Wiseco wrist pin

Wiseco wrist pin DEFAULT

Wrist pin offset is a useful tool used by OEM and aftermarket piston engineers alike. Here's an explanation of the process and why it's done. 

On the surface it seems quite logical that the piston pin bore would be centered in the cylinder bore of any internal combustion engine. Having the cylinder axis intersect the crank axis is a time-honored tradition among engine designers. It has been the normal practice in production engines for well over a century, but time has a way of adjusting our thinking to newer and better ways.

As engines evolved, engineers determined that offsetting the piston (wrist) pin yields two major benefits. First, it improves the noise characteristics of the engine due to piston slap at top dead center (TDC). This is a major NVH (noise vibration and harshness) concern to production engineers who want to eliminate alarming noises anywhere they can. The second reason is to improve engine output by reducing internal friction.

Offsetting the cylinder axis from the crankshaft axis, minimizes rod angularity when cylinder pressure is at its highest. Reduced angularity leads to lower piston thrust forces, hence lower frictional losses during the period of maximum cylinder pressure, especially at the beginning of the power stroke when pressure rises sharply about degrees after TDC. Rather than revising a complete engine design, the easy way to do this is to offset the pin bore in the piston. This allows the same crank/rod pin axis geometry as an engine designed with offset cylinder axes, but within existing conventional engine architecture.

 

The amount by which the cylinder axes need to be offset depends on many variables, but the main ones are the ratio of crank throw to con rod length and the angle after TDC at which maximum cylinder pressure occurs. Moving the pin bore is more practical Wiseco Pistons have determined that a pin bore offset of inch is enough for most applications. They are also aware of the effect on engine stroke length due to offsetting the pin bore. Offsetting the pin bore slightly increases the stroke which may be enough to throw the engine out of spec for some racing classes that limit displacement visa bore or stroke.

Moving the pin bore enjoys a similar benefit to adding rod length in that it slows the piston speed at TDC thus allowing a longer period for flame propagation to build cylinder pressure before the power stroke really gets under way. The tradeoff is higher velocity approaching TDC and lower velocity departing TDC which may affect fuel octane requirements. While not as beneficial on short track applications, it does offer an advantage on longer tracks or in drag racing and Bonneville applications. The improved leverage angle while maintaining TDC is still important. Delaying pressure while the crank moves to a better leverage angle will help increase torque particularly at low rpm.  It should be noted that the effects are minimal but nonetheless found to be beneficial when they are applied in max effort applications.

A lot of mathematical calculation goes into the slider/crank relationship regarding pin bore offset, but Wiseco engineers have calculated the optimum amount of offset for performance applications and apply it where required. Special fixtures are used to accurately offset the pin bores. For pins that also intersect the oil rig groove, offset pins do not compromise oil ring function since the oil rings use a support rail for stability. The effects on rod loading are minimal as most modern connecting rods easily handle the loads. In supercharged cases, strong rods are typically included in the build as a matter of course.

Sours: http://blog.wiseco.com/what-is-wrist-pin-offset

Most have heard of spirolocks and other methods of wrist-pin retention, but when it comes to all-out racing, wrist pin buttons reign king of strength and simplicity. 
When the application calls for a sturdy, full-round piston in a high-performance engine, wrist-pin buttons have long been an option for keeping the piston secured to the connecting rod. In some piston designs where the wrist-pin bore invades the oil-ring groove, these buttons can actually force a kink to the oil rings under extreme stress. But a new, patented wrist-pin button from Wiseco is helping to eliminate the impacts that destroy those rings and, therefore, extend the engine’s lifecycle.

“We’ve been using it on Pro Mods and Radials vs. The World cars for two, three years now,” says Wiseco technical sales associate Vic Ellinger. “Everyone who has them has alleviated a lot of issues that they had before with conventional buttons.”

