and their ancillary components are all mounted on the rocker arm supporting base to form a unit, which is then mounted to the cylinder head. This procedure simplifies the assembly and adjustment of the valve operating mechanism and reduces the number of procedures required. 
     The mounting surface of the cylinder head on which is mounted the rocker arm, and the rocker arm supporting base to support the rocker arm shaft, is level with the top surface on the upper surface of the peripheral wall, or the mounting surface positioned in the center of the cylinder head is slightly higher than the top surface. This makes it possible to machine the two surfaces at the same time. 
     Thus there is no need for two-stage processing or changing tools during processing, as was the case with prior art designs. This design significantly reduces the number of processes required; and the simultaneous machining described above results in a highly planar surface, which translates into greater precision. 
     The effects of the invention related to the lubrication device according the fourth preferred embodiment are as follows. In these configurations of this invention, the lubricating oil splashed around in the crankcase goes through the opening in the vicinity of the spring retainer for intake valve. From the vicinity of the said intake valve, the suspended oil goes through the second breather passage formed by a groove and a tunnel which is surrounded by a straight guide wall and the peripheral wall of the cylinder head. This passage conducts the suspended oil to the vicinity of the exhaust valve. In this fashion, a sufficient quantity of lubricating oil can be supplied not only to the area around the intake valve, but also to the area around the exhaust valve, where extreme temperatures are experienced. The entire valve operating mechanism can be lubricated uniformly. 
     Because the aforesaid breather passage can be created using the valve operating mechanism chamber surface of the cylinder head and the entrance portion of the oil guide washer plate, no special parts need to be used, and it is easy to assemble the valve operating mechanism chamber. In other words, the parts count can be reduced, and the entire valve operating mechanism can be lubricated perfectly with a low cost. 
    
    
     BRIEF EXPLANATION OF THE DRAWINGS 
     FIG. 1 is a cross section of an air-cooled overhead-valve single cylinder four-cycle internal combustion engine which is the first configuration of this invention. This drawing shows primarily the cylinder and the push rod. 
     FIG. 2 is a plan view of the engine in FIG. 1 with the head cover removed. 
     FIG. 3 is a cross section taken along line A—A in FIG.  2 . 
     FIG. 4 corresponds to FIG. 2, which shows the second configuration of the second preferred embodiment of this invention. 
     FIG. 5 is a cross section taken along line B—B in FIG.  4 . 
     FIG. 6 is the view of the cylinder head in FIG. 5 as seen from arrow C in that figure (when seen through the valve operating mechanism). 
     FIG. 7 corresponds to FIG. 2 but shows the third preferred embodiment of this invention. 
     FIG. 8 is a cross section taken along line D—D in FIG.  7 . 
     FIG. 9 is a view of the same cylinder head as seen from arrow E in FIG. 8 (when seen through the valve operating mechanism). 
     FIG. 10 corresponds to FIG.  1  and shows an aircooled overhead-valve four-cycle internal combustion engine which is an example of the fourth preferred embodiment of this invention. This shows the cross section showing the center of the cylinder and the push rod. 
     FIG. 11 is a plan view of the valve operating mechanism from the engine in FIG. 1 with the head cover removed according to the fourth preferred embodiment of this invention. 
     FIG. 12 is a cross section taken along line F—F in FIG.  11 . 
     FIG. 13 shows a plan view of the valve operating mechanism in a multipurpose OHV engine which is the fourth preferred embodiment of this invention. The head cover has been removed. 
     FIG. 14 is a plan view of the cylinder head in the aforesaid fourth preferred embodiment. 
     FIG. 15 is a cross section taken along line G—G in FIG.  14 . 
     FIG. 16 is a cross section taken along line H—H in FIG.  14 . 
     FIG. 17 shows the oil guide washer plate in the aforesaid fourth preferred embodiment. (a) is a frontal view and (b) is a plan view. 
     FIG. 18 is a lateral cross section, cut along the center line of the cylinder and push rod, of a multipurpose OHV engine which is an example of the prior art. 
     FIG. 19 is a cross section taken along line Z—Z in FIG.  18 . 
