US20060075979A1

US20060075979A1 - Cylinder head assembly with coupled valve assemblies

Info

Publication number: US20060075979A1
Application number: US11/246,637
Authority: US
Inventors: Barry Grant
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-10-07
Filing date: 2005-10-07
Publication date: 2006-04-13

Abstract

A cylinder head assembly includes a coupled valve assembly, wherein valves are coupled together such that they are simultaneously actuated via a single rocker arm, push-rod, lifter, lobe, and cam shaft. The cylinder head assembly may be used in conjunction with an engine or may replace a cylinder head of the engine to increase the valves in at least one cylinder without extensive modification of the engine structure. The coupled valve assembly includes a bridge having opposed ends, each having a lower surface in contact with a valve stem, and a rocker arm that is generally parallel to the bridge and engages the bridge to actuate the valves.

Description

CROSS REFERENCE

This application claims the benefit of co-pending provisional U.S. Patent Application 60/616,721, filed Oct. 7, 2004.

TECHNICAL FIELD

The present invention is generally related to reciprocating internal combustion engines and, more particularly, is related to a substitute cylinder head for mounting on an internal combustion engine.

BACKGROUND OF THE INVENTION

In a reciprocating internal combustion engine, the performance of the engine is a complex balance of competing and differing design characteristics. One way that an engine's performance can be enhanced is to improve the engine's ability to breathe, which requires improving the engine's ability to pass air and fuel into a cylinder and to pass exhaust gases out of the cylinder. Improving the engine's ability to pass air and fuel into a cylinder results in a greater performance improvement than improving the engine's ability to pass exhaust gases from the cylinder because it is typically more difficult to draw air and fuel into a cylinder than it is to push exhaust gases out of the cylinder.
Many conventional engines use a cylinder head that has a single inlet valve and a single exhaust valve per cylinder. Each valve is actuated by a rocker arm that is driven by the oscillatory motion of a lobe, lifter, and push-rod combination, where the push-rod oscillates up and down due to the lifter riding on the lobe of the cam shaft. When a valve is open gases flow through it. In the case of the inlet valve, these gases are air or an air/fuel mixture. In the case of the exhaust valve, these gases are exhaust gases.
There are various ways to design and control a single valve such that more gas passes by the valve when the valve is open. One design is to increase the diameter of the valve, but larger valves generally require more mass. Valves that have more mass require stiffer springs to bias the valve into its closed position than do valves that have less mass. Consequently, larger valves tend to degrade engine performance at high revolutions per minute (RPM) due to the increased mass.
Another way to increase the gas flow past an open valve is to hold the valve open longer. Typically, the length of time that a valve is open depends upon the shape of the lobe that is driving the valve. However, there are problems associated with having the valve open for a long period time. Generally, when valves are open for a long period of time, the engine does not run well at low RPMs.
Instead of using only one valve per cylinder for inlet or exhaust purposes, high performance engines typically use multiple inlet or exhaust valves per cylinder to improve the engine's performance. Generally, each of the valves is individually driven, meaning one lobe, lifter, and push-rod combination drives each rocker arm, which drives each valve. Each one of the multiple valves is usually of smaller mass than a single valve, and therefore the springs for the multiple valves may not be as stiff as the spring for a single valve. However, a disadvantage of engines that employ multiple inlet or exhaust valves per cylinder is that they generally use more parts, such as lifters, lobes and push-rods, than do engines that employ only one inlet and exhaust valve per cylinder. Consequently, the engine can be less reliable and require more maintenance because more parts can malfunction.
Fewer parts may be used in an engine having multiple inlet or exhaust valves by coupling the valves together via a bridge. In such an engine, a single lobe, lifter, and push-rod combination drives a single rocker arm which drives both valves in unison via the bridge. One problem with using coupled valves actuated via a bridge is that friction between the rocker arm and the bridge is likely to cause the bridge to wear. Furthermore, the rocker arm may apply an undesirable torque to the bridge that may prevent the valves from opening and closing properly.
Some owners of small-block Chevrolet engines or other standard original equipment manufacturer (OEM) engines would like to increase the engine's power output by adding a valve to a cylinder of the engine. However, this modification cannot be made economically at the present time, because the modification would require extensive re-working of the engine structure. Thus, a need exists for an improved cylinder head assembly that improves engine performance by increasing gas flow into or out of a cylinder. A need also exists for a replacement cylinder head assembly that can replace an OEM cylinder head assembly so as to add a valve to each cylinder, improving the existing engine's performance.

