Patent Abstract:
The invention is a decompression kit for large bore and/or high compression internal combustion engines. Specifically designed for engines such as the “Harley-Davidson®” “V-Twin®” or the “Sportster®” models, the invention vents high cylinder pressure and reduces the associated high starter torque required to turn the crankshaft when starting the engine, this in turn reduces the cranking amperage necessary to start the engine resulting in longer starter and battery life. A modified spark plug, steel tubing, and decompression valves are the main components of the invention. Cylinder pressure during the compression stroke is vented through the spark plug, tubing, and the decompression valve to make starting the engine easy.

Full Description:
RELATED APPLICATIONS 
     There are no previously filed, nor currently any co-pending applications, anywhere in the world. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to decompression devices for internal combustion engines and, more particularly, to an aftermarket cylinder decompression device for motorcycle engines for activation during engine start up and the method for making same. 
     2. Descridption of the Related Art 
     Internal combustion engines and other high compression engines require a large cranking torque in order to start the engine. This can be especially difficult during cold starts. The large amount of cranking torque required places a great strain on starter motor and battery life often resulting in premature failure. 
     Various mechanism have been developed in order to provide compression relief during starting such as relief valves, decompression ports, and decompression slots formed in the walls of the cylinder. These devices vent a portion of the internal cylinder pressure during the compression stroke during startup in internal combustion engines thereby reducing the amount of torque needed to turn the crankshaft during start up. 
     In the related art, there exists patents for devices of this type for two-cycle engines. Typically, these devices are integrally built into the engine and there exists many attempts to engage the device upon startup by tying it to the starter recoil mechanism or via operator actuated means. However, no patents exist in the art for an aftermarket engine cylinder decompression device that can be used with many types of engines, particularly four-stroke motorcycle engines. Also, it is not always desirable to have the decompression device activated and devices of this type cannot be deactivated. 
     A search of the prior art did not disclose any patents that read directly on the claims of the instant invention; however, the following references were considered related: 
     
       
         
               
               
               
             
           
               
                   
               
               
                 U.S. Pat. No. 
                 Inventor 
                 Issue Date 
               
               
                   
               
             
             
               
                 5,799,635 
                 Aljabari 
                 Sep 1, 1998 
               
               
                 3,687,124 
                 Kolorz 
                 Aug. 29, 1972 
               
               
                 5,701,860 
                 Horiuchi et al. 
                 Dec. 30, 1997 
               
               
                 5,582,143 
                 Stark et al. 
                 Dec. 10, 1996 
               
               
                 5,379,734 
                 Tsunoda et al. 
                 Jan. 10, 1995 
               
               
                 5,361,738 
                 Iida 
                 Nov. 8, 1994 
               
               
                 5,116,287 
                 Hironaka et al. 
                 May 26, 1992 
               
               
                 5,687,683 
                 Knoblauch 
                 Nov. 18, 1997 
               
               
                 4,394,851 
                 Greier et al. 
                 Jul. 26, 1983 
               
               
                 4,184,468 
                 Freyn 
                 Jan. 22, 1980 
               
               
                 5,630,385 
                 Taomo 
                 May 20, 1997 
               
               
                 5,377,642 
                 Morrow et al. 
                 Jan. 3, 1995 
               
               
                 4,993,372 
                 Mott et al. 
                 Feb. 19, 1991 
               
               
                   
               
             
          
         
       
     