Engine builders who service today’s high-horsepower racing engines on a regular schedule have always been grateful for wrist-pin buttons and the time they save in the shop or pits. Not only does the piston and ring assembly come apart and go together quicker, there’s also a lot less bloodshed by not having to remove and install four sharp-edged Spirolox retaining clips needed on every piston. Aside from the time factor, the pin can “plow” open the groove that supports the Sprirolox or cnap ring and increase the side clearance.

“Buttons maintain end play of the pin,” says Ellinger. “It lets the pin float freely and not bind against the clips. A design utilizing clips won’t float as easily if the stack-up tolerances of the pin, lock-ring spacing and clipsare on the tight side, and the parts are expanding rapidly during the course of a run. Asthe pin is hammering the buttons side to side, it’s not going to open up that side clearance more than a few thou during a season.”

There is a potential downside, however, to using pin buttons when the wrist-pin bore actually cuts into the oil-ring groove and interferes with a portion of the support surface that ring land provides. Unfortunately, this design option is needed on pistons with short compression heights where the engine builder is using the longest connecting rod possible. Or it’s used in high-boost or nitrous applications where the ring grooves are moved away from the heat in the piston crown, or the lower location is needed to increase the strength of the crown area.

The wrist-pin buttons designed for these applications are machined with a slot that matches the oil-ring groove of the pistons. The oil ring can be installed alone or with a support rail. These oil-ring support rails never come into contact with the cylinder wall and have no effect on lubrication. Their sole purpose is to stabilize the oil ring pack, and they are designed with dimples in strategic locations to keep them from rotating inside the ring groove. Problems, however, can arise when the wrist-pin buttons twist inside the pin bores and pinch the oil ring and its support rail.

“With nitrous, it shocks the button so hard, that it actually kinks the scraper and locks up the oil ring. It’s like you stuck them in a vice. Right where the button would hit the rail, it would have a big kink mark in it,” says Ellinger. “Just kicks it right up and it looks like you hit it with a chisel.”

Wiseco’s solution to prevent the buttons from twisting and damaging the oil ring is to machine a pair of dog-ear-shaped dowels—one on each side of the button. These dowels match up with a pair of receiver notches that are machined into the pin bore.

“When the button drops in, it can't move and rotate in the bore. Then you can also eliminate the oil rail support, which gives you an extra .030-inch worth of ring land to use wherever you need it, especially for boost or nitrous,” explains Ellinger. “That's basically the reason, it won't kink the scraper and you free up real estate on the ring lands."

The new buttons with the D-shaped ears are machined from 2618 or 4032 billet alloy to match the construction of the pistons. The corresponding receiver slots are plunged cut on a hand mill. The buttons are designed to allow lateral movement as needed for the clearances, but the design eliminates any rotation within the pin bore. The recommended clearance between the pin, buttons and cylinder wall is dependent on a variety of factors, including bore size, pin size and piston material.

“All that has to be taken into account. And we like to see, depending on the application, it could be as tight as .005-inch or as loose as .015-, even .020-inch,” says Ellinger. “It just depends on what the specs are of the motor, and the type of application. If it's Bonneville, that's going to need something different where they're chilling the engines to rather cold engine tempsand immediatelyputting them into extreme conditions. You have to take into account how fast the parts are going to grow.

“The bore size is going to determine what end play you have with the length of the button, so your stack-up tolerances are going to give you what your number is,” continues Ellinger. “But, obviously, the stack-up tolerances can cause some variance with the manufacturer of the pin, or what brand pin. Also, if you open up the bore to allow for more clearance for a high-horsepower application, that's something that needs to be known during the design phase. If you're plus-one, plus-two, three-thousandths over what the nominal bore size is, we've got to compensate for that with the pin bore.”

The clearance for the buttons and pins is calculated based on the final bore size, length of the pin and a target side clearance. For example, a 4.600-inch bore matched with a 2.930-inch-long pin and a desired .005-inch end play = X clearance. Wiseco engineers can then calculate the required length for each button.

