Abstract:
Tooling and process for installing a split type, circular snap ring into a slotted or grooved wrist pin journal of a piston utilizing an installation sleeve member with an internal bore therethrough which is positioned against the piston so that its bore is aligned with the piston&#39;s wrist pin journal. The bore in the installation sleeve including a tapered passage to progressively radially inwardly constrict the snap ring as it moves axially through the installation sleeve. An elongated plunger assembly is moved axially to engage the snap ring and move it through the bore of the installation sleeve. The plunger assembly is sized to permit it to move through the entire extent of the tapered portion and into the piston&#39;s journal so that in turn the snap ring is moved into the wrist pin journal and finally into alignment with a retainer slot or groove into which the snap ring can radially expand outwardly into a seated position.

Description:
TECHNICAL FIELD 
     This invention relates to a tool for installing a snap ring retainer into operative assembly position in a piston and more particularly to new and improved tooling for seating a snap ring retainer into an annular slot formed in a wrist pin receiving bore of a piston to maintain the wrist pin in a central position such that the ends of the wrist pin are maintained in a desired spaced relationship away from the engine&#39;s cylinder wall. This invention further relates to a new and improved method of installing a snap ring retainer into an annular slot formed in the wrist pin receiving bore of the pistons. 
     BACKGROUND OF THE INVENTION 
     In internal combustion engines, a fall floating wrist pin are used to pivotally attach an end of a connecting rod to a piston for the purpose of accommodating reciprocating stroking movement of a piston in an associated cylinder of an internal combustion engine. Such a wrist pin support advantageously provides two stages or levels of wrist pin freedom during piston operation tending to reduce pin and bearing friction and wear. When properly installed in a piston and connecting rod assembly, a free floating wrist pin has the capability of relative rotation with respect to the connecting rod and with respect to a bearing or bore formed in the piston. This wrist pin bore in the piston consists of a pair of aligned bores extending through spaced apart boss-like portions of the piston. 
     During engine operation, the wrist pin is typically subjected to thrust loads in the lateral direction or axially of the wrist pin. This usually is caused by sideways moments of the associated connecting rod during piston stroking in the associated engine cylinder. If the wrist pin is allowed to be displaced a distance where an end of the pin physically contacts and rubs against the cylinder wall during engine operation, the cylinder wall and the piston may be damaged which might necessitate expensive repairs. To prevent such an occurrence, each piston utilizes snap ring retainers or wire end locks made of spring steel located at each end of the wrist pin. Specifically, the snap ring retainer is operatively mounted in an annular blind retainer slot or groove formed in the piston&#39;s wrist pin bore positioned at the outboard end of the wrist pin. A snap ring retainers at each end of the wrist pin maintains the wrist pin in centered position with each end portion spaced away the respective cylinder wall thus eliminating any potential damage to the cylinder wall and the piston. 
     Previously, punches and other similar hand tools have been used to force the snap ring into a radially constricted configuration and into the end portion of the pin bore for subsequent radial expansion into its annular blind retainer slot. Specifically, a tubular guide sleeve has been used to feed or move a snap ring retainer into and along wrist pin bores. However, use of this tubular guide sleeve has proven difficult especially for initially aligning the retainer and maintaining alignment once in the wrist pin bore. Even those having a high level of mechanical skill experience pop-out of a snap ring retainer from the guide sleeve at either the inboard or outboard end of the wrist pin bore rather than desired seating in the associated annular blind retainer slot. Thus, difficulties are often encountered by use of such tools in the installation of resilient snap ring retainers partly due to the problem of sensing exactly when the snap ring retainer is aligned with the annular blind retainer slot. Use of such tools frequently overcompresses the snap ring retainers in an inward radial direction which results in a weakened outward radial retention force necessary for the snap ring retainer to maintain its retention in the annular blind retainer slot. Use of these tools also imposes significant side loads on the snap ring retainers sufficient to distort and overstress the snap ring retainer and the damage is often sufficient to prevent a proper seating of the snap ring retainer in the annular blind retainer slot. Resultantly, this damage sometimes results in a disengaging movement or “popping-out” of the snap ring retainer from it&#39;s annular blind retainer slot which may possibly permit undesirable contact of an end of the wrist pin with the cylinder wall. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a new and improved installation tool for seating a snap ring type retainer into an associated annular blind retainer slot formed in a piston&#39;s wrist pin bore so as to properly maintain the wrist pin in a centered relationship with the piston. The tool further ensures that the snap ring retainer is not subjected to any substantial deformation which might damage the snap ring retainer and cause it to subsequently pop-out of its annular blind retainer slot. Typically, each piston utilizes two snap ring retainers, each seated in its own annular blind retainer slot formed in the piston&#39;s wrist pin receiving bores. One of the snap ring retainers is located at each of the opposite ends of the wrist pin for controlling axial movements of the wrist pin. Difficulties occur both in initially constricting the snap ring retainers in a radial direction and in then inserting and moving the snap ring retainer along the wrist pin bore. In addition, it is difficult to sense when the snap ring retainer has been axially displaced into a desired position where the snap ring retainer is free to radially expand or snap outward into the annular blind retainer slot which slots are hidden during installation of the snap rings. 