     Consequently, a need has been felt for providing an aftermarket motorcycle engine decompression device for use during engine startup. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an improved motorcycle engine decompression valve to reduce the amount of torque required at engine startup. 
     It is another object of the present invention to provide an aftermarket motorcycle engine decompression valve that can used with virtually any motorcycle engine. 
     It is yet another object of the present invention to reduce the possibility of engine lock up during start up. 
     It is yet still another object of the present invention to preserve battery and starter motor life on electric start motorcycles. 
     It is still yet another object of the present invention to be operator activated only as required. 
     It is a benefit of the present invention that no disassembly of the motorcycle engine or machine shop work is required to install. 
     It is an advantage of the present invention it is easily installed at a relatively small cost. 
     Briefly described according to one embodiment of the present invention, provided is a decompression kit for large bore and/or high compression internal combustion engines. Specifically designed for engines such as the “Harley-Davidson®” “V-Twin®” or the “Sporster®”, the device vents high cylinder pressure and the associated high torque required to turn the crankshaft when starting the engine. The device also minimizes the possibility of dangerous kick back of the kick starter during manual starts. A modified spark plug, steel tubing, and decompression valves are the main components of the invention. Cylinder pressure during the compression stroke is vented through the spark plug, tubing, and the decompression valve to make starting the engine easy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages and features of the present invention will become better understood with reference to the following more detailed description and claims taken in conjunction with the accompanying drawings, in which like elements are identified with like symbols, and in which: 
     FIG. 1 is a partially cutaway view of motorcycle engine having a decompression valve installed, according to the preferred embodiment of the present invention; 
     FIG. 2 is a partially cutaway exploded view of motorcycle engine and the decompression valve removed from the spark plug socket, according to the preferred embodiment of the present invention; 
     FIG. 3 is a partial cutaway cross sectional view taken along I—I of FIG. 1 with the decompression valve installed, according to the preferred embodiment of the present invention; 
     FIG. 4 is a front view of a decompression valve for a motorcycle engine such as the “Harley-Davidson®” “V-Twin®”, according to the preferred embodiment of the present invention; 
     FIG. 5 is a front cross sectional view taken along line IV—IV of FIG. 4 of a decompression valve for a motorcycle engine such as the “Harley-Davidson®” “V-Twin®”, according to the preferred embodiment of the present invention; 
     FIG. 6 a  is an exploded front view of the relief valve, valve base, tubing and gas port chamber from a decompression valve for a motorcycle engine such as the “Harley-Davidson®” “V-Twin®”, according to the preferred embodiment of the present invention; 
     FIG. 6 b  is a side view of the gas port chamber from a decompression valve for a motorcycle engine such as the “Harley-Davidson®” “V-Twin®”, according to the preferred embodiment of the present invention; 
     FIG. 6 c  is a top view of the gas port chamber from a decompression valve for a motorcycle engine such as the “Harley-Davidson®” “V-Twin®” showing the detail of the aperture formed in the center, according to the preferred embodiment of the present invention; 
     FIG. 6 d  is a bottom view of the gas port chamber from a decompression valve for a motorcycle engine such as the “Harley-Davidson®” “V-Twin®” showing the detail of second hole partially drilled in the bottom forming a lip and gas collection chamber, according to the preferred embodiment of the present invention; and 
     FIG. 7 is a front view of a modified spark plug as part of and used in conjunction with a decompression valve for a motorcycle engine such as the “Harley-Davidson®” “V-Twin®”, according to the preferred embodiment of the present invention. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 LIST OF REFERENCE NUMBERS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 5 
                 motorcycle engine 
               
               
                   
                 6 
                 cylinder 
               
               
                   
                 7 
                 piston 
               
               
                   
                 8 
                 piston rod 
               
               
                   
                 9 
                 crankshaft 
               
               
                   
                 10 
                 cylinder walls 
               
               
                   
                 11 
                 cylinder head 
               
               
                   
                 12 
                 combustion chamber 
               
               
                   
                 13 
                 intake valve 
               
               
                   
                 14 
                 exhaust valve 
               
               
                   
                 15 
                 spark plug port 
               
               
                   
                 20 
                 decompression valve assembly 
               
               
                   
                 21 
                 relief valve 
               
               
                   
                 21a 
                 plunger 
               
               
                   
                 21b 
                 valve base 
               
               
                   
                 22 
                 tubing 
               
               
                   
                 23 
                 gas port chamber 
               
               
                   
                 23a 
                 vent aperture 
               
               
                   
                 23b 
                 plug aperture 
               
               
                   
                 23c 
                 lip 
               
               
                   
                 23d 
                 chamber area 
               
               
                   
                 24 
                 spark plug 
               
               
                   
                 24a 
                 threaded base 
               
               
                   
                 24b 
                 aperture 
               
               
                   
                 24c 
                 slot 
               
               
                   