     FIG. 20 is a vertical cross section of another example of the prior art. 
     FIG. 21 is a vertical cross section of the prior art shown in FIG.  20 . 
     FIG. 22 is a plan view of the valve operating mechanism of the prior art shown in FIG.  20 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In this section we shall give a detailed explanation of several preferred embodiments of this invention with reference to the example configurations pictured in the drawings. To the extent that the dimensions, materials, shape and relative position of the components described in this configuration are not definitely fixed, the scope of the invention is not limited to those specified, which are meant to serve merely as illustrative examples. 
     FIG. 1 is a cross section of an air-cooled overhead-valve single cylinder four-cycle internal combustion engine which is the first preferred embodiment of this invention. This drawing shows primarily the cylinder and the push rod. FIG. 2 is a plan view of the engine in FIG. 1 with the head cover removed. FIG. 3 is a cross section taken along line A—A in FIG.  2 . 
     In FIGS. 1 through 3,  1  is the combustion chamber;  2  is the air-cooled cylinder;  5  is the crankshaft;  6  is the connecting rod;  7  is the piston;  8  is the cylinder head;  14   a  is the intake valve;  14   b  is the exhaust valve (hereafter, intake valve  14   a  and exhaust valve  14   b  are known collectively as induction/exhaust valves  14 );  51  is the spark plug; and  52  is the crankcase. 
       17  is the camshaft, which is connected to crankshaft  5  through a gear train:  17   a  is the cam formed on the said camshaft  17 ;  16  is the tappet;  15  is the push rod;  18  are the valve springs for the aforesaid induction/exhaust valves  14 ;  19  are the spring bearings which support the said valve springs  18 .  9  is the head cover, which encloses the valve operating mechanism (to be discussed shortly). This cover is mounted on top surface  101  of peripheral wall  8   c , which surrounds the aforesaid cylinder head  8 . 
     The aforesaid combustion chamber  1  is a pent roof-type chamber. This is why, as can be seen in FIG. 3, the aforesaid intake valve  14   a  and exhaust valve  14   b  are arranged so that their respective axes  103  and  104  angle away from the center line  102  of the cylinder. That is to say, the valves incline with respect to the center line at angle in the fashion of radiating lines. 
     This angle θ is such that 2θ=22° to 45°. Ideally, it should be in the neighborhood of 45°. 
       21  is the rocker arm for the intake valve.  21 ′ is the rocker arm for the exhaust valve. It is placed on the opposite side of center line  102  so that it is symmetrical with respect to the said rocker arm  21 .  23  are the rocker arm shafts, and  22  is the rocker arm supporting base. The aforesaid rocker arms  21  and  21 ′, rocker arm shafts  23 , rocker arm supporting base  22 , cam  17   a , tappet  16  and push rod  15  comprise the valve operating mechanism.  92  is the valve operating mechanism chamber to install the valve operating mechanism, and it is covered by the head cover  9 . 
     As can be seen in FIG.  2  and FIG. 3, the aforesaid rocker arm supporting base  22  is fixed by four bolts  25  to mounting surfaces  100 , the upper surfaces of the four bosses  8   d  which project from peripheral wall  8   c  of cylinder head  8  toward the center of the head. At the ends of the rocker arm supporting base are four retainers  22   a  and  22   b , which support the two rocker arms  23  for the aforesaid intake and exhaust valves at both their ends. These retainers also immobilize the two rocker arm shafts  23  so that they are parallel to each other. 
     Furthermore, as can be seen in FIG. 2, the aforesaid rocker arm shafts  23  are mounted onto the aforesaid rocker arm supporting base  22  so that their axes  23   a  are at a right angle with respect to line  105 , the line which links the centers of intake valve  14   a  and exhaust valve  14   b.    