SUMMARY OF THE INVENTION

In a typical internal combustion piston engine, each valve of the engine is actuated via a single rocker arm, push-rod, lifter, and lobe. The lobe riding on the cam shaft transmits movement of the cam shaft to the lifter and push-rod, causing the rocker arm to actuate the valve. In such an engine, adding valves requires adding rocker arms, push-rods, lifters, and lobes, increasing the number of parts that could malfunction and require maintenance. Alternatively, multiple valves may be coupled to a bridge that is actuated via a single rocker arm, push-rod, lifter, and lobe combination. Such an engine uses fewer parts, but friction between the rocker arm and the bridge may wear the bridge, or the rocker arm may apply an undesirable torque to the bridge preventing the bridge from remaining properly aligned with the valve stems.
In embodiments disclosed below, a coupled valve assembly may be used to actuate multiple valves using a single rocker arm, push-rod, lifter, and lobe combination. The coupled valve assembly uses a bridge that has features to minimize wear to the bridge or transverse force on the bridge. In one embodiment, the couple value assembly may be added to an original equipment manufacturer (OEM) engine to increase the number of valves in a cylinder with minimal disruption to the engine structure. In another embodiment, the coupled valve assembly may be used in conjunction with an OEM engine such that multiple valves may be actuated using a single rocker arm that will not wear or torque the bridge.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
FIG. 1A is perspective view of a portion of an internal combustion engine with the manifold removed and showing one coupled valve assembly and one single valve assembly.
FIG. 1B is a perspective view of the valve assemblies of FIG. 1A shown in greater detail.
FIG. 2 is a side view of a portion of the internal combustion engine of FIG. 1.
FIG. 3 is a top view of a portion of the internal combustion engine of FIG. 1.
FIG. 4 is a perspective view of a bridge for a coupled valve assembly.
FIG. 5 is a perspective view of an embodiment of a roller for a coupled valve assembly.
FIG. 6 is another perspective view of the roller shown in FIG. 5.
FIG. 7 is a perspective view of another embodiment of a roller for a coupled valve assembly.
FIG. 8 is a top view of a portion of an internal combustion engine having two coupled valve assemblies.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now in more detail to the drawings, in which like numbers refer to the same parts in the several views, FIGS. 1A and 1B illustrate one embodiment of the invention featuring a coupled valve assembly 24 and a standard valve assembly 26. A portion of a reciprocating internal combustion engine 10 is illustrated, but will not be discussed in detail because reciprocating internal combustion engines are well-known in the art. As shown in FIG. 1A and FIG. 1B, the engine 10 includes an engine block 14 with at least one cylinder, and a cylinder head assembly 20. The cylinder head assembly 20 includes a cylinder head 22, one coupled valve assembly 24 actuated by rocker arm 28, and one standard single valve assembly 26 actuated using standard rocker arm 29. The cylinder head assembly 20 may be used to add additional valves to an existing engine 10 by replacing the cylinder head of the OEM engine with a new cylinder head assembly 20 containing the coupled valve assembly 24.
FIG. 2 shows one cylinder 16 within the engine block 14, with the piston of cylinder 16 not illustrated. The cylinder head 22 includes an intake manifold 12 and an exhaust manifold 18. Bolts that are not illustrated are used to mount the intake manifold 12 and exhaust manifold 18 to the cylinder head 22, and to mount the cylinder head 22 to the engine block 14.
FIG. 2 also shows a coupled valve assembly 24. Each coupled valve assembly 24 includes a pair of valves 30A and 30B, a bridge 32, a rocker arm 28, and a base 64. Valve 30A has a corresponding disc 34A, a stem 36A that extends upward from the disc 34A, a plate 40A that is removably coupled to the valve 30A at its stem end 42A, and a spring 38A. The spring 38A engages the plate 40A and the cylinder head 22, biasing the plate 40A and valve 30A upwardly so that disc 34A moves to a closed position. Valve 38B functions in a like manner with respect to its disc 34B, stem 36B, stem end 42B, plate 40B, and spring 38B.
Referring to FIG. 4, the bridge 32 of the coupled valve assembly 24 includes an upper platform 46, opposed ends 44A and 44B, retaining walls 48A and 48B, and lower surfaces 50A and 50B. Retaining wall 48A is U-shaped and extends along the sides and the end of bridge 32 from upper platform 46 past lower surface 50A, enclosing opposed end 44A. The retaining wall 48A forms a cavity 96A that receives the valve stem end 42A of valve 30A. Retaining walls 48B is similarly configured to extend along the sides and the end of bridge 32 from upper platform 46 past lower surface 50B, enclosing opposed end 44B. The retaining wall 48B forms a cavity 96B that receives the valve stem end 42B of valve 30B. The lower surfaces 50A and 50B at the opposed ends 44A and 44B are positioned in the cavities 96A and 96B, and are substantially flat with a slight convex radius of curvature. The upper platform 46 may be substantially flat as shown in FIG. 4. In an alternate embodiment shown in FIG. 7, the upper platform 46 may have a groove 88 running along its length.