     By use of the subject installation tool, the snap ring retainer is gradually constricted radially to a predetermined diameter insufficient to result in over-compression as it is moved progressively into and along the piston&#39;s wrist pin bore. This simplifies the overall installation of the snap ring retainer from its initial loading into a guide and installation sleeve portion to its final insertion where the snap ring retainer expands into it&#39;s annular blind retainer slot. Further, the use of this tool is very straight forward so that it is readily used by persons even with minimal mechanical skills. Further, the subject tool fully contains and confines the snap ring retainers during installation thus minimizing any opportunity for the snap ring retainer to pop out or be damaged from over stressing. 
     Another object of this invention is to initially position and support the snap ring retainer in a guide and installation portion of the tool which has a fixed diameter bore adapted to receive the snap ring retainer and further having another portion with a tapered or funnel-like configuration to move the snap ring retainer and simultaneously radially constrict the snap ring retainer. This structure maintains the snap ring retainer in a natural transverse orientation and evenly loads it during displacement toward the annular blind retainer slot and also importantly minimizes the extent of the snap ring retainer&#39;s radial constriction. Accordingly, the radial compression or constriction of the snap ring retainer is carried out by the progressively tapered inner bore of the installation sleeve which has a minimum internal diameter corresponding to only a just sufficient minimum diameter equal to the diameter of the piston&#39;s wrist pin bore so as to prevent overcompression of the snap ring retainer and thus any chance of damage. 
     Another object of this invention is to simplify installation of wrist pin snap ring retainers and minimize loss or damage of such snap ring retainer during installation. The tool includes an installation sleeve with a tapered bore having a minimum internal diameter equal to the piston&#39;s wrist pin bore diameter for preventing over constriction or compression of the snap ring retainer. Cooperating with the installation sleeve is a specialized plunger assembly having a forward pin setting portion for piloting the snap ring retainer into the internal diameter of the piston&#39;s wrist pin bores. The plunger assembly includes an intermediate and solid cylindrical body section formed with an inboard end that fits into the inner diameter of the pin bore and serves to displace the snap ring in the installation sleeve and then from the installation sleeve into the pin bore and then smoothly into its retainer groove. The thin wall cylindrical sleeve is mounted on the intermediate cylindrical body section for initially moving the snap ring from its original position in the guide sleeve to a constricted position in which the cylindrical body can further be displaced relative to the guide sleeve and cylindrical sleeve to fully and properly seat the snap ring in its retainer groove. 
     These and other features, objects and advantages of this invention will become more apparent from the following detailed description and the drawings on some preferred embodiments of the invention: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a perspective view of a piston and connecting rod assembly with a wrist pin in a pre-installed position; and 
     FIG. 2 is an enlarged view of the piston and connecting rod assembly shown in FIG. 1 illustrating one part of the tooling assembly according to this invention utilized to install a snap ring retainer the wrist pin bore of the piston; and 
     FIG. 3 is a perspective view of the part of the tooling shown in FIG. 2; and 
     FIG. 4 is a perspective view of the remainder of the tooling assembly according to this invention set up to install a snap ring retainer to the piston; and 
     FIG. 5 is a cross sectioned elevational view of the tooling shown in FIG. 4 illustrating the beginning of installation operation of a snap ring retainer to a piston; and 
     FIG. 6 is a cross sectioned elevational view of the tooling shown in FIG. 5 illustrating an intermediate step in the installation operation of a snap ring retainer to a piston and showing a control radial constricting of the snap ring retainer; and 
     FIG. 7 is an enlarged and somewhat diagrammatic elevational view showing progressive movement of and radial inward constriction of the snap ring retainer as it is installed into a final position engaging an annular blind retaining slot of the piston; and 
     FIGS. 8 a ,  8   b ,  8   c  are sectioned and somewhat diagrammatic elevational views illustrating the installation operation of the subject tool. 