     As is shown in FIG. 2, the central tubular portions of rocker arm  21 , which controls the aforesaid intake valve, and rocker arm  21 ′, which controls the exhaust valve, are supported by the aforesaid rocker arm shafts  23  in such a way that the rocker arms are free to swing and their movement in the axial direction can be controlled. Shafts  23  must have a diameter large enough to provide a sufficient bearing area.  21   b  and  21   ′b  are the first arm units on the ends of the arms which come in contact with push rods  15  in the axial direction of the aforesaid arms  23 .  21   c  and  21   ′c  are the second arm units on the ends of the arms which come in contact with intake valve  14   a  and exhaust valve  14   b.    
     Adjustment screws  24 , which serve to adjust the clearance of the valve operating mechanism, are screwed into the aforesaid arm units  21   b  and  21   ′b.  On the end of each adjustment screw  24  is a spherical bearing. The push rods  15  for the aforesaid intake and exhaust valves are linked to the rocker arms through these bearings. The aforesaid rocker arm units  21   c  and  21   ′c  contact with intake valve  14   a  and exhaust valve  14   b  through straps  21   a , which are made from a material that is highly resistant to being worn away. 
     Mounting surface  100  for rocker arm supporting base  22  on the upper surface of cylinder head  8  is coplanar (unifacial) with top surface  101 , on which head cover  9  is mounted. Ideally, the aforesaid mounting surface  100  and top surface  101  should be on the same plane. However, it would also be acceptable for them to be at slightly different levels. In this case, for the purpose of machining the surfaces, it would be better if the aforesaid top surface  101 , which is on the outside of the head, could be slightly lower than the mounting surface  100 , which is in the interior. 
     When this OHV engine is operating, induction/exhaust valves  14  open and close according to a timing determined by camshaft  17 , whose rotating speed is reduced to half that of crankshaft  5  by a timing gear (not pictured). That is to say, when camshaft  17  rotates, push rods  15  are thrust upward, and rocker arm  21 , which operates the intake valve, or rocker arm  21 ′, which operates the exhaust valve, rotates around shaft  23 . Intake valve  14   a  or exhaust valve  14   b  is pushed upward against the elastic force of its respective valve spring  18 , and the valve opens. 
     In an OHV engine like this, to insure that the action of cam  17   a  is transmitted reliably to induction/exhaust valve  14  through push rods  15 , the aforesaid valve springs  18  must have a relatively large spring constant, meaning that strong springs must be used; and, as was mentioned above, rocker arms  23  must have a relatively large diameter. 
     The upper surface of cylinder head  8 , on which is mounted rocker arm supporting base  22 , the base which supports the mechanism in cylinder head  8  that executes this operation, serves as mounting surface  100 . As was discussed earlier, this mounting surface is coplanar with top surface  101 , on which the head cover is mounted. This means that the two surfaces,  100  and  101 , can be finished together in the same machining process. There is no need, as was true in the prior art, to use a two-stage process or to change tools. In this first preferred embodiment, shafts  23  are fixed to rocker arm supporting base  22 , and rocker arm  21 , which operates the intake valve, and rocker arm  21 ′, which operates the exhaust valve, are inserted on the shafts with adjustment screw  24  already screwed in. Once this unit is assembled, it can be mounted to cylinder head  8 . This procedure simplifies both the assembly and the adjustment of the valve operating mechanism. 
     In this first preferred embodiment, rocker arm shafts  23  for the intake and exhaust valves are supported in two places by retainers  22   a  and  22   b  of rocker arm supporting base  22 . This minimizes the torsion force which acts on the shafts when the rocker arms operate and allows us to achieve rocker arms and a shaft support mechanism with a high degree of strength. 
     In the following second preferred embodiment, the structure of the rocker arm supporting base, and the rocker arm shaft are different from those of the first preferred embodiment. 
     In FIGS. 4 through 6,  27  is the rocker arm supporting base; it is fixed to mounting surface  100  by means of two bolts  25  at bosses  8   d , which project from peripheral wall  8   c  of cylinder head  8  toward the interior of the head at a right angle to line  105 , the line which links the centers of the aforesaid intake valve  14   a  and exhaust valve  14   b  to the center line  102  of the cylinder. 
     Just as in the first preferred embodiment, mounting surface  100  of the aforesaid rocker arm supporting base  27  is either coplanar with top surface  101  on which head cover  9  is mounted or slightly higher than that top surface. 