Referring to FIG. 2, cavities 96A and 96B of opposed ends 44A and 44B fit over the valve stem ends 42A and 42B of valves 30A and 30B. The stem ends 42A and 42B contact the lower surfaces 50A and 50B somewhere along the slight radius of curvature, inside the cavities 96A and 96B created by the retaining walls.
Referring to FIG. 2, the coupled valve assembly 24 further includes a rocker arm 28 and a base 64 that is mounted on the cylinder head 22. The rocker arm 28 defines an elongated body having a cam end 66 and a bridge end 68. The rocker arm 28 is pivotally coupled to the base 64 such that the cam end 66 and bridge end 68 can oscillate up and down. The bridge end 68 includes a roller 70 that is attached to the bridge end 68 via an axle 72. The roller 70 illustrated in FIG. 2 is a cylindrical roller. A push-rod recess 74 is formed in the underside of the cam end 66.
FIGS. 5 and 6 illustrate one embodiment of a roller 70 that may be used in conjunction with the coupled valve assembly 24. The roller 70 has a cylindrical body 90 that is at least as wide as the upper platform 46. The cylindrical body 90 is sandwiched between two disc-shaped flanges 92A and 92B that have a slightly larger radius than the cylindrical body 90. The cylindrical body 90 contacts the upper platform 46 of bridge 32, while the flanges 92A and 92B extend past and straddle the upper platform 46. The flanges 92A and 92B maintain the roller 70 aligned with the upper platform 46 of the bridge 32.
FIG. 7 illustrates an alternate embodiment of roller 70 that may be used in conjunction with a bridge 32 having a concave groove 88. The roller 70 has a cylindrical body 90 with a convex annular protrusion 94. The annular protrusion has a radius of curvature complementary to the radius of curvature of the groove 88. The annular protrusion 94 maintains the roller 70 aligned with the groove 88 on the upper platform 46 of the bridge 32.
Referring again to FIG. 2, the engine 10 also includes a cam shaft 76 having a lobe 78 and a lifter 80. Each lifter 80 rides on the periphery of the lobe 78 as the cam shaft 76 rotates. A push-rod 82 extends from the lifter 80 to the push-rod recess 74 of the rocker arm 28.
The cylinder head assembly 20 illustrated in FIGS. 2-3 includes a coupled valve assembly 24 in conjunction with a single valve assembly 26. The single valve assembly 26 is a conventional valve assembly comprising a valve, having a disc and a stem, a spring, and a plate (not shown). Because the single valve assembly 26 is conventional, it is not discussed in detail.
Engine 10 has at least one intake duct 52 and at least one exhaust duct 54 in each cylinder 16, but each cylinder 16 may have more than one of either type of duct. The exhaust duct 54 is in pneumatic communication with the exhaust manifold 18. Exhaust gases from cylinder 16 are ported through the exhaust duct 54 by the opening and closing of the valve of the single valve assembly 26. Therefore, in this embodiment, the cylinder 16 has a single exhaust valve actuated via the single valve assembly 26.
Further, in FIG. 3, the inlet valves of cylinder 16 are valves 30A and 30B, shown in pneumatic communication with the intake duct 52 and the intake manifold 12. Therefore, in this embodiment, the cylinder 16 has coupled inlet valves actuated via the coupled valve assembly 24. For carbureted engines, an air-fuel mixture flows through the intake duct 52 into the cylinder 16 via the inlet valves. For fuel-injected engines, air flows from the intake duct 52 through the inlet valves and into the cylinder 16.
As shown in FIG. 2, the intake duct 52 has two valve openings 56A and 56B. Aligned with valve opening 56A is stem guide hole 58A which extends from the exterior of the cylinder head 22 to the intake duct 52. Stem guide hole 58A receives valve stem guide 60A, which extends through stem guide hole 58A into the intake duct 52. Disc 34A of valve 30A is seated in valve opening 56A with stem 36A extending upward from the disc 34A through the valve stem guide 60A, such that stem end 42A contacts the lower surface 50 of bridge 32. In a similar fashion, the stem 36B and stem end 42B of valve 30B pass through stem guide hole 56B and valve stem guide 60B and contact the lower surface 50 of bridge 32.
While the embodiment shown in FIGS. 2-3 shows the cylinder 16 with a single exhaust valve and coupled inlet valves, other embodiments will be readily apparent to a person having ordinary skill in the art. For example, FIG. 8 shows the cylinder head assembly 20 including two coupled valve assemblies 24, such that inlet valves are coupled together using a coupled valve assembly and the exhaust valves are coupled together using a coupled valve assembly. In such an embodiment, where coupled valve assemblies are used for both inlet and exhaust purposes, no single valve assembly 26 is required.

