Patent Publication Number: US-8991354-B2

Title: Advanced angled-cylinder piston device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of provisional patent applications filed by the present inventor:
     Application No. 61/217,858, filed 2009 Jun. 6, Confirmation No. 5343   Application No. 61/271,522, filed 2009 Jul. 22, Confirmation No. 3572   Application No. 61/271,523, filed 2009 Jul. 22, Confirmation No. 3755   Application No. 61/273,363, filed 2009 Aug. 3, Confirmation No. 7705   Application No. 61/340,083, filed 2010 Mar. 12, Confirmation No. 3185   

    
    
     BACKGROUND 
     Field 
     This application relates to piston-plus-crankshaft devices. 
     BACKGROUND 
     Prior Art 
     The following is a tabulation of some prior art that presently appears relevant: 
     
       
         
           
               
            
               
                   
               
               
                 U.S. Patents 
               
            
           
           
               
               
               
               
            
               
                   
                 Pat. No. 
                 Issue Date 
                 Patentee 
               
               
                   
                   
               
               
                   
                 6,058,901 
                 May 9, 2000 
                 Lee 
               
               
                   
                 6,745,746 B1 
                 Jun. 8, 2004 
                 Ishii 
               
               
                   
                 4,664,077 
                 May 12, 1987 
                 Kamimaru 
               
               
                   
                 5,816,201 
                 Oct. 06, 1998 
                 Garvin 
               
               
                   
                 6,827,057 
                 Dec. 07, 2004 
                 Dawson 
               
               
                   
                 5,076,220 
                 Dec. 31, 1991 
                 Evans, et al 
               
               
                   
                 6,612,281 B1 
                 Oct. 2, 2003 
                 Martin 
               
               
                   
                 4,708,096 
                 Nov. 24, 1987 
                 Mroz 
               
               
                   
                 5,186,127 
                 Feb. 16, 1993 
                 Custico 
               
               
                   
                 5,544,627 
                 Aug. 13, 1996 
                 Terdev, et al. 
               
               
                   
                 4,702,151 
                 Oct. 27, 1987 
                 Munro, et al. 
               
               
                   
                 7,543,556 B2 
                 Jun. 9, 2009 
                 Hees, et al. 
               
               
                   
                   
               
            
           
         
       
     
     NONPATENT LITERATURE DOCUMENTS 
     
         
         Dr. Taj Elssir Hassan, “Theoretical Performance Comparison between Inline, Offset and Twin Crankshaft Internal Combustion Engines” (July 2008) 
         www.speedtalk.com/forum/Offset Bore &amp; Crank Centerlines 
       