    
    
     DETAILED DESCRIPTION 
     Turning now in detail to the drawings, a piston and connecting rod assembly  10  for an internal combustion engine is illustrated in FIG.  1 . The assembly  10  comprises a cylindrical piston  12  which is adapted to be pivotally connected to an upper end portion of an elongated connecting rod  14  by a tubular wrist pin member  18 . The piston  12  has an annular skirt portion  20  in which a pair of laterally spaced side boss portions  22  are provided. Each side boss  22  has a cylindrical bore  24  therein which bores are coaxially aligned so as to permit insertion of the wrist pin  18  therethrough. The diameter of the wrist pin  18  is sized to permit rotation in the bores  24  during operation of the associated engine accompanied by reciprocation of the piston  12  in an associated cylinder bore. Referring to FIG. 5, the upper end portion  28  of the connecting rod  14  has a cylindrical bearing surface  26  formed by a bore which extends transversely and through which the wrist pin  18  extends. The diameter of the bore in end portion  28  relative to the diameter of the wrist pin  18  allows relative rotation therebetween during operation of the associated engine and accompanied by reciprocation of the piston  12  in an associated cylinder bore. 
     As probably most clearly shown in FIG. 7, the wrist pin  18  is maintained within the bores  24  in a substantially central location in the piston  12  as defined by a desired lateral spacing between the surface  22 ′ of the side boss  22  and the end  18 ′ of the wrist pin  18 . This position of the wrist pin  18  is maintained by a pair of snap ring retainers  32  (one shown in FIG. 7) which prevent any substantial axial movement of the wrist pin  18 . The retainers  32  are of spring steel and designed to be capable of being radially constricted and spring-back radially outwardly from the constricted condition. When a snap ring retainer  32  is seated in respective annular blind retainer slots or grooves  34  formed in a bore  24  as seen in FIG. 7, the wrist pin&#39;s end  18 ′ is restrained from axial or lateral movement. In this seated position, the inner diameter portion of the snap ring retainer projects radially inward into the bore  24  to block movement of the wrist pin. Thus, the wrist pin  18  is captured between the two snap ring retainers at either side of the piston and thus it cannot be displaced in the axial direction to a more outward positions past the side surface  22 ′ of the piston skirt  20 . If the wrist pin were to be allowed to move outwardly, it could contact the cylinder bore and physically abrade and otherwise damage the cylinder wall and even eventually damage the piston and its piston rings. 
     As previously pointed out, there are difficulties in first constricting and then installing a snap ring type retainer into a bore and thus seat it in an annular blind retainer slot or groove. These difficulties have been addressed and solved by this inventive tool and process. 
     The initial basic component of the installation tool is a cylindrically shaped snap ring guide and installation sleeve  38  as best seen in FIGS. 2 and 3. The sleeve&#39;s inboard end portion  39  is configured to mate with the outer face or surface  22 ′ of the piston&#39;s side boss portion  22 . The outwardly directed end portion  41  of the sleeve member  38  includes ring guiding bore  40  which extends through sleeve  38  and functions to guide the snap ring retainer into the piston&#39;s bore  24 . As best shown in FIG. 7, the bore  40  has a “lead-in” cylindrical portion  42  with a constant diameter designed to initially receive an annular snap ring retainer  32 . In the preferred embodiment, the diameter of the lead-in portion  42  is sized to very slightly radially constrict the snap ring retainer  32  for ease in “loading” and retaining the snap ring within the sleeve portion  38 . With this construction, the snap ring retainer  32  can be readily inserted into the lead-in and is maintained therein in a substantially “squared” starting position. Subsequently, the retainer  32  is moved axially through the sleeve  38  accompanied by inward radial constriction toward the center axis  44  of bore  42 . This radial constriction is accomplished by axial movement along a tapered guide bore portion  46  extending from the fixed diameter or lead-in portion  42  to the sleeve&#39;s end surface  39  which is in abutting relation to the piston&#39;s surface  22 ′. The diameter of the tapered bore portion  46  progressively decreases in a manner to inwardly radially constrict the snap ring retainer until its diameter eventually matches the diameter of the piston&#39;s bore  24 . The gradual transition provided by the guide and installation sleeve  38  facilitates a non-stressful movement of the snap ring retainer  32  into the bore  24 . 
     Alignment of the inward end portion of the tapered bore  46  and the piston&#39;s bore  24  is established and maintained by an elongated plunger assembly  50  which has a pilot stem portion  52  adapted to be inserted into the inner diameter center of the tubular wrist pin  18 . This aligns the tool&#39;s longitudinal axis with the axis of the wrist pin  18  and the bore  24 . 