Operation

While each valve in a conventional engine requires its own rocker arm, push-rod, lifter, and lobe, the coupled valve assembly actuates multiple valves using a single rocker arm 28, push-rod 82, lifter 80, and lobe 78, which in turn cause valves 30A and 30B to remove from and return to their valve openings 56A and 56B. As the cam shaft 76 rotates such that the lobe 78 moves upward, the lifter 80 rides over the lobe 78 causing the lifter 80 to rise. The motion of the lifter 80 causes the push-rod 82 to reciprocate upwardly. The upward motion of the push-rod 82 causes the cam end 66 of the rocker arm 28 to be raised, thereby causing the bridge end 68 to be lowered. As the bridge end 68 lowers, the roller 70 travels along the upper platform 46 of the bridge 32, pushing the bridge 32 downward. Path 86, shown in FIG. 3, denotes the path traveled by roller 70 as it pushes on the bridge 32. The bridge 32 in turn pushes the valves 30A and 30B downwardly, which displaces the discs 34A and 34B from their respective valve openings 56A and 56B. Gas from a duct may then flow through open valves 30A and 30B into the cylinder 16. For example, in the embodiment shown in FIG. 2, gas from intake duct 52 flows through valves 30A and 30B when open.
As the lifter 80 rides down the lobe 78, the springs 38A and 38B bias their valves 30A and 30B to the closed position, which closes the cylinder 16 from the duct. The springs 38A and 38B also respectively engage plates 40A and 40B to return the bridge 32 and the bridge end 68 of the rocker arm 28 to their upward positions. In this manner, the rotation of cam shaft 76 causes the rocker arm 28 to pivot about the base 64 such that the valves are removed from and returned to their openings 56A and 56B. Arc 84, shown in FIG. 2, denotes the vertical path of the bridge end 68 in response to the oscillation of the rocker arm 28.
As the rocker arm 28 oscillates about the base 64, the rocker arm 28, bridge 32, and valves 30A and 30B should remain in general alignment so that the valves create an effective seal between cylinder 16 and the duct. For this reason, the rocker arm 28 and bridge 32 are designed to minimize the creation and transfer of transverse force from the rocker arm 28 to the bridge 32 and from the bridge 32 to the valve stem ends 42A and 42B. Otherwise, the transverse force on the valve stem ends 42A and 42B might inhibit discs 34A and 34B from aligning with openings 56A and 56B, affecting the seal between the cylinder 16 and the duct.
The rocker arm 28 contacts the bridge 32 using a roller 70 to minimize transverse force applied to the bridge 32. As roller 70 contacts bridge 32, it travels a path 86 that is parallel to the length and bisects the width of upper platform 46, as shown in FIG. 3. The location of the path 86 limits transverse force applied by the roller 70 to the bridge 32.
To further minimize transverse force on the bridge 32, the rocker arm 28 and the bridge 32 are generally aligned as shown in FIG. 3. In some embodiments, the roller 70 includes features to retain the bridge 32 in alignment with the rocker arm 28. For example, FIG. 6 shows the roller 70 with cylindrical flanges 92A and 92B that extend along the sides of the upper platform 46. As the roller 70 travels along the upper platform 46, the cylindrical flanges 92A and 92B keep the bridge 32 aligned with the rocker arm 28. In another embodiment, as shown in FIG. 7, the roller 70 has an annular protrusion 94 and the bridge 32 has a groove 88. As the roller travels along the upper platform 46, the groove 88 engages the annular protrusion 94 to retain the bridge 32 in alignment with the rocker arm 28.
If the rocker arm 28 does apply a transverse force to the bridge 32, the bridge 32 and the valve stems 36A and 36B remain in general alignment, because the valve stems ends 42A and 42B are free to travel along the bridge's lower surfaces 50A and 50B. The bridge 32 contacts valve stem end 42A somewhere along the portion of the lower surface 50A at opposed end 44A having a concave radius of curvature. The radius of curvature ensures that the longitudinal center axis of valve stem 36A remains perpendicular to a plane that is tangential to the point of contact between the valve stem end 42A and the lower surface 50A. Therefore, valve stem 36A moves in the plane of motion of the rocker arm 28. Similarly, the bridge 32 contacts valve stem end 42B somewhere along the portion of lower surface 50B at opposed end 48B having a concave radius of curvature, ensuring the plane of motion of valve stem 36B is parallel to the plane of motion of rocker arm 28.