       28  are the rocker arm shafts. As can be seen in FIG. 4, their axes  28   a  when viewed from above are arranged so that they are virtually parallel to line  105 , the line linking the centers of the aforesaid intake and exhaust valves  14   a  and  14   b . The inner ends of the shafts are fixed to the aforesaid rocker arm supporting base  27 ; they are supported at only one end. 
     The aforesaid rocker arm shafts  28  are arranged so as to have an inclining angle with respect to the center line  102  of the cylinder, as can be seen in FIG.  5 . In this preferred embodiment, their axes  28   a  can form right angles with respect to the center lines  14   a   1  and  14   b   1  of intake and exhaust valves  14   a  and  14   b , which are arranged to the radiate direction with respect to the center line  102  of the cylinder head. 
       26  is the rocker arm for the intake valve;  26 ′ is the rocker arm for the exhaust valve. They are arranged symmetrically with respect to the center line  102  of the cylinder. The tubular portions in their centers are inserted into the aforesaid rocker arm shafts  28  in such a way that the arms are free to swing and their movement in the axial direction can be controlled. 
     The aforesaid axes  28   a  of rocker arm shafts  28  are surrounded by the aforesaid rocker arm  26  for the intake valve and  27 ′ for the exhaust valve. Their ends  26   b  and  26   ′b  come in contact with push rods  15 . Their other ends,  26   c  and  26   ′c,  come in contact with intake valve  14   a  and exhaust valve  14   b.    
     Adjustment screws  24  on ends  26   b  and  26   ′b  are used to adjust the clearance of the valve operating mechanism. The rocker arms are engaged with push rods  15  through the spherical bearings on the ends of the adjustment screws. 
     The aforesaid ends  26   c  and  26   ′c  are in contact with intake valve  14   a  and exhaust valve  14   b  through straps  26   a.    
     All other aspects of the configuration are identical to that of the first preferred embodiment shown in FIGS. 1 through 3. Components which are the same have been given the same numbers. 
     In this second preferred embodiment, just as in the aforesaid first preferred embodiment, mounting surface  100  for the rocker arm supporting base on the top of cylinder head  8  is either coplanar with top surface  101  on top of peripheral wall  8   c , to which head cover  9  is mounted, or slightly higher than that top surface. This design means that the two surfaces can be processed in a single stage, and the number of required processes is reduced. In addition, rocker arm supporting base  27  is smaller and the area of the said mounting surface  100  can be smaller than in the aforesaid first preferred embodiment. This further simplifies the processing of the said mounting surface  100  and reduces the number of processes. 
     In regard to configuration, the length of rocker arms  26  and  26 ′ can be increased, which provides some leeway in the design of the valve operating mechanism and prevents excessive force from being exerted in that mechanism. 
     FIGS. 7 through 9 show the third preferred embodiment of this invention. FIG. 7 is a plan view which corresponds to FIG.  2 . FIG. 8 is a cross section taken along line D—D in FIG.  7 . FIG. 9 is a view of the same cylinder head as seen from arrow E in FIG.  8 . 
     This preferred embodiment is a modification of the previous second one; the arrangement of the rocker arm supporting base and shafts differs from that in the second preferred embodiment. 
     In FIGS. 7 through 9,  32  is the rocker arm supporting base; it is fixed to mounting surface  100  by means of two bolts  25  on bosses  8   d , which project from peripheral wall  8   c  of cylinder head  8  toward the interior of the head at a right angle to line  105 , the line which links the centers of the aforesaid intake valve  14   a  and exhaust valve  14   b  to the center line  102  of the cylinder. As in the first two preferred embodiments, mounting surface  100  of the aforesaid rocker arm supporting base  32  is either coplanar with top surface  101  on which head cover  9  is mounted or slightly higher than that top surface. 
       33  are the rocker arm shafts. As can be seen in FIG. 7, their axes  33   a , when viewed from above, are arranged so that they incline from the center to the exterior to form angles α 1  and α 2  with respect to line  105 , the line linking the centers of the aforesaid intake and exhaust valves  14   a  and  14   b . The inner ends of the shafts are fixed to the aforesaid rocker arm supporting base  32 ; the shafts are supported at only one end. 