     In addition to the pilot stem portion  52 , the plunger assembly  50  includes a cylindrically shaped snap ring displacement body portion  54 . The diameter of the displacement body portion  54  is only slightly smaller then the diameter of the piston&#39;s bore  24 . Accordingly, when the displacement body portion  54  is moved axially toward the right as see in FIG. 7, it progresses the snap ring retainer  32  along the tapered portion  46  and into the piston&#39;s bore  24 . Eventually, the snap ring retainer  32  is seated in an annular blind slot or groove  34 . Specifically, the forward or rightward end of the displacement body portion  54  carries a flat end ring portion  56  which allows it to engage the snap ring retainer once it has been radially constricted by beginning movement through the tapered bore portion  46  of the installation and guide sleeve  38 . 
     The plunger assembly  50  further includes a connector stem  58  which projects axially from the displacement body portion  54  to an exteriorly positioned handle portion  60 . The handle portion  60  preferably is configured as an enlarged diameter knob  64  readily engaged by an installer of the snap ring retainer. The knob  64  is secured to the end of the stem portion  58  by a threaded fastener  66  as seen in FIG.  4 . The diameter of the knob  64  is sized to conformably fit the palm of the installer&#39;s hand and is sufficient to spread the manually applied load evenly over the snap ring retainer  32 . 
     The plunger assembly  50  is provided with a tubular snap ring support sleeve member  68  which has a rightward opened end portion and a leftward closed end portion. The closed end portion has an aperture  59  to receive stem portion  58  therethrough. This construction permits axial movement of the handle, stem and displacement portions  64 ,  58 ,  54  relative to the support sleeve member  68 . As the displacement portion  54  is moved to the right, the snap ring retainer  32  is moved through the bore  40  of the tubular sleeve member  38 . 
     As best shown in the sequence found in FIGS. 5 through 7, the edge of sleeve member  68  defines an annular contact  70  having a diameter corresponding to diameter of the snap ring retainer when only slightly constricted as initially installed in the lead-in portion  42  of installation sleeve  38 . Specifically, FIG. 5 shows the alignment of the annular contact surface  70  with the snap ring retainer  32  at the start of the installation. Axial movement of the plunger assembly  50  produces rightward movement of the snap ring retainer  32  along and through the tapered bore  46 . 
     The sequence of the preferred method of installing a snap ring retainer is shown in FIGS. 8 a ,  8   b  and  8   c .The snap ring retainer  32  is manually or otherwise positioned or loaded into the lead-in portion or bore  42  of the installation sleeve member  38 . The sleeve member  38  is manually pressed against the outer face  22 ′ of the piston&#39;s side boss. FIG. 8 a  illustrates a start installation position with the displacement body portion  54  of the plunger assembly  50  telescoped within the thin walled installation sleeve member  68 . The guide and alignment stem portion  52  extends into the inner diameter of wrist pin  18  to align the plunger assembly with the bore  24  and wrist pin  18 . The thin wall sleeve member  68  and the plunger assembly  50  are moved manually to the left from the position in FIG. 8 a  to the position of FIG. 8 b  in which the sleeve member  68  can not move further to the left because of contact with the wall of tapered bore  46 . During this slight movement, the sleeve member&#39;s end  70  has axially displaced the snap ring retainer accompanied by the beginning of radially inward constriction of the snap ring retainer  32 . With the end  70  of the sleeve  68  engaging the beginning of the tapered bore, leftward movement of the handle  64  of plunger assembly  50  is possible. This leftward movement from the position in FIG. 8 b  to the position of FIG. 8 c  involves sufficient radially inward constriction of the snap ring retainer  32  so that its reduced outer diameter allows it to enter the bore  24 . The plunger assembly  50  is further advanced until the snap ring retainer  32  attains an axial position in bore  24  so that it is aligned with the annular blind retainer slot or groove  34 . At this position, the snap ring retainer  32  expands radially outwardly into the slot or groove  34 . This expansion and subsequent contact of the snap ring retainer  32  in the groove  34  produces a noticeable noise which advises the installer that the snap ring retainer has been successfully seated. The tool is then easily removed. 
     Once a snap ring retainer has been installed on one side of a piston, the tool is used in the same manner to install a snap ring retainer in the bore on the other side of the piston. This captures the wrist pin therebetween in a central or centered position. 
     While a preferred embodiment of the invention has been shown and described, other embodiments will now become apparent to those skilled in the art. Accordingly, this invention is not to be limited to that which is shown and described but by the following claims.