Because valve stem ends 42A and 42B have freedom to travel along the lower surfaces 50A and 50B of bridge 32, transverse force on the bridge or any other disturbance in the system may cause bridge 32 to slip off of valve stem ends 42A and 42B. For this reason, retaining walls 48A and 48B create cavities 96A and 96B that enclose valve stem ends 42A and 42B. Bridge 32 is therefore retained on the valve stem ends 42A and 42B.
The roller 70 also minimizes friction between the rocker arm 28 and the bridge 32. Therefore, the bridge 32 is less likely to require replacement due to wear.
As is mentioned above, it is often desirable to increase the power output of an engine by increasing the number of inlet valves in cylinders of the engine. However, such a modification often requires extensive re-working of the engine. For example, a cylinder head having one inlet valve and one exhaust valve per cylinder may have a push-rod, lifter, and lobe for each valve. Adding inlet valves may require engine modification because additional lobes, lifters, and push-rods must be added to the engine to actuate the new valves. However, the cylinder head assembly 20 may be used to replace the cylinder head of the engine, adding valves to the engine without modifying it.
The cylinder head assembly 20 may be built to conform to any engine architecture, so that the cylinder head assembly 20 may be connected to the engine after the cylinder head of the engine is removed. However, the cylinder head assembly 20 also contains at least one coupled valve assembly 24 that allows two valves to be actuated via a single rocker arm, push-rod, lifter, and lobe combination. By removing the engine's cylinder head of the engine and replacing it with the cylinder head assembly 20 containing at least one coupled valve assembly 24, additional valves may be added to the engine that are actuated via the engine's parts. When the additional valves are inlet valves, the power output of the engine will likely increase as a result of increased flow into the cylinder.
In one embodiment, the replacement cylinder head assembly 20 is adapted to fit onto a “small block” Chevrolet engine, which is a V8-engine with 16 valves. The horsepower of the engine may be increased by removing the OEM cylinder head and replacing it with the replacement cylinder head assembly 20 that contains coupled valves inlet valves 30A and 30B driven by a single lobe 78 on the cam shaft 76. Consequently, inlet valves may be added without increasing the number of lobes, lifters, and push-rods over the number used in the OEM engine.
In many embodiments, the cam, lobes, lifters, and push-rods of the engine may be used with the cylinder head assembly 20. In some embodiments, the push-rod 82 of the engine 10 may be replaced with a replacement push-rod of a different length to compensate for the change in height between the cylinder head 22 and the rocker arm 28. In embodiments where the push-rod 82 is replaced, the replacement push-rod will engage the lifter 80 in substantially the same manner as the replaced push rod, but the replacement push-rod itself will be slightly longer in length. Note, however, that replacing the push-rod 82 does not affect the two-to-one relationship between the valves 30A and 30B and the push-rod 82.
In other embodiments, the cylinder head assembly 20 may be implemented originally on an engine. Using at least one coupled valve assembly 24 enables an engine manufacturer to produce an engine 10 having the performance characteristics associated with multiple inlet and/or exhaust valves without an independent driving mechanism for each valve. Thus, the manufacturer may reduce the number of lobes, lifters and push-rods using a coupled valve assembly 24.
Those skilled in the art will recognize that in alternative embodiments the rocker arm 28 may be driven by an overhead cam where the cam shaft 76 is above the cylinder head 22 instead of beneath it.
It should be emphasized that the above-described embodiments, particularly any preferred embodiments, are merely possible examples of implementations set forth for a clear understanding of the present disclosure. Variations and modifications may be made to the above-described embodiments without departing from the spirit and principles of the disclosure. All such modifications and variations are intended to be included within the scope of this disclosure and to be protected by the following claims.

Claims

1. A valve-coupling assembly for coupling two valves, each having a valve stem and a valve stem end, to a single cam-shaft, lobe, lifter, and push-rod of an engine, the assembly comprising:

a bridge comprising,

an upper platform, and

opposed ends, each opposed end having a lower surface, and each lower surface having a contact point in contact with a valve stem end, the position of the contact point changing as the valve stem end moves on the lower surface, wherein the opposed end is configured to retain the valve stem end in contact with the lower surface and the lower surface is configured to maintain the valve stem in perpendicular alignment with a plane tangential to the contact point; and

a rocker arm pivotally connected to the engine and engaging the push-rod and the upper platform of the bridge,

such that when the cam shaft, lobe, and lifter of the engine raise the push-rod, the rocker arm pivots to lower the bridge which concurrently lowers the valve stems.

2. The valve-coupling assembly of claim 1, wherein each lower surface has a convex radius of curvature, and wherein each opposed end has a three-sided retaining wall that extends from the upper platform past its lower surface.

3. The valve-coupling assembly of claim 1, wherein the rocker arm comprises a cylindrical roller in contact with the upper platform of the bridge such that as the rocker arm pivots the roller travels along the upper platform of the bridge.

4. The valve-coupling assembly of claim 3, wherein the roller travels along a line on the upper platform that extends along the length and bisects the width of the upper platform.

5. The valve-coupling assembly of claim 4, wherein the roller is configured to maintain the rocker arm in parallel alignment with the bridge.

6. The valve-coupling assembly of claim 5, the upper platform further comprising a concave groove that extends along the length of the upper platform, and the roller further comprising a convex annular protrusion, wherein the annular protrusion engages the groove as the roller travels along the upper platform to maintain the rocker arm and the bridge in parallel alignment.

7. The valve-coupling assembly of claim 5, further comprising a cylindrical flange on each side of the cylindrical roller, wherein each cylindrical flange extends past the upper platform to maintain the bridge in parallel alignment with the rocker arm as the roller travels along the upper platform.