                 24d 
                 dielectric 
               
               
                   
                 24e 
                 electrode 
               
               
                   
                   
               
             
          
         
       
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The best mode for carrying out the invention is presented in terms of its preferred embodiment, herein depicted within the FIGS. 
     1. Detailed Description of the Figures 
     Referring now to FIGS. 1 and 2, a decompression valve  20  for large bore and/or high compression internal combustion motorcycle engines is shown, according to the present invention, particularly for the “Harley-Davidson®” “V-Twin®”(shown in FIG. 1) or the “Sporster®”(not shown) models although it is envisioned the device  20  could be adapted to for use with virtually any internal combustion engine found in motorcycles, snowmobiles, go-karts, chain saws, lawn mowers, etc. The device  20  is essentially a modified spark plug to be installed in the spark plug port  15  in place of the regular spark plug. A small slot (described further hereinbelow) is cut into the sidewall of the threaded base portion of the spark plug to allow cylinder pressure to escape to the exterior of the sidewall and where it is received in a gas chamber of a gas port that physically encapsulates the threaded portion of the spark plug between the base of the spark plug and the cylinder head. A small diameter tube connects the gas chamber to a valve that is physically located close to the spark plug and cylinder head. The valve allows a small amount of cylinder pressure to be released to the atmosphere when a plunger on the top is depressed. When the operator desires to start the engine the plunger on the top of the valve is depressed then the starter button is depressed until the engine starts. 
     Referring now to FIGS. 3 through 7, shown is the detail of the installation and operation of the device  20  for a motorcycle engine  5  as previously described. The specially modified spark plug  24  is installed in the conventional spark plug port  15  (shown in FIG.  2 ). The spark plug is a “hot” style which has an extended, threaded base  24   a  that normally protrudes further into the cylinder  6  when installed for higher combustion temperatures. The extended thread base  24   a  allows the installation and function of the gas port chamber  23  when the device  20  is installed. When installed in this fashion, the spark plug  24  functions as a normal spark plug. Referring specifically now to FIGS. 4 and 5, protruding from the side of gas port chamber  23  is vent tube  22  which consists of a short piece of formed or contoured steel tubing approximately two inches long, with a 0.180 inch outer diameter and 0.089 inch inner diameter. Gas port chamber  23  is connected to one end of vent tube  22 , and the opposite end is connected to valve base  21   b  of valve  21 . Valve  21  is a well known off the shelf component that can be obtained at a reasonable cost. All connections are welded or brazed. A valve plunger  21   a  normally biased in the closed position is located on the top of valve  21  for placing the interior chamber of valve  21  in fluid communication with the atmosphere. At final assembly, the modified spark plug  24  is placed through the gas port chamber  23  through the aperture  23   b  in the center and tightened in the spark plug port  15 . While cranking the engine, the motorcycle operator simply pushes valve plunger  21   a . Normally, as piston  6  travels upward (as depicted by the arrow in FIG. 3) air and fuel vapor are compressed to a high pressure in the combustion chamber  12  in preparation for ignition by spark plug  24 . These pressures can be extremely high causing excessive amounts of torque to continue forcing piston  7  upward as crankshaft  9  is turned at startup. To ease this difficulty and aid in starting, while cranking the engine over the motorcycle operator can release a small amount of this pressure from combustion chamber  12  by depressing valve plunger  21   a . The means whereby cylinder  6  pressure is vented to the atmosphere through gas chamber  23 , vent tube  22 , and valve  21  is described further hereinbelow. 
     Referring now specifically to FIGS. 6 a  through  6   d , the detail of the cooperation of gas port chamber  23  with vent tube  22  and valve  21  is shown. Vent tube  22  is connected at one end to the side of gas chamber  23  and in fluid communication with the interior chamber therein depicted in FIG. 6 b  as numeral  23   d . Vent tube  22  then is bent 90° upward and connected at the other end to the valve base  21   b  (not shown in this FIG.) being in fluid communication with the interior chamber defined therein. Preventing fluid communication of this interior chamber with the atmosphere is valve  21 . However, upon depressing valve plunger  21   a  downward, valve  21  is opened and vent tube  22  and hence the interior chamber  23   d  of gas port chamber  23  are placed in fluid communication with the atmosphere. 