“The dowels are free floating, probable .0007- to .001-inch clearance. Most guys just install the piston upside down without the rod and give it a wiggle test. An experienced hand can tell if something is awry,” adds Ellinger. “Some actually assemble the parts and measure the overall length of the pin and buttons and make sure it has at least .005 less than the bore size for a measured length.”

Obviously the use of a wrist pin button requires a full-round piston so that the bottom side of the button has a shelf upon which to rest. Some engine builders may be leery of the extra weight that comes with pin buttons, so Wiseco rifle-drills a hole through the pin axis of the button.

“And we lighten them up on the backside, if we can,” adds Ellinger. “But typically, with these applications, they're more like diesels as far as the strength that's needed. The weight isn't an issue, because the rod and the crank are usually also fit for use. So, the rods are beefier. The cranks are better quality billet. So all that just kind of depends on just the power level, but typically the weight isn't an issue with those type of builds as they are with a naturally aspirated deal.”

Ring choice may be a little more flexible with the use of the new Wiseco pin buttons, but there are limitations due to the engine size and use.

 “You really want to lean towardshigher-tension oil rings just because of the swept area of oil volume you have to try to control, especially with a setup like 5.000-inch pistons and 5.875-inch stroke,” explains Ellinger. “I mean, there's just so much oil up there sloshing aroundthat they really need to be able to keep that oil off those cylinder walls as much as possible, and have it controlled. Because they're only on the gas for four seconds, three seconds, and they're really hard to control all that oil while it's surging up the back cylinder walls.”

Although pin buttons are used most often on high-end, frequently serviced race engines, they’re also suitable for many other applications.

“No, you can use it in any application, really, motorcycle, car, boat. The highest horsepower stuff is usually where we put it but you could even use it in a bracket engine,” says Ellinger. “There are a lot of benefits to it because it's the closest thing you can get to a true, non-stroker style piston design for a stroker. We've even used them where we've gotten into the second ring groove. We had to machine a second ring groove and an oil groove into the button because we lowered the lands to increase the strength of the piston, like a Top Fuel part would be.

“Wrist-pin buttons are really simple,” sums up Ellinger. “There's nothing there other than getting the things to quit ruining really expensive ring packs. That's really what they've done is brought oil consumption under control and eliminated the need for an oil rail support to add .030-inch worth of ring land to where you need it most, up top.”

Sours: http://blog.wiseco.com/what-are-wrist-pin-buttons
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The toughest piston in the world is useless if the wrist pin gives up the ghost. Here is a breakdown of what the wrist pin does, why they fail, and when to upgrade them to improve the strength of your engine combination. It has been said that the piston and connecting rod are the most tortured parts in a performance engine. Few engine builders dispute that notion, but what about the less glamorous piece of steel that mates them together through thick and thin? In a sense, the wrist pin is like the unsung soldier who throws himself across the barbed wire barrier while the rest of the troops run across his back. Stroke for stroke, the wrist pin takes one for the team every bit as much as the rod or the piston. If you’re using high-level forced induction, nitrous oxide injection, high rpm or heavy sustained loading on your performance engine, upgraded wrist pins represent the insurance deal of the century.

The wrist pin is charged with the daunting task of snatching the piston back from the brink of disaster hundreds of times per second in the face of massive cylinder pressure and alternating loading that can approach g’s. Under these conditions, the pin can bend and distort into an egg shape even if it is well lubricated. The worst case occurs when the piston reverses direction at the top of the exhaust stroke. There is little or no cylinder pressure to cushion the reversal, so the pin bears the full weight of the high-speed piston as it is yanked back down the cylinder. On the intake stroke the piston reverses against rising cylinder pressure that typically peaks around twelve degrees after top dead center (TDC). Here, the inertia loading is also substantial, but it is cushioned by the force of the combustion event.

It would be difficult to overstate the importance of the wrist pin in any high-rpm or high-power environment. In some normally aspirated applications seeking maximum compression ratio, many builders push the piston to head clearance right up to the point of leaving very slight witness marks on the piston crowns. Hanging on to the piston at very high piston speeds and tight clearances becomes crucial to engine survival. In other cases, high cylinder pressures via nitrous or forced induction attempts to bend and deform the wrist pin. When the pin bends, it tries to force the lubricant out of the way and friction increases. More power is consumed, and the associated heat tries to destroy the pins, pistons, and connecting rods.