     As can be seen in FIG. 8, when viewed in the same plane as center line  102 , axes  33   a  of the aforesaid rocker arm shafts  33  form virtually right angles with axes  14   a   1  and  14   b   1  of intake valve  14   a  and exhaust valve  14   b.    
       31  is the rocker arm for the intake valve;  31 ′ is the rocker arm for the exhaust valve. They are arranged symmetrically with respect to the center line  102  of the cylinder. The tubular portions in their centers are inserted into the aforesaid rocker arm shafts  33  in such a way that the arms are free to swing and their movement in the axial direction can be controlled. 
     The aforesaid axes  33   a  of rocker arm shafts  33  are surrounded by the aforesaid rocker arm  31  for the intake valve and  31 ′ for the exhaust valve. Their ends  31   b  and  31   ′b  come in contact with push rods  15 . Their other ends,  31   c  and  31   ′c,  come in contact with intake valve  14   a  and exhaust valve  14   b .    
     Adjustment screws  24  on ends  31   b  and  31   ′b  are used to adjust the clearance of the valve operating mechanism. The rocker arms are engaged with push rods  15  through the spherical bearings on the ends of the adjustment screws. 
     The aforesaid ends  31   c  and  31   ′c  are in contact with intake valve  14   a  and exhaust valve  14   b  through straps  26   a . All other aspects of the configuration are identical to that of the second preferred embodiment shown in FIGS. 4 through 6. Components which are the same have been given the same numbers. 
     In this preferred embodiment, just as in the aforesaid first and second preferred embodiments, mounting surface  100  for the locker arm supporting base on the top of cylinder head  8  is either coplanar with top surface  101  on top of peripheral wall  8   c , to which head cover  9  is mounted, or slightly higher than that top surface. This design means that the two surfaces can be processed in a single stage, and the number of required processes is reduced. 
     In addition, just as in the aforesaid second preferred embodiment, rocker arm supporting base  32  is smaller and the area of the said mounting surface  100  can be smaller than in the aforesaid first preferred embodiment. Rocker arms  31  and  31 ′ can be made smaller, and the processing of the said mounting surface  100  is further simplified. In regard to configuration, the length of rocker arms  31  and  31 ′ can be increased, which prevents excessive force from being exerted in the valve operating mechanism. 
     Furthermore, in this third preferred embodiment, axes  33   a  of rocker arm shafts  33  are inclined at angles α 1  and α 2 . The points at which ends  31   b  and  31   ′b  of the arms for valves  14   a  and  14   b  are engaged with push rods  15  (i.e., the centers of adjustment screws  24 ) and the points at which ends  31   c  and  31   ′c  are in contact with the heads of valves  14   a  and  14   b  (i.e., the centers of straps  26   a ) fall on lines  50  and  50 ′, as can be seen in FIG.  7 . There is no deviation along axes  33   a  of the rocker arm shafts between the aforesaid points where the arms are engaged with the push rods and the points where they are in contact with the valves. Thus there is no moment generated in rocker arms  31  and  31 ′, and no excessive force experienced by the rocker arms due to moment. 
     We shall explain the fourth preferred embodiment of this invention in detail with reference of FIG.  10  through FIG.  17 . This fourth preferred embodiment is a modification on the lubrication device for the overhead combustion engine (OHV engine) shown in the first through third preferred embodiments. The OHV engine which this fourth preferred embodiment of the invention is applied is shown in FIG.  10 . 
     As can be seen in FIG. 10, the multipurpose four-cycle OHV engine in which this fourth preferred embodiment of the invention is employed has a cylinder head  8  with a pent-roof combustion chamber  1 , in which one intake valve  14   a  and one exhaust valve  14   b  are arranged so that their center lines radiate symmetrically. 
     In FIGS. 10 through 12,  2  is the cylinder;  5  is the crankshaft;  6  is the connecting rod;  7  is the piston;  8  is an aluminum die cast cylinder head with a pent-roof combustion chamber  1 .  9  is the head cover, which is mounted on top surface of the said cylinder head  8 .  14  and  14   a  are the intake and exhaust valves, arranged symmetrically in radiating fashion in the aforesaid cylinder head  8 . 
       15  are the push rods;  32  is the push rod chamber for the push rods;  16  are the tappets;  18  are the valve springs for the aforesaid intake and exhaust valves  14   a  and  14   b ;  19  are the spring retainers which transmit to the aforesaid intake and exhaust valves  14  and  14   a  the force of the said valve springs  18 ;  21  is the rocker arm for the intake valve;  21 ′ is the rocker arm for the exhaust valve, which is arranged so that it is symmetric with the aforesaid rocker arm  21 ;  22  is the rocker arm supporting base which supports the rocker arm shafts;  23  are two parallel rocker arm shafts. Valve operating mechanism  74  comprises components  14 ,  14   a ,  15 ,  16 ,  18 ,  19 ,  21 ,  21 ′,  22 ,  23  and cams  17   a.    
     The aforesaid rocker arm supporting base  22  is mounted to cylinder head  8  by means of four bolts  25 . The aforesaid parallel rocker arm shafts  23  are supported at two points in the axial direction. Tubular rocker arm  21 , the arm for the intake valve, and rocker arm  21 ′, the arm for the exhaust valve, are fixed along their axes to the aforesaid rocker arm shafts  23  so that they are symmetric with respect to the axes of the shafts and they are free to rotate. On one end of the aforesaid rocker arms  21  and  21 ′ are first arms  21   b  and  21   ′b,  which are pushed by the aforesaid push rods  15 . On the other end are second arms  21   c  and  21   ′c,  which operate intake and exhaust valves  14   a  and  14   b.    
     Adjusting screws  24 , which are used to adjust the clearance of valve operating mechanism  74 , are screwed into the ends of the aforesaid second arms  21   c  and  21   ′c.  On the ends of the said screws  24  are spherical bearings (not pictured) which receive the spherical ends of the aforesaid push rods  15 . Hemispherical washers  21   a  which are made of a material highly resistant to be worn away, are mounted on the ends of the aforesaid arms  21   c  and  21   ′c  which come in contact with the aforesaid intake and exhaust valves  14   a  and  14   b.    
     The mounting surface of the aforesaid cylinder head  8  on which the aforesaid rocker arm supporting base  22  for the rocker arm shafts is mounted and the top surface on which head cover  9  is mounted, which are identified in FIG. 12, are coplanar. In other words, they constitute a single surface. 
     When this OHV engine runs, the aforesaid valve operating mechanism  74  works in the following way. The rotational speed of crankshaft  5  is reduced by half by a timing gear (not pictured) and transmitted to camshaft  17 , on which cam  17   a  is mounted. With the help of tappets  16 , push rods  15  and rocker arms  21  and  21 ′, cam  17  opens and closes the aforesaid intake and exhaust valves  14   a  and  14   b  at a previously determined timing. 
     The aforesaid rocker arms  21  and  21 ′ are supported by shafts  23 . They swing back and forth in a see-saw motion, and the back-and-forth travel of the aforesaid push rods  15  is conveyed to intake and exhaust valves  14   a  and  14   b . The aforesaid valve springs  18  accurately transmit the stroke of cam  17   a  to the intake and exhaust valves. This means that a powerful force (a fixed load) is exerted in the direction in which valves  14   a  and  14   b  close. 
     This is why the aforesaid rocker arms  21  and  21 ′ have the aforesaid rocker arm shafts  23 , which have a relatively large diameter in order to be sufficient to withstand the powerful force from the valve spring. When the OHV engine is working, cylinder  2  and cylinder head  8  undergo thermal expansion. To prevent the components of the aforesaid valve operating mechanism  74  which touch each other from experiencing excessive force, the specified clearance for the tappets must be set for the time when the engine is cool and it must be adjusted by turning the aforesaid screws  24  when the engine is assembled. 
     The detailed structure of the fourth preferred embodiment is shown in FIG.  13  through FIG. 17. 14 a  is the intake valve,  14   b  is the exhaust valve and  74  is the valve operating mechanism. The said operating mechanism  74  is enclosed in valve operating mechanism chamber  92 , which is formed from the upper chamber of cylinder head  8  and head cover  9 . It comprises the aforesaid rocker arm supporting base  22 ; rocker arm shafts  23 ; rocker arms  21  and  21 ′; adjustment screws  24 ; valve springs  18 ; push rods  15 ; tappets  16 ; and cam  17   a.    
       8   c  is the peripheral wall of the aforesaid cylinder head  8 . It also serves as the wall of the aforesaid valve operating mechanism chamber  92 . On the top of the head is a top surface  101  (see FIG.  12 ), on which head cover  9  is fixed (see FIG. 10) sandwiching gasket  93  (shown by hatched lines in FIG.  13 ). 
       8   t  are female screws which are drilled in four places on the top surface of the aforesaid peripheral wall  8   c  to fix head cover  9  to the cylinder head.  8 n are four female screws to fix the aforesaid rocker arm supporting base  22 .  8   d  is a cylindrical mounting post for the said rocker arm supporting base  22 .  8   e  is the female screw in which spark plug  51  (see FIG. 10) is mounted. 
       93   b  is a circular hole which is cut in the aforesaid gasket  93  for the aforesaid mounting post  8   m  to go through.  93   a  is the protruding segment of the said gasket  93 . Breather passage  95 , which will be discussed shortly, is cut in such a way that its top is covered by this segment. The said segment  93   a  is held in position when the aforesaid cylindrical mounting post  8   m  engages in the aforesaid circular hole  93   b . When the aforesaid rocker arm supporting base  22  is fixed to cylindrical mounting post  8   m,  the segment is prevented from slipping off the bottom of that post. 
     In FIG. 14,  8   f  is the spring retainer for one valve spring  18 , the spring for the aforesaid intake valve  14   a .  8   h  is the spring retainer for the other valve spring  18 , the spring for the aforesaid exhaust valve  14   b.    
       8   g  is a ring-shaped rib which is built up around the aforesaid spring retainer  8   f . This rib keeps the valve spring  18  for the aforesaid intake valve  14   a  in the proper position.  8   i  is another ring-shaped rib which is built up around the aforesaid spring retainer  8   h . This rib keeps the valve spring  18  for the aforesaid exhaust valve  14   b  in the proper position. 
     Square-sided groove  8   p , which will be discussed shortly, and oil guide washer plate  76  for the spring retainers is provided in ring-shaped rib  8   g  for the aforesaid intake valve and ring-shaped rib  8   i  for the exhaust valve. The groove and washer plates constitute tubular passages  8   p  (as shown in FIG.  15 ). 
       8   j  is a straight guide wall which is connected to post  8   m , the mounting post for the aforesaid rocker arm supporting base  22  for the rocker arm shaft bearings. This relatively thin wall stands in a straight line on the aforesaid mounting post  8   m  between intake valve  14  and exhaust valve  14   a  in the fashion that it approaches the aforesaid ring-shaped ribs  8   g  and  8   i . As can be seen in FIG. 15, the height of this wall is slightly less than the top surface  101  of the aforesaid peripheral wall  8   c.    
       94  is a breather passage. It goes vertically through cylinder head  8  and cylinder  2  and communicates with crankcase  112 . 
     As is shown in FIGS. 14 and 15, the upper end of the said breather passage  94  is opened facing opening  8 k on the outer side of rib  8   g , the positioning rib for valve spring  18  of intake valve  14   a . Through the said opening  8   k , the breather passage is opened toward valve operating mechanism chamber  92  for the valve operating mechanism. 