     Gas port chamber  23  is essentially ring shaped with an aperture  23   b  drilled in the center. Gas port chamber can be manufactured from the same material as vent tubing  22 . The outer diameter of gas port chamber  23  and the diameter of aperture  23   b  necessarily will be different for different engine  5  models and manufacturers as well as different spark plugs used therewith. By way of example, for the “Harey-Davidson®” “V-Twin®” engine, the outer diameter of the gas port chamber  23  is 0.8 inch, aperture  23   b  is 0.550 inch. A second hole through the center of gas port chamber  23  is drilled with a diameter of 0.585 inch to a depth of 0.200 inch forming a lip  23   c  as can be seen in FIG. 6 d . The area created by drilling the 0.585 inch diameter in the lower portion of gas port chamber  23  is the actual chamber  23   d  wherein cylinder gas collects before being vented through vent tube  22 . When device  20  is installed, spark plug  24  is inserted through gas port chamber  23  and lip  23   c  faces downward facing the surface of cylinder wall  10  wherein spark plug port  15  is located. Chamber  23   d  then surrounds the upper portion of the threaded base  24   a  of spark plug  24 . For a “Sportster®” model engine, the dimensions of the gas port chamber  23  are 0.750 inch for the outer diameter, 0.469 inch diameter for aperture  23   b , 0.500 inch diameter for the second hole drilled to a depth of 0.200 inch to form chamber  23   d  and lip  23   c . Of course, these particular dimensions are for the models listed and in no way imply any limitation on any of the dimensions of the device  20 . 
     Referring now to FIG. 7, the modification to spark plug  24  involves drilling a 0.089 inch diameter hole, denoted as aperture  24   b  through the threaded base  24   a  so as to intersect the internal tapered surface of the dielectric material  24   d . This opens an airway from the inside of the spark plug  24  around the dielectric material  24   d  to the outside of the plug. This location is determined by using a 0.010 inch diameter wire gauge. The gauge is inserted into the electrode hole to find the depth to the tapered dielectric surface  24   d  (not shown in this FIG.), and consequently the location to drill a hole for forming slot  24   c .From this aperture  24   b , and extending toward the non-threaded area of threaded base  24   a , a 0.089 inch deep by 0.089 inch wide slot, denoted as slot  24   c ,is cut into threaded base  24 . The length of slot  24   c  is variable and depends upon the particular spark plug  24  manufacturer and the internal length of dielectric insulator  24   d . Slot  24   c  is used to direct, or channel, the gas vapor from aperture  24   b  in threaded base  24  into gas port chamber  23   d . The gas vapor is then forced through vent tube  22  and against valve  21 . (See FIG. 5) Compressed gas vapor, generated on the compression stroke, is forced through a minute aperture located on the side of valve  21 . A visible burst of vapor is expelled through this aperture away from valve  21 . When piston  7  reaches the ignition point in the cycle the additional expansion of gas closes valve  21 . 
     2. Operation of the Preferred Embodiment 
     To use the present invention, one simply removes the spark plug from the cylinder and replaces it with a modified spark plug. The spark plug threaded base is inserted through an aperture in the center of the gas port chamber. The upper portion of the threaded base of the modified spark plug is thereby encapsulated by the gas port chamber. A specially formed hole and slot direct compressed gas and vapor into a specially formed chamber on the interior of the gas port chamber. The compressed gas and vapor is directed from this chamber to a vent tube having a valve on the other end which prevents the gas from escaping into the atmosphere. By depressing a plunger located on the top of the valve, a motorcycle operator can vent a small portion of compressed gas and vapor to the atmosphere. This is done when starting the engine to reduce the pressure in the combustion chamber prior to combustion. When combustion occurs, the resulting increase in pressure closes the valve until depressed again by the operator at startup. 
     The foregoing description is included to illustrate the operation of the preferred embodiment and is not meant to limit the scope of the invention. The scope of the invention is to be limited only by the following claims.

Technology Classification (CPC): 5