Patent Publication Number: US-2019195165-A1

Title: Bolt-on cylinder kit and method for increasing the displacement of an engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/697,038, filed Sep. 6, 2017, now U.S. Pat. No. **, which is a continuation of U.S. patent application Ser. No. 14/674,222, filed Mar. 31, 2015, now U.S. Pat. No. 9,856,817, the entire contents of both of which are incorporated by reference herein. 
    
    
     BACKGROUND 
     The present invention relates to engine cylinders for a V-twin engine. 
     V-twin engines typically include, among other things, two cylinders arranged in a V-configuration. Each cylinder typically includes a body having an exterior surface that may optionally have fins (e.g., for an air-cooled engine). The cylinder also includes opposing ends, whereby a cylinder head is disposed on one of the opposing ends, while the other opposing end is received within the crankcase. A cylinder sleeve within the body defines a cylinder bore configured to slidably receive a piston coupled to a crankshaft of the engine via a connecting rod. 
     Many owners of V-twin engines, including motorcycle owners, look for ways to increase the power output available from their vehicle. Although some may replace the existing engine with an entirely different, larger engine, this can be extremely costly, labor intensive, problematic and time consuming. Thus, many find that upgrading the existing engine is a more viable option. One way in which power output is increased for an existing V-twin engine entails, among other things, upgrading the engine with a big-bore kit to increase displacement. An exemplary upgrade includes converting existing 96 in 3  and 103 in 3  Harley-Davidson Twin Cam engines to 110 in 3  displacement engines by providing replacement cylinders having cylinder bore diameters of 4 inches. 
     Along with the cylinder bore increase, the outer diameter portion of the sleeve that fits into the crankcase has a similar increase in size. This is because the cylinder sleeve wall thickness of the new cylinder is typically about the same as that of the original cylinder that is removed (i.e., typical wall thickness may be about 0.090 inch for cast iron sleeves) maintain the requisite sleeve strength. Thus, when replacing original cylinders with larger bore replacement cylinders as previously mentioned, it is also necessary to increase the diameter of the corresponding crankcase bores to which the cylinders are fitted. Increasing the size of the crankcase bores entails removing the crankcase from the vehicle, splitting apart the crankcase halves and machining the crankcase bores to allow fitting of the larger bore cylinders. Although not as involved as an entire engine replacement in some respects, this process is also very labor intensive and time consuming. 
     SUMMARY 
     The present invention provides, in one aspect, a cylinder for a V-twin engine. The cylinder includes a body with a first end having a surface configured to mate with a cylinder head, and a second end configured to mate with a crankcase. A sleeve is fixedly secured within the body to define a cylinder bore. The sleeve includes a first portion that extends from the first end of the body to the second end of the body. The first portion of the sleeve has a first wall thickness. The sleeve further includes a second portion that extends out of the second end of the body to be received within a crankcase bore. The second portion has a second wall thickness that is thinner than the first wall thickness. The sleeve is constructed from a chromoly steel alloy material, and the second wall thickness is less than 0.060 inch. 
     The present invention provides, in another aspect, a cylinder for a V-twin engine. The cylinder includes a body with a first end having a surface configured to mate with a cylinder head, and a second end configured to mate with a crankcase. A sleeve is fixedly secured within the body to define a cylinder bore. The sleeve includes a first portion that extends from the first end of the body to the second end of the body. The first portion of the sleeve has a first wall thickness. The sleeve further includes a second portion that extends out of the second end of the body to be received within a crankcase bore. The second portion has a second wall thickness that is thinner than the first wall thickness. The second portion has an outer diameter of about 4.068 inches, and the second wall thickness is less than 0.060 inch. 