       8   p  is a square-sided groove formed on the upper surface of the aforesaid cylinder head which faces valve operating mechanism chamber  92 , or, the side of that valve operating mechanism chamber. A portion of rib  8   g , the positioning rib for the aforesaid intake valve  14   a , is cut away;  8   s  is the resulting opening. A plan view would show an S-shaped passage  8   p  going from spring retainer  8   f  for the intake valve toward spring retainer  8   h  for the exhaust valve. One end of the said square-sided groove  8   p  communicates with the aforesaid opening  8   k ; the other, as can be seen in FIG. 16, communicates with the space above center protrusion  8   u  in the center of the upper surface of cylinder head  8 . The passage is configured with an angle sufficient to cause one end portion near the central protrusion to be higher than another end portion. 
     In the small multipurpose OHV engine of this fourth preferred embodiment, the aforesaid square-sided groove  8   p  should ideally be 3 to 5 mm deep. 
     Breather passage  95 , then, goes from the aforesaid opening  8   k  through groove  8   p , over center protrusion  8   u  in the center of the head which is the base of the aforesaid straight guide wall  8   j . It makes use of the tunnel formed by the aforesaid straight guide wall  8   j  and the peripheral wall  8   a  of the cylinder head, which goes as far as spring retainer  8   h  of exhaust valve  14   a.    
     In FIGS. 13 through 17,  76  is the oil guide washer plate for the spring retainer for intake valve  14   a.    
     In FIGS. 17 ( a ) (a frontal view) and ( b ) (a plan view), the aforesaid oil guide washer plate  76  comprises washer portion  76   a , entrance portion  76   b  and exit portion  76   c . The said washer portion  76   a  engages within ring-shaped rib  8   g  near the aforesaid intake valve  14   a . When intake valve  14   a  is installed, the elastic force of valve spring  18  exerts downward pressure to the foresaid oil guide washer plate on spring retainer  8   f . The said entrance portion  76   b  and part of exit portion  76   c  jutting out through opening  8   s  of the foresaid ring-shaped rib  8   g  cover the opening  8   k  in the aforesaid breather passage  94  and the top of S-shaped groove  8   p . The gap between the end of the aforesaid straight guide wall  8   j  and peripheral wall  8   c  of cylinder head  8  is covered by the aforesaid exit portion  76   c.    
     The OHV engine in FIG. 10 according to the fourth preferred embodiment has a lubrication device for its valve operating mechanism which is functioned in the following way. As shown in FIG. 10, when it operates and piston  7  moves downward, the volume of space in crankcase  112  is reduced. The oil picked up by oil dipper  115  (as shown in FIG. 20) and suspended in crankcase  112  is forced by the air moving through the crankcase to go up to the direction shown by arrow D in FIG.  16  and arrow E in FIG.  15 . This suspended oil travels through breather passage  94  and goes as far as opening  8   k  in cylinder head  8 . 
     At this point the said suspended oil takes a horizontal turn, passes through S-shaped groove  8   p  and exits from its front end. It then travels through the aforesaid breather passage  95 , which is formed by straight guide wall  8   j  and peripheral wall  8   c  of cylinder head  8 , toward exhaust valve  14   b . A portion of the suspended oil which is moving forward is repulsed through the gap at the exit portion  76   c  of the aforesaid oil guide washer plate  76 , and it is blown, in an appropriate quantity, to intake valve  14   a . In this way the said valve  14  is lubricated. 
     As is stated above, in this fourth preferred embodiment, breather passage  95  comprises square-sided groove  8   m , which runs between spring retainer  8   f  for supporting the valve spring  18  of intake valve  14   a  in cylinder head  8  and spring retainer  8   h  for supporting the valve spring  18  of exhaust valve  14   b , and a tunnel-like passage. The said breather passage  95  communicates with breather passage  94 , which connects with crankcase  112 , via opening  8   k . Thus the oil suspended in crankcase  112  is supplied in a reliable fashion from intake valve  14   a  to exhaust valve  14   b  in valve operating mechanism chamber  92 . In this way a sufficient quantity of oil can be supplied not only to intake valve  14   a , but also to exhaust valve  14   b , which experiences conditions of intense heat. 
     Since this breather passage  95  can be formed by the design of the top surface of cylinder head  8  which faces valve operating mechanism chamber  92 , and gasket  93 , it does not require any specialized parts. This allows the parts count to be reduced.