    
     The angled-cylinder or offset-crankshaft technique of designing internal and external combustion piston engines, piston pumps, and gas compressors is a technology that has been met with limited success. Designers of such devices have little guidance when employing this design technique to achieve results that produce a piston device that yields maximum performance gains, while requiring a minimum amount of modifications to traditional or existing engine, pump, or compressor designs. 
     Previous efforts to test and document the performance gains offered by the angled-cylinder or offset-crankshaft technology have employed tests that were conducted on internal combustion engines. Prototypes were constructed, and cylinder pressures, thermo-dynamics, and other characteristics of these engines were taken while in operation—for example discussion www.eng-tips.com/forum/thread7-201777, www.speedtalk.com/forum/offset bore &amp; crank centerlines and U.S. Pat. No. 6,058,901 to Lee (2000). These tests mainly focused on some specific offset-crankshaft configuration targeted at some specific point in the combustion stroke. Additionally, new prototypes needed to be constructed to test configuration variables. This limited method of testing has produced misleading results. 
     Another method used to compare the performance between angled-cylinder or offset-crankshaft piston devices with conventionally configured piston devices focused on piston-to-sidewall frictions—for example “Reration between Crankshaft Offset and Piston Friction Loss. Amount of Offset and Engine Operating Condition”—Takiguchi Masaaki. Other efforts that have been employed are computer simulations and mathematical studies—for example www.camotruck.net/rollins/piston-offset, Theoretical Performance Comparison between Inline, Offset, and Twin Crankshaft Internal Combustion Engines—Taj Elssir Hasaan. These methods of determining performance gains have also produced misleading results. 
     The orientation of the cylinder in such devices is extremely critical to performance. Some of the prior art related to the angled-cylinder or offset-crankshaft suggest values that are ineffective—for example U.S. Pat. No. 6,745,746 B1 to Ishii (2004) and U.S. Pat. No. 4,664,077 to Kamimaru (1987). Others specify designs that are too impractical to be viable—for example U.S. Pat. No. 5,816,201 to Garvin (1998) and U.S. Pat. No. 6,827,057 to Dawson (2004). Still other prior art and patents are very indeterminate in defining this relationship. Such terms as “approximately” and “about” are typically used—for example U.S. Pat. No. 6,612,281 B1 to Martin (2003) and U.S. Pat. No. 5,076,220 to Evans et al (1991). Additionally, if values are expressed in prior art at all, they fail to take into consideration other critical factors such as connecting rod-to-stroke ratios, which would render any expressed value effectively meaningless—for example U.S. Pat. No. 4,708,096 to Mroz (1987). 
     Designers of piston devices wishing to employ the angled-cylinder or offset-crankshaft technology have also been confronted with mechanical interferences and clearance limitations between the cylinder, connecting rod, and piston. Prior art that has addressed this issue specify connecting rod designs that alter the connecting rod centerline, and therefore would be prone to early failure—for example U.S. Pat. No. 5,186,127 to Cuatico (1993) and US patent to Terzlev (1996). Manufacturers of piston devices would be reluctant to adopt such designs. Other prior art addressing this problem suggest integrating modifications to the block casting—for example U.S. Pat. No. 4,708,096 to Mroz. (1987). As the close proximity of the piston components with the bottom of the cylinder are critical in these devices, this approach would prove challenging in the manufacturing process. 
     Other concerns encountered when designing a piston device employing the angled-cylinder or offset-crankshaft technology have no known directly related prior art. 
     Advantages 
     Accordingly designs and methods for providing designers of angled-cylinder piston devices with the ability to produce a device that benefits from the mechanical advantage inherent in the technology, while requiring as few modifications to existing or traditional designs as possible, thus making the angled-cylinder or offset-crankshaft technology viable. 
    
    
     