     The present invention provides, in another aspect, a method of retrofitting a V-twin engine for increasing displacement. The V-twin engine is provided with a pair of cylinders, each of the pair of cylinders has a first cylinder bore diameter that provides the V-twin engine with a first displacement. Each of the pair of cylinders is dismounted from a crankcase of the V-twin engine. A pair of big-bore replacement cylinders is provided, each having a second cylinder bore diameter larger than the first cylinder bore diameter to provide the V-twin engine with a second displacement greater than the first displacement. A spigot portion of each of the pair of replacement cylinders is aligned with a respective bore of the crankcase. The spigot portion of each of the pair of replacement cylinders is inserted into the respective bore of the crankcase. The pair of replacement cylinders are secured to the crankcase without enlarging either bore of the crankcase. 
     Other features and aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a motorcycle according to one embodiment of the invention. 
         FIG. 2  is a cross-sectional view of a V-twin engine of the motorcycle of  FIG. 1 . The engine is in an original, conventional configuration. 
         FIG. 3  is a cross-sectional view of one cylinder of the engine of  FIG. 2 . 
         FIG. 4  is a bottom view of an engine cylinder according to one embodiment of the present invention. 
         FIG. 5  is a side view of the engine cylinder of  FIG. 4 . 
         FIG. 6  is a cross-sectional view of the engine cylinder taken along line  6 - 6  of  FIG. 5 . 
         FIG. 7  is a cross-sectional view of the V-twin engine of  FIG. 2  after being converted with a pair of the engine cylinders of  FIGS. 4-6 . 
     
    
    
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a motorcycle  50 . Although illustrated as a touring motorcycle  50 , aspects of the invention may be applicable to other types of motorcycles (i.e., standard, cruiser, sport bike, sport touring, dual-sport, etc.). The motorcycle  50  includes a frame  52 , a front wheel  54  coupled to the frame  52  through a steering assembly  56 , and a rear wheel  58  coupled to the frame  52  through a swing arm assembly  59 . The motorcycle  50  includes an engine  60  coupled to the frame  52  and operatively coupled to the rear wheel  58  through a transmission  62 . As described below, the engine  60  can be a factory original engine that is modified to increase displacement in accordance with the structures and methods disclosed herein. 
     Illustrated separate from the motorcycle  50  in  FIG. 2 , the engine  60  includes a pair of cylinders  100  ( FIG. 3 ) oriented in a V-configuration and coupled to a crankcase  64 . On one end, a bottom end, each cylinder  100  is positioned in a crankcase bore  66  extending through a crankcase outer surface  68  such that a crankshaft  72  positioned in the crankcase  64  can be coupled to a piston  76  within each of the engine cylinders  100  via a corresponding connecting rod  74 . On the other end, a top end, the cylinder  100  receives a cylinder head  70 . 
     Each of the cylinders  100 , as shown in  FIG. 3 , includes a body  104  and a cylinder liner  108 . During construction of the cylinder  100 , the body  104  is formed by a casting process around the liner  108 . Thus, the cylinder liner  108  is fixedly secured within the body  104 . The liner  108  defines a cylinder bore  112  and a spigot  116 . The spigot  116 , which extends out of the body  104 , is configured to be received by the crankcase bore  66 . The liner  108  and the spigot  116  share the same inner diameter D 1 . However, the liner  108  and the spigot  116  have different outer diameters, such that the spigot  116  has an outer diameter of D 2 , and the liner  108  has an outer diameter greater than the spigot outer diameter D 2  above the spigot  116 . The difference between the inner diameter D 1  and the outer diameter D 2  of the spigot  116  defines a wall thickness T 1  of the spigot  116 . The outer diameter D 2  of the spigot  116  is designed to have a clearance (e.g., 0.025 inch) between the crankcase bore  66  and the spigot  116  to ensure a slip fit between the components. 
