The most common method of attaching a piston to a connecting rod in Powersports applications is with a full-floating wrist pin. Full-floating pins pivot freely within both the little end of the connecting rod and the piston pin bosses. The wrist pin is held in check and kept from scratching the cylinder by a spring-loaded lock on each side that secures the pin between the pin bosses.
Wrist pin locks are spring-type fasteners designed to provide an interference fit in a groove machined at the edge of each pin boss on the underside of the piston. The locks keep the wrist pin centered within the pin bosses while allowing for rotation. The elasticity of the lock allows them to be deformed in some manner for installation and removal.
The most common lock used in Powersports applications is the wire lock. We asked ProX product manager about the use of wire locks in Powersports engines:.
The force of the chamfered piston pin against the wire is directed outward when contacting the clip, securing the clip in the retaining groove. The lightweight nature of the wire helps prevent any possibility of clip ejection at high RPM, which is something that is not possible with a snap ring type retainer.
Wire locks are also easy to install, sometimes with no tools at all using your fingers. Because of these benefits, wire locks are the most popular type of retainer used on the market. From small engines to Formula One, this is the preferred way to keep your piston secured. This lock can be installed with bare fingers or a mix of screwdrivers and picks, depending on the whims of the engine builder.
A modified version of the wire clip has upswept tangs on each end that have a similar function as the holes on a snap ring. There are three methods of attaching a piston to a connecting rod: Shown from left to right are three popular styles of wrist-pin locks: snap ring, wire clip and Spirolocks. Experienced engine builders have developed their own styles of installing each type of pin retention design.
For the circlip, one edge is started in the groove. Pin buttons are another means to secure the wrist pin. They install on either side of the wrist in bore interlocking with the oil rail. The Spirolocks has spawned legendary stories of agony, but many engine builders have developed quick and reliable methods of installing them. One of the best tips is to separate the coils slightly. Snap rings or Tru Arc retainers require special pliers for installation.
Just insert the tabs on the pliers into the holes on each end of the retainer, apply pressure to the pliers to compress the retainer, then install in the groove. The Lock-in tool is designed to install Spirolocks with minimal handling of the wire. The tool has different heads dedicated for specific wrist-pin sizes. The first step is wrapping the Spirolocks around the groove and positioning the end on the index mark. Once the leading edge is inside the groove, the tool is turned counterclockwise to install the lock on the first side of the piston.
Lock-in also has tool heads for dedicated sizes to help install circlips. The snap ring and Spirolocks must be used with wrist pins that have a flat face and the appropriate retaining groove in the piston pin boss. The circlip uses a wrist pin with a chamfered edge, right, and also must be used in the correct groove.
To assemble a full-floating piston and rod combo, first install one of the locks. Next, lube the connecting rod's bushing and insert the wrist pin. The final step is installing the lock on the opposite side.
Recent Posts. December February June March October July May April January November September August 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:. Turning now in detail to the drawings, a piston and connecting rod assembly 10 for an internal combustion engine is illustrated in FIG.
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 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. 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. This position of the wrist pin 18 is maintained by a pair of snap ring retainers 32 one shown in FIG. 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. 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. 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. 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's bore As best shown in FIG.
Subsequently, the retainer 32 is moved axially through the sleeve 38 accompanied by inward radial constriction toward the center axis 44 of bore 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's bore 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 Alignment of the inward end portion of the tapered bore 46 and the piston'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 This aligns the tool's longitudinal axis with the axis of the wrist pin 18 and the bore In addition to the pilot stem portion 52 , the plunger assembly 50 includes a cylindrically shaped snap ring displacement body portion The diameter of the displacement body portion 54 is only slightly smaller then the diameter of the piston's bore Accordingly, when the displacement body portion 54 is moved axially toward the right as see in FIG.
Eventually, the snap ring retainer 32 is seated in an annular blind slot or groove 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 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 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. The diameter of the knob 64 is sized to conformably fit the palm of the installer's hand and is sufficient to spread the manually applied load evenly over the snap ring retainer 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 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 As best shown in the sequence found in FIGS.
Specifically, FIG.
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