What’s the Best Wall Thickness?

Armed with this knowledge we must ask what factors influence pin choice and what power levels or applications call for increased wall thickness, better materials and/or special coatings? More power always equals more cylinder pressure, so we are obliged to consider parts that complement the engine’s power level. As a rule, most off-the-shelf performance pistons are supplied with appropriately sized pins for the intended application. Of course, racers often abuse that with the addition of power adders that can easily increasing pin loading beyond what standard pins can tolerate.

As with everything in racing and many high-performance street engines, pin choice is application specific. Your piston supplier won’t provide something that is not up to the job, but you must be honest with yourself about your intentions. In a racing environment, tool steel wrist pins with a inch wall thickness are often adequate for most normally aspirated applications, but big block engines exceeding horsepower, need pins with a minimum inch wall thickness because they are slinging around heavier pistons.  And if you are running high boost or nitrous oxide, the pins must be compatibly thicker and of top grade material. Wrist pin deflection, insufficient pin clearance or poor lubrication all combine to magnify the detrimental effects of an inadequate pin selection.

Here's a handy ballpark chart you can use for preliminary wrist pin selection before you talk to the techs about your exact requirements.

Normally aspirated
Stock pins        HP
         HP

* If you are street supercharging or using a mild NOS shot its good practice to step up a bit more from the recommended normally aspirated pin sizes

Supercharged or NOS
         HP (H13 and DLC recommended)
         HP (H13 and DLC recommended)
         HP-plus (M2 or TP1 and DLC recommended)

According to Steve Rhodey at Trend Performance, “The wall thickness is subject to change upon more info obtained at the time of tech. A lot of wall thicknesses will overlap and that’s ok. It’s all about getting the right part. A lot of people have it in their heads that pins only dictate rotational mass, but that’s not always the case considering the loading a wrist pin can see. There won’t be ANY mass to worry about if the pin is too light.”

Among other things to discuss with your tech rep, pin clearance and lubrication quality rank high. Any application powerful enough to flex the pin will benefit from loosening up the pin clearances. Most pins run with a clearance of inch. For severe usage and big cylinder pressure, you can avoid trouble by opening the pin clearance to inch. Tight clearances are often a disaster waiting to happen. Looser is almost always safer, particularly if there are also lubrication issues.

Typical wet sump systems offer plenty of oil splash to help lubricate the pins. In a racing application, you often have dry sump lubrication, a crank scraper, a pan kickout and a vacuum pump to dramatically reduce oil in the pan and available splash lubrication. Windage and the oil fog can be over-controlled in some cases. Some builders even report greater signs of pin distress on the side of the engine with the crank scraper and pan kickout because they are so effective at stripping away the oil on that side of the engine. Extra clearance always helps in this environment.

In almost every high-pressure environment, tool steel pins, DLC coatings, looser clearances and sufficient lubrication are the insurance you need. Trend Performance addresses these needs with a full range of pin selections to cover every possible environment.

Beginning with Trend’s G-Series, pins are produced from chrome molybdenum thick-wall solid stock, a popular choice with, piston manufacturers, and shelf-stock piston sellers due to better material and precision machining. alloys are superior to the common mild steel alternative. This steel pin is ideally suited for use in naturally aspirated race engines. Pins are heat treated (60 Rockwell O.D./45 core), tumbled, and ground to and wall selections.

Trend uses H13 tool steel for most of its premium piston pins. H13 is considered the best all around material for most applications, especially in power-adder engines; it is also a popular choice in Pro Stock drag racing engines. H13 pins have a Rockwell hardness value around Rc54 and easily accept a DLC (Diamond-Like Carbon) coating. These pins are offered for all popular applications in inch wall thickness increments from inch to inch and , , and inch walls for severe applications. H pins are also ID honed for stress relieving and hard turned ends and chamfers can be added if required.