       DETAILED DESCRIPTION-FIGS.  1 ,  2 ,  12 , and  13   
       First Embodiment  
         FIGS. 1 ,  2 ,  12 , and  13  share all the same components. A cylinder head  21  could contain valves, spark plugs or other components that are not necessary for this disclosure, and therefore are not included. The cylinder  22  can be a bore in a block casting, a sleeve inserted into a bore, or an independent structure. A piston  23  and a connecting rod  26  are pivotally joined at a piston pivot  24 . A piston pivot center axis  25 , and a piston pivot horizontal centerline  40  are included for reference purposes. A crankshaft main journal  33 , a throw  30 , and a crankpin  28  represent the moving components of a crankshaft, or crankshaft assembly, and positioned at top-dead-center (TDC). A crankshaft main axis of rotation  34 , and a crankpin center axis  29  are included for reference purposes. A stroke reference line  35  is included to show the travel of the crankpin center axis  29  as the crankshaft rotates 360° through an operating cycle. A length of connecting rod  27  and a length of throw  38  are included, as these dimensions are necessary for this disclosure. Both  FIGS. 1 ,  2 ,  12 , and  13  are drawings of what could be a single cylinder device, or one cylinder of a multiple cylinder device. 
         FIG. 1  is a drawing of an example of a piston designed using the angled-cylinder technique. A piston engine or motor employing this design technique basically begins with a traditional or existing design, and with the crankshaft  28 , 30 , 33  positioned to place the piston  23  at TDC (shown), a cylinder&#39;s centerline  37  orientation is rotated about the piston pivot center axis  25  location, thus orienting the cylinder&#39;s base in the direction of the crankpin  28  as the crankshaft&#39;s  28 , 30 , 33  operational rotation moves the crankpin  28  from TDC to bottom-dead-center (BDC). As illustrated in  FIG. 12 , in the case of a compressor or pump, the cylinder&#39;s centerline  37  orientation is rotated about the piston pivot center axis  25  location to orient the cylinder&#39;s  22  base in the direction of the crankpin  28  as the crankshaft&#39;s  28 , 30 , 33  operational rotation moves from BDC to TDC. 
         FIG. 2  is an example of a piston piston or motor designed using the offset-crankshaft or offset-cylinder technique. A piston engine or motor employing this design technique also begins with a traditional or an existing design, and the crankshaft&#39;s main axis of rotation  34  is offset in a perpendicular direction away from the cylinder&#39;s centerline  37 , toward the direction of the crankpin  28  as the crankshaft&#39;s  28 , 30 , 33  operational rotation moves the crankpin  28  from BDC to TDC. As illustrated in  FIG. 13 , in the case of a compressor or pump, the crankshaft&#39;s main axis of rotation  34  is offset in a perpendicular direction from the cylinder&#39;s centerline  37 , and toward the crankpin  28  as the crankshaft&#39;s  28 , 30 , 33  operational rotation moves the crankpin  28  from TDC to BDC. 
       If corrected for TDC, the angled-cylinder and the offset-crankshaft design techniques both produce a piston device with identical piston  23 , cylinder  22 , connecting rod  26 , and throw  30  component relationships. The difference between these two design techniques involves which components of a traditional or existing design will be altered to achieve the desired result. Therefore, going forward, this design technique will be referred to as the angled-cylinder design, as when considering only the basic components involved, it is a more generic description. 
       As previously disclosed, the angled-cylinder technique can be applied to engines, gas compressors and liquid pumps.  FIGS. 1 &amp; 2  illustrate the angled-cylinder technique applied to an engine or motor, either internal combustion such as a gasoline or diesel engine, or external combustion such as a steam engine. The throw  30 , and the crankpin  28  are represented in an alternate position of the operating cycle,  39  and  31  repectively. In the case of an engine, this position would be 90° past top-dead-center of a 360° clockwise crankshaft  28 , 30 , 33  rotation. As illustrated in  FIGS. 12 and 13 , in the case of a gas compressor or liquid pump, this position,  74  and  72  repectively, would be 270° past top-dead center of a 360° clockwise crankshaft  28 , 30 , 33  rotation. 
       DETAILED DESCRIPTION-FIGS.  1 ,  2 ,  3 ,  4 ,  12  and  13   
       First Embodiment  
         FIGS. 1 ,  2 ,  12  and  13  share all the same components. The unique technique I used to measure the torque and performance gains offered by the angled-cylinder piston device employed the use of a hobby-grade steam engine. The reasons for choosing this device were as follows: 
       1. Steam engines are typically built with open architecture lower ends. The crankshaft and connecting rod assemblies are not enclosed within a crankcase, and therefore they are exposed for easy experimentation. 
       2. The cylinder and piston assemblies of the steam engine used are constructed as individual components, and then mounted to a plate. The plate is then mounted to the lower assembly by means of machined posts. Adding a system of shims to these posts was a simple procedure, thus creating an assembly that could easily produce variable cylinder angles. 
       3. Steam engines are external combustion engines, and lend themselves to simple modifications that allow them to operate on controlled compressed air. This was critical, as my intention was to identify the performance gains offered by the angled-cylinder technique, without considerations of heat dissipation and accumulation, combustion gas expansion variations due to a multitude of factors, friction increases and decreases, and other variables related to combustion engines that could distort my observations. The modified steam engine allowed me to run tests that isolated the performance and torque gains inherent in the mechanical advantage of the angled-cylinder technique. 
       The test engine was assembled with the above mentioned modifications. The output shaft was fitted with a cogged-belt pulley that allowed coupling to an electric generator, also fitted with a cogged pulley, and joined with a cogged belt. The engine&#39;s pulley was also marked to allow engine revolutions-per-minute (RPM) readings to be made with an optical tachometer. Extensive tests were conducted, and the results were consistent.  FIG. 3  is a chart of typical test results produced when voltage readings were taken at various cylinder angles.  FIG. 4  is a chart of typical test results produced when RPM readings were taken at various cylinder angles. 
       Measuring the amount of modification in terms of cylinder angle became futile, as the small adjustments necessary became too difficult to gauge accurately when measured as cylinder angle. Therefore, I developed the more precise technique of measuring this configuration in terms of the intersection between the cylinder&#39;s centerline  37  with the length of throw&#39;s centerline  36 ,  38   FIGS. 1 ,  2 ,  12  and  13 . A traditional piston device would have its cylinder  22  oriented in a manner such that its centerline  37  would be drawn directly through the piston pivot center axis  25 , and the crankshaft main axis  34 . In the case of an engine or motor, using the throw  30  positioned at 90° of a clockwise crankshaft rotation  39 , and measuring from the crankshaft main center axis  34  to the crankpin center axis  32 , a cylinder oriented in such a manner as to have its centerline  37  intersect with throw&#39;s centerline  36  can have its orientation calibrated in terms of a percentage of the length of throw centerline  36 ,  38 . Going forward, this measurement will be referred to as cylinder centerline to length of throw centerline intersect  45 . This method of determining cylinder orientation can be effectively used when designing either an angled-cylinder, or an offset-crankshaft piston device. 
       What these tests allowed me to conclude are as follows: 
       1. The configuration of the cylinder centerline with the length of throw centerline intersect  45  is extremely critical. Very minute changes to the cylinder angle produces measurable changes in torque and performance. 
       2. The performance and torque gains that can be gleaned from the angled-cylinder technique are not linear. During testing, as the cylinder&#39;s centerlines  37  were oriented away from the crankshaft main axis  34  and towards the crankpin center axis position held at 90° of a clockwise rotation  32 , the gains were rather small until I approached a cylinder centerline to throw centerline intersect  45  of 30%. The gains then increased exponentially until reaching a throw centerline intersect  45  of 45%, and then began to decrease. Gains in performance rapidly decreased after reaching a cylinder centerline to throw centerline intersect  45  of 49%. It is within the range of a cylinder centerline to throw centerline intersect  45  of 30% to 49% that performance increases of 15% or more can be realized, and this range of cylinder  22  orientation is within the scope of the present embodiment. 
       DETAILED DESCRIPTION-FIGS.  1 ,  2 ,  5 ,  12  and  13   
       Second Embodiment 
         FIGS. 1 ,  2 ,  12 , and  13  share all the same components. Piston devices designed to operate with a cylinder centerline to throw centerline intersect  45  of 33% to 46% present certain challenges.  FIG. 5 , reference  48 , illustrates a limitation that would be presented when applying this technique to traditional or existing designs. The increased swing of the connecting rod  47  opposite the direction of cylinder angle or cylinder offset can cause an interference between the connecting rod  26  and the bottom of the piston  23 . This interference can also occur with the connecting rod  26 , and the bottom of the cylinder  22 . Another problem created by the exaggerated connecting rod swing  47  is the increase in friction between the piston  23  and the cylinder sidewall  22  as the piston travels from bottom dead center to top dead center in the case of an engine or motor, and from top dead center to bottom dead center in the case of a compressor or pump. A solution to these problems provided by this embodiment, is to balance the amount of cylinder centerline to throw centerline intersect  45  with the degree of interference and/or friction increases, which is in direct proportion to the devices connecting rod-to-stroke ratio. The amount of cylinder centerline to throw centerline intersect  45  is determined by assessing the connecting rod/stroke ratio, and selecting one of three classes: 
       CLASS 1—This class determines a specific cylinder centerline to length of throw intersect  45 . A piston device with a connecting rod/stroke ratio of less than 1.5/1 respectively presents a greater amount of interference and increased frictions, and therefore permits a lower amount of cylinder angle. Accordingly, a cylinder centerline to length of throw centerline intersect  45  of 33% is determined. In the case of a compressor or pump, a tolerance of +/- 3% of length of throw  38  is determined, and in the case of an engine or motor, a tolerance of +/- 2.5% of length of throw  38  is determined. 
       CLASS 2—This class also determines a specific cylinder centerline to length of throw intersect. A piston device with a connecting rod/stroke ratio of greater than 1.9/1 respectively presents a lesser amount of interference and friction increases, and therefore permits a greater amount of cylinder angle. Accordingly, a cylinder centerline to length of throw centerline in-tersect  45  of 46% is determined. In the case of a compressor or pump, a tolerance of +/- 3% of length of throw  38  is determined, and in the case of an engine or motor, a tolerance of +/- 2.5% of length of throw  38  is determined. Piston engines or motors with connecting rod/stroke ratios greater than 4/1 are outside the scope of this embodiment. 
       CLASS 3—This class determines a sliding amount of cylinder centerline to throw centerline intersect  45 . Piston devices with connecting rod/stroke ratios between 1.5/1 to 1.9/1 would have the cylinder centerline to length of throw centerline intersect  45  determined proportionally from 33% to 46% respectively, including the above stated tolerances. 
       The tolerances are to allow for other device characteristics such as connecting rod  26  width, or piston  23  diameter, and in the case of an engine or motor, expansion of components due to higher operating temperatures is considered. 
       This selection process provides the optimum amount of cylinder centerline to length of throw centerline intersect  45  as a function of the connecting rod/stroke ratio. 
       This method of determining optimum cylinder centerline  37  orientation is within the scope of the present embodiment. 
       DETAILED DESCRIPTION-FIGS.  5  and  6   
       Third Embodiment  
       Another concern when designing an angled-cylinder piston device is the interference between the connecting rod  26  and the piston&#39;s  23  base, also known as the piston skirt  75 , as shown in  FIG. 5 , reference  48 . The piston skirt  FIG. 6 , reference  75  is a functional structure normally required to keep the piston  23  parallel within the cylinder  22  as it transits past TDC and BDC of the crankshaft&#39;s  28 ,  30 ,  33 , 360° rotational cycle  35 . A solution to this issue provided by this embodiment is the recessed piston  46  as shown in  FIG. 6 . An area of relief  51  formed at the base or skirt of the piston  46 , and oriented in a manner to accommodate the swing of the connecting rod  26 , will provide clearance for the free operation of the connecting rod  26  throughout the crankshaft&#39;s  28 , 30 , 33  360° rotational cycle  35 . This method of overcoming mechanical interferences in the angled-cylinder piston device is within the scope of the present embodiment. 
       DETAILED DESCRIPTION-FIGS.  5 ,  6  and  7   
       Fourth Embodiment 
       Another concern when designing an angled-cylinder piston device is the interference between the connecting rod  26  and the cylinder&#39;s  22  base, as shown in  FIG. 5 , reference  48 . A solution to this issue provided by this embodiment is the recessed cylinder sleeve  53  as shown in  FIG. 7 . A sleeve inserted into a cylinder&#39;s bore  52 , and having an area of relief  55  that is oriented in a manner to accommodate the swing of the connecting rod  26 , will provide clearance for the free operation of the connecting rod  26  throughout the crankshaft&#39;s 360° rotational cycle  35 . This sleeve design is very effective, as piston devices designed using the angled-cylinder technique would require extremely accurate relationships between the piston rings  50 , and the area of relief  55  in the sleeve. Therefore, providing such an area of relief formed in a bored block would be challenging in the manufacturing process. A sleeve designed as described could be held in the cylinder&#39;s bore  52  either mechanically or through some bonding means, but would require some mechanical or bonding means to keep it from rotating within the cylinder bore  52 . A misalignment between the connecting rod  26  and the area of relief  55  would lead to failure. This method of overcoming mechanical interferences in the angled-cylinder piston device is within the scope of the present embodiment. 
       DETAILED DESCRIPTION-FIGS.  8 ,  9 , and  10   
       Fifth Embodiment 
       A designer of an angled-cylinder piston device wishing to avoid re-designing as many peripheral components as possible may take the approach of angling the cylinder  22  about the piston pivot  24  location at TDC in the original design. This design technique would avoid having to re-design the cylinder heads  21 , but would create a condition of excess cylinder volume  57  when the piston  23  is positioned at TDC, as shown in  FIG. 8 . A solution to this problem is to design a piston  59  whose top  60  is formed in such a manner as to compensate for this excess volume  57 , as shown in  FIGS. 9 and 10 . This solution may prevent the re-designing of many other internal and external components as well. This method of overcoming insufficient compression in the angled-cylinder piston device is within the scope of the present embodiment. 
       DETAILED DESCRIPTION-FIGS.  5  and  11   
       Sixth Embodiment 
       Another concern when designing an angled-cylinder piston device is the increase in friction between the piston  23  and the cylinder  22  wall as shown in  FIG. 5 , reference  49 . This increase in friction occurs as the piston  23  travels from BDC to TDC of the crankshaft 360° rotational cycle  35  in piston engines or motors, and from TDC to BDC in Piston compressors or pumps. If the piston device is centrally lubricated, a lubrication passage  67  formed in the connecting rod  26 , and oriented in such a manner as to tap the central lubrication supply and apply additional lubrication to the affected area  49  of the cylinder&#39;s  22  wall as shown in  FIG. 11 , would solve this issue. The movement of the connecting rod  26  as the crankpin  28  travels from BDC to TDC, or TDC to BDC would provide excellent lubrication distribution. A lubrication passage properly formed in the crankshaft  28 , 30 , 33  would provide the same benefit. This method of overcoming insufficient lubrication in the angled-cylinder piston device is within the scope of the present embodiment. 
       Thus the scope of the embodiments should be determined by the appended claims, and their legal equivalents, rather than by the examples given. 
     
    
    
     DRAWINGS 
     Figures 
       FIG. 1  shows a cross section of a cylinder, piston and crankshaft assembly which is an example of an angled-cylinder piston engine or motor configuration with the crankshaft positioned at top-dead-center. Also, an alternate position of the crankpin with the crankshaft positioned at 90° past top dead center of a clockwise rotation is shown. 
       FIG. 2  shows a cross section of a cylinder, piston and crankshaft assembly which is an example of an offset-crankshaft, or offset-cylinder engine or motor configuration with the crankshaft positioned at top dead center. Also, an alternate position of the crankpin with the crankshaft positioned at 90° past top dead center of a clockwise rotation is shown. 
       FIG. 6  shows an example of a recessed piston with an area of relief. 
       FIG. 7  shows an example of a recessed cylinder insert sleeve with an area of relief. 
       FIG. 8  shows an angled-cylinder piston device with the crankshaft positioned at top dead center. This figure shows the excess volume of the cylinder chamber at top dead center. 
       FIG. 9  shows an angled-cylinder piston device with the crankshaft positioned at top dead center. This figure shows the excess volume of the cylinder chamber at top dead center corrected with a compensating piston. 
       FIG. 10  shows an example of a compensating piston. 
       FIG. 11  shows an example of an angled-cylinder piston device with an additional lubrication passage. 
       FIG. 12  shows a cross section of a cylinder, piston and crankshaft assembly which is an example of an angled-cylinder piston pump or compressor configuration with the crankshaft positioned at top dead center. Also, an alternate position of the crankpin with the crankshaft positioned at 270° past top dead center of a clockwise rotation is shown. 
       FIG. 13  shows a cross section of a cylinder, piston and crankshaft assembly which is an example of an offset crankshaft, or offset cylinder piston pump or compressor configuration with the crankshaft positioned at top dead center. Also, an alternate position of the crankpin with the crankshaft positioned at 270° past top dead center of a clockwise rotation is shown. 
     DRAWINGS 
     Reference Numerals 
     
         
           21  cylinder head 
           22  cylinder 
           23  piston 
           24  piston pivot 
           25  piston pivot center axis 
           26  connecting rod 
           27  length of connecting rod 
           28  crankpin 
           37  centerline of cylinder 
           29  crankpin center axis 
           30  throw 
           31  crankpin position at 90° past top dead center of a clockwise crankshaft rotation 
           32  crankpin center axis position at 90° past top dead center of a clockwise crankshaft rotation 
           33  crankshaft main journal 
           34  crankshaft main axis 
           35  stroke path of crankpin center axis 
           36  throw centerline location at 90° past top dead center of a clockwise crankshaft rotation 
           37  centerline of cylinder 
           38  length of throw 
           39  throw position at 90° past top dead center of a clockwise crankshaft rotation 
           40  piston pivot horizontal centerline 
           41  connecting rod centerline 
           42  stroke diameter 
           43  crankpin horizontal centerline 
           44  crankshaft main axis vertical centerline 
           45  cylinder centerline with length of throw centerline intersect 
           46  recessed piston 
           47  connecting rod swing 
           48  point of interference 
           49  point of increased friction 
           50  piston rings 
           51  piston bottom area of relief 
           52  cylinder bore 
           53  recessed cylinder sleeve 
           54  location of cylinder bore bottom 
           55  cylinder sleeve area of relief 
           57  area of excess cylinder volume 
           59  compensating piston 
           60  compensating piston top 
           67  lubrication passage 
           68  indicates direction of rotational operation of crankshaft 
           72  crankpin position at 270° past top dead center of a clockwise crankshaft rotation 
           73  crankpin center axis position at 270° past top dead center of a clockwise crankshaft rotation 
           74  throw position at 270° past top dead center of a clockwise crankshaft rotation 
           75  piston shirt