8. A replacement cylinder head assembly for a reciprocating piston internal combustion engine, the engine having an engine block, a cylinder head, a cam shaft, a lobe, a lifter and a push-rod, the replacement cylinder head assembly used for adding a valve to a cylinder of the engine by replacing the cylinder head of the engine with the replacement cylinder head assembly, the replacement cylinder head assembly comprising:

a replacement cylinder head, configured to function in substantially the same manner as the cylinder head of the engine, and configured to engage the engine block in substantially the same manner as the cylinder head of the engine such that the replacement cylinder head may be added to the engine block without altering the engine block, the replacement cylinder head comprising,

a replacement valve opening, and

a new valve opening;

one coupled valve assembly for the new valve opening, the coupled valve assembly comprising,

coupled valves, including a replacement valve for the replacement valve opening and a new valve for the new valve opening, wherein each valve has a valve stem and a disc that fits within the valve opening,

a rocker arm pivotally connected to the replacement cylinder head and engaging the push-rod, and

a bridge engaging the rocker arm and the valve stems, wherein the bridge is configured to maintain the valve stems in parallel alignment with the plane of motion of the rocker arm,

such that when the cam shaft, lobe, and lifter of the engine raise the push-rod, the rocker arm pivots to lower the bridge, which lowers each valve from its valve opening.

9. The replacement cylinder head assembly of claim 8, wherein the bridge comprises:

an upper platform, and

opposed ends, each opposed end having a lower surface, and each lower surface having a contact point in contact with a valve stem end, the position of the contact point changing as the valve stem end moves on the lower surface, wherein the opposed end is configured to retain the valve stem end in contact with the lower surface and the lower surface is configured to maintain the valve stem in perpendicular alignment with a plane tangential to the contact point.

10. The replacement cylinder head assembly of claim 9, wherein each lower surface has a convex radius of curvature, and wherein each opposed end has a three-sided retaining wall that extends from the upper platform past its lower surface.

11. The replacement cylinder head assembly of claim 9, wherein the rocker arm comprises a cylindrical roller in contact with the upper platform of the bridge such that as the rocker arm pivots the roller travels along the upper platform of the bridge.

12. The replacement cylinder head assembly of claim 11, wherein the roller travels along a line on the upper platform that extends along the length and bisects the width of the upper platform

13. The replacement cylinder head assembly of claim 12, wherein the roller is configured to maintain the rocker arm in parallel alignment with the bridge.

14. The replacement cylinder head assembly of claim 13, the upper platform further comprising a concave groove that extends along the length of the upper platform, and the roller further comprising a convex annular protrusion, wherein the annular protrusion engages the groove as the roller travels along the upper platform to maintain the rocker arm and the bridge in parallel alignment.

15. The replacement cylinder head assembly of claim 13, further comprising a cylindrical flange on each side of the cylindrical roller, wherein each cylindrical flange extends past the upper platform to maintain the bridge in parallel alignment with the rocker arm as the roller travels along the upper platform.

16. A kit for replacing the cylinder head of a reciprocating internal combustion engine, the engine having an engine block, a cylinder head, a cam shaft, a lobe, a lifter and a push-rod, the kit comprising:

a replacement inlet valve opening, and

a new inlet valve opening;

one coupled valve assembly for the new inlet valve opening, the coupled valve assembly comprising:

coupled valves, including a replacement valve for the replacement inlet valve opening and a new valve for the new inlet valve opening, wherein each valve has a valve stem and a disc that fits within the valve opening,

a rocker arm pivotally connected to the replacement cylinder head, and

a bridge engaging the rocker arm and the valve stems, wherein the bridge is configured to maintain the valve stems in parallel alignment with the plane of motion of the rocker arm;

a replacement push-rod for each coupled valve assembly, engaging the lifter and the rocker arm; and

at least one standard exhaust valve assembly, wherein the standard value assembly comprises a standard exhaust valve actuated using a standard rocker arm.

17. A method of delivering a fuel and air mixture to an internal combustion piston engine, comprising:

placing a bridge having its ends in contact with the stems of adjacent valves,

urging the bridge downwardly at a position between the ends of the bridge with a roller to open the valves,

rolling the roller along the length of the bridge as the roller urges the bridge downwardly, and

maintaining the roller aligned on the bridge with protrusions extending from the roller.