TP1

A new Trend pin alloy, TP1 is exceptionally hard and very tough. It is coated and less expensive than its rival, C maraging steel and it is specified exclusively for Top Fuel, Funny Car, and Pro Stock engines. These new pins are currently available in custom sizes or stocking sizes of , and inch. This material is becoming very popular in the high horsepower sport compact world, pro mod, Radial, and sportsman arenas. Even a lot of limited late model, super late model, outlaw and sprint cars are running it for its ability to be put through hell and stay round.

Top Fuel and Funny Car teams typically run their pins until they bend, which is almost immediately. They don’t coat their pins because it adds expense to disposable components.

Trend believes its new coated TP-1 pin possesses far superior longevity and the ability to resist galling and extreme bending moments. It is heat treated to a through-hardness of Rc60 (hardened from it outer case to its inner core), This pin combines the toughness of the maraging steels and the hardness, compressive strength, and surface qualities of M2, the superior high-speed tool steel.

In terms of tensile strength and yield strength, H13 pins and the newer M2 and TP1 pins are well beyond more common and alloys, but they are applications specific. It’s vital that you talk with Trend’s experienced techs to help you “pinpoint” the pin you need for your engine. There is really no environment too tough for Trend Performance wrist pins, but you gain the greatest benefits by upgrading to the proper size and level of prep. A little bit thicker walls with looser clearances and good lubrication can ensure that all the combustion pressure you generate is used to turn the crank and not merely drive the piston down the rod when a pin fails. Don’t overlook this critical step in your build sheet selections.

Sours: http://blog.diamondracing.net/when-to-upgrade-wrist-pins
Do I need to Buy Upgraded Wrist Pins? Jay's Tech Tips #28

Most have heard of spirolocks and other methods of wrist-pin retention, but when it comes to all-out racing, wrist pin buttons reign king of strength and simplicity. 
When the application calls for a sturdy, full-round piston in a high-performance engine, wrist-pin buttons have long been an option for keeping the piston secured to the connecting rod. In some piston designs where the wrist-pin bore invades the oil-ring groove, these buttons can actually force a kink to the oil rings under extreme stress. But a new, patented wrist-pin button from Wiseco is helping to eliminate the impacts that destroy those rings and, therefore, extend the engine’s lifecycle.

“We’ve been using it on Pro Mods and Radials vs. The World cars for two, three years now,” says Wiseco technical sales associate Vic Ellinger. “Everyone who has them has alleviated a lot of issues that they had before with conventional buttons.”

Engine builders who service today’s high-horsepower racing engines on a regular schedule have always been grateful for wrist-pin buttons and the time they save in the shop or pits. Not only does the piston and ring assembly come apart and go together quicker, there’s also a lot less bloodshed by not having to remove and install four sharp-edged Spirolox retaining clips needed on every piston. Aside from the time factor, the pin can “plow” open the groove that supports the Sprirolox or cnap ring and increase the side clearance.

“Buttons maintain end play of the pin,” says Ellinger. “It lets the pin float freely and not bind against the clips. A design utilizing clips won’t float as easily if the stack-up tolerances of the pin, lock-ring spacing and clipsare on the tight side, and the parts are expanding rapidly during the course of a run. Asthe pin is hammering the buttons side to side, it’s not going to open up that side clearance more than a few thou during a season.”

There is a potential downside, however, to using pin buttons when the wrist-pin bore actually cuts into the oil-ring groove and interferes with a portion of the support surface that ring land provides. Unfortunately, this design option is needed on pistons with short compression heights where the engine builder is using the longest connecting rod possible. Or it’s used in high-boost or nitrous applications where the ring grooves are moved away from the heat in the piston crown, or the lower location is needed to increase the strength of the crown area.

The wrist-pin buttons designed for these applications are machined with a slot that matches the oil-ring groove of the pistons. The oil ring can be installed alone or with a support rail. These oil-ring support rails never come into contact with the cylinder wall and have no effect on lubrication. Their sole purpose is to stabilize the oil ring pack, and they are designed with dimples in strategic locations to keep them from rotating inside the ring groove. Problems, however, can arise when the wrist-pin buttons twist inside the pin bores and pinch the oil ring and its support rail.

“With nitrous, it shocks the button so hard, that it actually kinks the scraper and locks up the oil ring. It’s like you stuck them in a vice. Right where the button would hit the rail, it would have a big kink mark in it,” says Ellinger. “Just kicks it right up and it looks like you hit it with a chisel.”

Wiseco’s solution to prevent the buttons from twisting and damaging the oil ring is to machine a pair of dog-ear-shaped dowels—one on each side of the button. These dowels match up with a pair of receiver notches that are machined into the pin bore.

“When the button drops in, it can't move and rotate in the bore. Then you can also eliminate the oil rail support, which gives you an extra inch worth of ring land to use wherever you need it, especially for boost or nitrous,” explains Ellinger. “That's basically the reason, it won't kink the scraper and you free up real estate on the ring lands."

The new buttons with the D-shaped ears are machined from or billet alloy to match the construction of the pistons. The corresponding receiver slots are plunged cut on a hand mill. The buttons are designed to allow lateral movement as needed for the clearances, but the design eliminates any rotation within the pin bore. The recommended clearance between the pin, buttons and cylinder wall is dependent on a variety of factors, including bore size, pin size and piston material.

“All that has to be taken into account. And we like to see, depending on the application, it could be as tight as inch or as loose as , even inch,” says Ellinger. “It just depends on what the specs are of the motor, and the type of application. If it's Bonneville, that's going to need something different where they're chilling the engines to rather cold engine tempsand immediatelyputting them into extreme conditions. You have to take into account how fast the parts are going to grow.

“The bore size is going to determine what end play you have with the length of the button, so your stack-up tolerances are going to give you what your number is,” continues Ellinger. “But, obviously, the stack-up tolerances can cause some variance with the manufacturer of the pin, or what brand pin. Also, if you open up the bore to allow for more clearance for a high-horsepower application, that's something that needs to be known during the design phase. If you're plus-one, plus-two, three-thousandths over what the nominal bore size is, we've got to compensate for that with the pin bore.”

The clearance for the buttons and pins is calculated based on the final bore size, length of the pin and a target side clearance. For example, a inch bore matched with a inch-long pin and a desired inch end play = X clearance. Wiseco engineers can then calculate the required length for each button.

“The dowels are free floating, probable to inch clearance. Most guys just install the piston upside down without the rod and give it a wiggle test. An experienced hand can tell if something is awry,” adds Ellinger. “Some actually assemble the parts and measure the overall length of the pin and buttons and make sure it has at least less than the bore size for a measured length.”

Obviously the use of a wrist pin button requires a full-round piston so that the bottom side of the button has a shelf upon which to rest. Some engine builders may be leery of the extra weight that comes with pin buttons, so Wiseco rifle-drills a hole through the pin axis of the button.

“And we lighten them up on the backside, if we can,” adds Ellinger. “But typically, with these applications, they're more like diesels as far as the strength that's needed. The weight isn't an issue, because the rod and the crank are usually also fit for use. So, the rods are beefier. The cranks are better quality billet. So all that just kind of depends on just the power level, but typically the weight isn't an issue with those type of builds as they are with a naturally aspirated deal.”

Ring choice may be a little more flexible with the use of the new Wiseco pin buttons, but there are limitations due to the engine size and use.

 “You really want to lean towardshigher-tension oil rings just because of the swept area of oil volume you have to try to control, especially with a setup like inch pistons and inch stroke,” explains Ellinger. “I mean, there's just so much oil up there sloshing aroundthat they really need to be able to keep that oil off those cylinder walls as much as possible, and have it controlled. Because they're only on the gas for four seconds, three seconds, and they're really hard to control all that oil while it's surging up the back cylinder walls.”

Although pin buttons are used most often on high-end, frequently serviced race engines, they’re also suitable for many other applications.

“No, you can use it in any application, really, motorcycle, car, boat. The highest horsepower stuff is usually where we put it but you could even use it in a bracket engine,” says Ellinger. “There are a lot of benefits to it because it's the closest thing you can get to a true, non-stroker style piston design for a stroker. We've even used them where we've gotten into the second ring groove. We had to machine a second ring groove and an oil groove into the button because we lowered the lands to increase the strength of the piston, like a Top Fuel part would be.

“Wrist-pin buttons are really simple,” sums up Ellinger. “There's nothing there other than getting the things to quit ruining really expensive ring packs. That's really what they've done is brought oil consumption under control and eliminated the need for an oil rail support to add inch worth of ring land to where you need it most, up top.”

Sours: http://blog.wiseco.com/what-are-wrist-pin-buttons

Pin wiseco wrist

Wrist pin offset is a useful tool used by OEM and aftermarket piston engineers alike. Here's an explanation of the process and why it's done. 

On the surface it seems quite logical that the piston pin bore would be centered in the cylinder bore of any internal combustion engine. Having the cylinder axis intersect the crank axis is a time-honored tradition among engine designers. It has been the normal practice in production engines for well over a century, but time has a way of adjusting our thinking to newer and better ways.

As engines evolved, engineers determined that offsetting the piston (wrist) pin yields two major benefits. First, it improves the noise characteristics of the engine due to piston slap at top dead center (TDC). This is a major NVH (noise vibration and harshness) concern to production engineers who want to eliminate alarming noises anywhere they can. The second reason is to improve engine output by reducing internal friction.

Offsetting the cylinder axis from the crankshaft axis, minimizes rod angularity when cylinder pressure is at its highest. Reduced angularity leads to lower piston thrust forces, hence lower frictional losses during the period of maximum cylinder pressure, especially at the beginning of the power stroke when pressure rises sharply about 12-15 degrees after TDC. Rather than revising a complete engine design, the easy way to do this is to offset the pin bore in the piston. This allows the same crank/rod pin axis geometry as an engine designed with offset cylinder axes, but within existing conventional engine architecture.

 

The amount by which the cylinder axes need to be offset depends on many variables, but the main ones are the ratio of crank throw to con rod length and the angle after TDC at which maximum cylinder pressure occurs. Moving the pin bore is more practical Wiseco Pistons have determined that a pin bore offset of 0.050-inch is enough for most applications. They are also aware of the effect on engine stroke length due to offsetting the pin bore. Offsetting the pin bore slightly increases the stroke which may be enough to throw the engine out of spec for some racing classes that limit displacement visa bore or stroke.

Moving the pin bore enjoys a similar benefit to adding rod length in that it slows the piston speed at TDC thus allowing a longer period for flame propagation to build cylinder pressure before the power stroke really gets under way. The tradeoff is higher velocity approaching TDC and lower velocity departing TDC which may affect fuel octane requirements. While not as beneficial on short track applications, it does offer an advantage on longer tracks or in drag racing and Bonneville applications. The improved leverage angle while maintaining TDC is still important. Delaying pressure while the crank moves to a better leverage angle will help increase torque particularly at low rpm.  It should be noted that the effects are minimal but nonetheless found to be beneficial when they are applied in max effort applications.

A lot of mathematical calculation goes into the slider/crank relationship regarding pin bore offset, but Wiseco engineers have calculated the optimum amount of offset for performance applications and apply it where required. Special fixtures are used to accurately offset the pin bores. For pins that also intersect the oil rig groove, offset pins do not compromise oil ring function since the oil rings use a support rail for stability. The effects on rod loading are minimal as most modern connecting rods easily handle the loads. In supercharged cases, strong rods are typically included in the build as a matter of course.

Sours: http://blog.wiseco.com/what-is-wrist-pin-offset
Bottom End Buyers Guide - How to Choose the RIGHT Pistons Rods Bearings Studs Gaskets Cranks Sleeves

Wiseco Piston Wrist Pin mm Standard Bore for Honda CRR

Wiseco Piston Wrist Pin mm Standard Bore for Honda CRR

Wiseco Piston Wrist Pin mm Standard Bore for Honda CRR

Wiseco Piston Wrist Pin mm Standard Bore for Honda CRR

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Sours: https://woncacom/nxoya-CRR-Wiseco-Piston-Wrist-Pin/Motorcycle-Parts/

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Wiseco Piston Wrist Pin
# S


 
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Material:
Length:
Option:
Style:OEM Replacement
Outside Diameter:mm
Note: Compression. Cylinder boring required for oversizes - Replacement Wrist Pin
Inside Diameter:mm
Type:Wrist Pin
Normally ships in business days
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on this item within

Continental USA

some restrictions apply

  • Wiseco wrist pins are strong, lightweight and can be used with OEM pistons, too

 
This item fits the following models:
 
Honda CRFF -
Honda CRF50F -
Honda CRF70F -
Honda CRF80F - (see fitment notes)
Honda XR50R -
Honda XR70R -
Honda XR80 - (see fitment notes)
Honda XR80R -
Honda Z50R -
Kawasaki KLX - (see fitment notes)
Kawasaki KLXL -
Suzuki DR-Z -
Yamaha TTR90
Yamaha TTR90E -
Yamaha YFM80 Badger -
Yamaha YFM80 Grizzly -
Yamaha YFM80W Raptor -

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Shipping weight: lbs
Shipping size (L x W x H): x x inches
Style: OEM Replacement
Outside Diameter: mm
Note: Compression. Cylinder boring required for oversizes - Replacement Wrist Pin
Inside Diameter: mm
Type: Wrist Pin
Made in JP
Sold as: EA

This item fits the following vehicles:
Honda CRFF
Honda CRFF
Honda CRFF
Honda CRFF
Honda CRFF
Honda CRF50F
Honda CRF50F
Honda CRF50F
Honda CRF50F
Honda CRF50F
Honda CRF70F
Honda CRF70F
Honda CRF70F
Honda CRF70F
Honda CRF70F
Honda CRF70F
Honda CRF70F
Honda CRF70F
Honda CRF70F
Honda CRF70F
Honda CRF70F
Honda CRF80F
Honda CRF80F
Honda CRF80F
Honda CRF80F
Honda CRF80F
Honda CRF80F
Honda CRF80F
Honda CRF80F
Honda CRF80F
Honda CRF80F
Honda CRF80F 1
Honda CRF80F 1
Honda CRF80F 1
Honda CRF80F 1
Honda CRF80F 1
Honda CRF80F 1
Honda CRF80F 1
Honda CRF80F 1
Honda CRF80F 1
Honda CRF80F 1
Honda CRF80F 1
Honda CRF80F 1
Honda XR50R
Honda XR50R
Honda XR50R
Honda XR50R
Honda XR70R
Honda XR70R
Honda XR70R
Honda XR70R
Honda XR70R
Honda XR70R
Honda XR70R
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80 1
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda XR80R
Honda Z50R
Honda Z50R
Honda Z50R
Honda Z50R
Honda Z50R
Honda Z50R
Honda Z50R
Honda Z50R
Honda Z50R
Honda Z50R
Honda Z50R
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLX 1
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Kawasaki KLXL
Suzuki DR-Z
Suzuki DR-Z
Suzuki DR-Z
Yamaha TTR90
Yamaha TTR90E
Yamaha TTR90E
Yamaha TTR90E
Yamaha TTR90E
Yamaha TTR90E
Yamaha TTR90E
Yamaha TTR90E
Yamaha TTR90E
Yamaha TTR90E
Yamaha TTR90E
Yamaha TTR90E
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Badger
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80 Grizzly
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
Yamaha YFM80W Raptor
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Yamaha YFM80W Raptor
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[1]
Cylinder boring required

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