     The cylinder liner  108  of the factory original cylinder  100  may be constructed of cast iron. In one such example of an existing Harley-Davidson Twin Cam engine, the cylinder liner  108  is cast iron and provided with a spigot wall thickness T 1  of 0.090 inch and an inner diameter D 1  of 3.875 inches. Although durable, the brittle nature of cast iron results in the inability to machine or re-sleeve the cylinder  100  as the spigot  116  will not have the appropriate design characteristics required to achieve a reliable and robust design if the outer diameter D 2  is limited to the size of the existing bore  66 . Due to the practical limitations of ordinary cylinder sleeving material, it is common that any big-bore replacement cylinders include a wall thickness equal to or greater than the original cylinder spigot wall thickness T 1 , which necessitates increasing the size of the crankcase bores  66 . In certain exemplary engines, such as Harley-Davidson Twin Cam engines, the crankcase bores  64  have a diameter of about 4.080 inches, which provides a diametric clearance, for example 0.025 inch, with the outer diameter D 2  of the spigot  116  of the factory original cylinders  100 . However, as previously mentioned, it is necessary to enlarge the crankcase bores  66  when retro-fitting the engine  60  with a big-bore kit. 
     Shown in  FIGS. 4-6  is a big-bore cylinder  200  that increases displacement of the engine  60  and that can easily be retrofitted to the crankcase  64  of the engine  60  originally provided with the cylinders  100  of  FIG. 3 . Switching to the cylinders  200  increases the displacement of the engine  60  in a simple bolt-on process that eliminates the current labor intensive process described above. In a particular exemplary construction, a pair of the big-bore cylinders  200  convert either one of an existing 96 in 3  Harley-Davidson Twin Cam engine having cylinder bore diameters of 3.750 inches and an existing 103 in 3  Harley-Davidson Twin Cam engine having cylinder bore diameters of 3.875 inches to have a displacement of 110 in 3  by increasing cylinder bore diameters to about 4.000 inches. As described below, the cylinders  200  are designed such that they fit into the existing bores  66  of the crankcase  64  such that the engine  60  can be converted to a larger displacement without having to remove, disassemble, or machine the crankcase  64 . 
     Each big-bore cylinder  200  includes a body  204  having a finned exterior  208  configured to increase efficiency of heat transfer of the air-cooled engine. As previously mentioned, the existence of the finned exterior  208  and the particular engine class (i.e., air-cooled) merely represent one exemplary embodiment. As such, it will be understood that, in other constructions, the cylinder  200  may be designed for a liquid-cooled engine and may or may not include a finned exterior. 
     Additionally, the body  204  includes a first end  212  with a surface  216  configured to mate with a cylinder head  70 ′ which can be a modified version of the cylinder head  70  of the original engine  60  of  FIG. 2 . The body  204  further includes a second end  220  with a flange  224  providing a surface configured to abut the crankcase  64 . The distance between the first end  212  and the second end  220  define a height H 2  of the cylinder  200  which, in this case, is the same as a height H 1  of the cylinder  100 . Furthermore, extending through the body  204  from the surface  216  are a plurality of mounting holes  228  (e.g., four symmetrically arranged mounting holes). Each of the mounting holes  228  is configured to receive a fastener (not shown) to removably couple the cylinder  200  to the crankcase  64 . 
     The cylinder  200  includes a sleeve  232  fixedly secured within the body  204  to define a cylinder bore  236 . The sleeve  232  may be fixedly secured by a casting process whereby the body  204  is formed onto the exterior of the sleeve  232 . The sleeve  232  has a main portion  240  and a second portion or spigot  244 . The main portion  240  extends from the first end  212  to the second end  220  within the body  204 , and the spigot  244  extends out of the body  204  and protrudes past the second end  220 . When the cylinder  200  and the crankcase  64  are coupled, the crankcase bore  66  receives the spigot  244 , as shown in  FIG. 7 . 
     In some constructions, the sleeve  232  is manufactured from tubing. The tubing can be cut to length, and machined in a subtractive process to form the spigot  244 . As depicted in  FIG. 6 , the main portion  240  has a wall thickness T 2 , and the spigot  244  has a spigot wall thickness T 3  different from the wall thickness T 2  of the main portion  240 . In the illustrated construction, the spigot wall thickness T 3  is thinner than the wall thickness T 2  of the main portion  240 . In order to provide a large bore size with a limited outside dimension, the spigot wall thickness T 3  may be less than 0.060 inch. The spigot wall thickness T 3  may be greater than 0.025 inch, and in some constructions, greater than 0.030 inch. In some constructions, the spigot wall thickness T 3  is less than 0.050 inch, and furthermore, the spigot wall thickness T 3  may be less than 0.040 inch. In some embodiments, the wall thickness T 3  is about 0.034 inch (e.g., 0.033 inch to 0.035 inch). In a construction where the outer diameter D 1  of the spigot portion  244  is about 4.068 inches (e.g., 4.067 inches to 4.069 inches), the thin wall thickness T 3  allows a cylinder bore diameter D 3  that is greater than 3.948 inches. In some constructions, the bore diameter D 3  is about 4.000 inches (e.g., 3.9997 inches to 4.0005 inches). Whether the outer diameter D 2  of the spigot portion  244  is at, above, or below 4.068 inches, diametric clearance may be provided between the spigot portion  244  and the crankcase bores  66  to enable a slip fit of the spigot portion  244  into the crankcase bore  66 . For example, the nominal diametric clearance is 0.012 inch when the outer diameter D 2  of the spigot portion  244  is 4.068 inches and each of the crankcase bores  66  has a diameter of 4.080 inches. 
     The sleeve  232  is constructed from a material that is substantially less brittle than cast iron. For example, the sleeve  232  can be constructed of a type of chromoly steel alloy material. In some constructions, the sleeve  232  is constructed from SAE grade 4140 steel. 
     Additionally, the radially exterior surface of the main portion  240  of the sleeve  232  includes an intersecting helical pattern having a helical coarse rib  248  and a helical fine rib  252 , each protruded radially outward as shown in  FIG. 6 . The helical ribs  248 ,  252  may be provided in the form of two different sized screw threads. The axial component of the helix is opposite for the two helical ribs  248 ,  252  such that one of the helical ribs  248 ,  252  is provided in a right hand rotation direction (i.e., clockwise), and the other of the helical ribs  248 ,  252  is provided in a left hand rotation direction (i.e., counterclockwise), which provides the intersecting pattern. Each of the helical ribs  248 ,  252  extends a majority of the height H 2  of the main portion  240 . The intersecting helical pattern is designed to securely lock the body  204  and the sleeve  232  together against separation or movement, particularly from rotational forces caused by twisting or vibration. 
     The design of the cylinder  200  enables it to be used in place of one of the factory original cylinder  100  to increase the displacement of the engine  60  without removal of the crankcase  64  and modification to the crankcase bores  66 . The process entails a simple removal procedure of the cylinders  100  and replacement procedure with the corresponding big-bore cylinders  200 .  FIG. 7  illustrates an engine  60 ′ that results from converting the engine  60  of  FIG. 2  with the installation of the cylinders  200  after removal of the cylinders  100 . During installation, the spigot portion  244  of each cylinder  200  is aligned with and inserted into the respective crankcase bore  66 , which is unmodified and retains its original size which was provided when accommodating the original, smaller-bore cylinder  100 . The installation of the cylinders  200  may be performed as part of a kit of corresponding parts matched with the cylinders  200 . For example, converting the engine  60  to the modified engine  60 ′ may include installation of new pistons  76 ′ (and corresponding piston rings) in addition to the cylinder heads  70 ′. New connecting rods  74 ′ may optionally be provided and installed as well, although alternately, the factory original connecting rods  74  may be re-utilized when upsizing the displacement. The engine cylinder  200  may be removably secured to the crankcase  64  with suitable fasteners. Also provided is the cylinder head  70 ′ for each cylinder  200 . 
     The embodiment described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention.