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Found 5 results

  1. When it comes to overall strength, there's no beating a forged piston. But what is the process that yields the toughest parts in the racing world? We'll show you. When it comes to turning raw metal alloys into useful things, two processes dominate - casting and forging. Both have their place, but when strength and light weight are priorities, forging is the method of choice. Though it’s been around for more than six millennia, forging processes continue to advance the state of the art, bringing us everything from sharper, more durable kitchen knives to more fuel efficient jet engines, plus things much closer to our heart: lighter, stronger pistons. Although forging is a metalworking process thousands of years old, it’s still the best method to produce components with the highest strength and durability. Forging is defined as the controlled deformation of metal into a desired shape by compressive force. At its most basic, it’s a blacksmith working a piece with a hammer and anvil, and those first metalworkers toiling at their forges discovered something important about the pieces they were crafting – compared to similar objects made from melted and cast metal, they were stronger and more durable. Though they knew the finished product was superior, what those ancient smiths didn’t suspect was that the act of forging was changing the internal grain structure of the metal, aligning it to the direction of force being applied, and making it stronger, more ductile, and giving it higher resistance to impact and fatigue. While a cast metal part will have a homogeneous, random grain structure, forging can intentionally direct that structure in ways that give a finished part the highest structural integrity of any metalworking process. Wiseco forged pistons start as raw bar stock in certified 2618 or 4032 aluminum alloy. Once they’re cut into precisely-sized ‘pucks’ they’re ready to be preheated in preparation for forging. Although many performance enthusiasts might put billet parts at the top of the heap in terms of desirability, the reality is that the billet they are created from doesn't have the same grain properties of a forging. The Wiseco Forging Process Today’s state of the art in forging technology is far removed from the smith’s bellows-stoked fire and anvil. In Wiseco’s ISO 9000-certified forging facility, pistons begin life as certified grade aluminum bar stock, cut to precise lengths to form slugs. The choice of material is critical - conventional wisdom has always said that a forged piston requires additional piston-to-bore clearance to allow for expansion, leading to noise from piston slap until the engine gets up to temperature, but per Wiseco’s Research and Development Manager David Fussner, “Forged pistons do require additional room temperature clearance. However, the 4032 forging alloy we use has about 12% silicon content, and this significantly controls the expansion to nearly the same as a 12% silicon cast piston. The 2618 alloy expands a bit more and does require a bit more room temperature clearance than 4032.” Pistons are forged in a ‘backwards extrusion’ process where a moving punch presses the raw material into the die to form the rough shape. The process takes only a fraction of a second (longer in the isothermal press), and the speed of the press helps determine how material flows, and therefore the internal grain structure of the forging. While 4032 is more dimensionally stable across the typical operating temperature range seen inside an engine, it does give up a small advantage in ductility to 2618, which has a silicon content of less than 0.2 percent. This makes 2618 a better choice for applications where detonation may be an issue, like race engines running high boost or large doses of nitrous oxide. The low silicon alloy’s more forgiving nature in these instances makes up for the tradeoffs in increased wear and shorter service life compared to 4032. Once cut to the proper size, slugs are heated to a predetermined temperature and moved to the forging press itself, which is also maintained at a controlled temperature. There are two different types of presses employed at Wiseco; mechanical and hydraulic. Both have a long history in manufacturing, and each has specific strengths. Mechanical forging presses are well-suited to high production rates, helping to keep the overall cost of high-quality forged components affordable. Hydraulic presses have the advantage of variable speed and force throughout the process, allowing greater control of material flow, which can be used to produced forged components with even more precisely controlled physical properties. Wiseco’s isothermal hydraulic press forging machines use precise digital control of the temperature of the raw material, the punch, and the die, as well as the pressure exerted during the full motion of the forge. This allows very close control over the physical properties of the finished forging. Regardless of the type of press, pistons are forged using a “backwards extrusion” process where the material from the slug flows back and around the descending punch to form the cup-shaped forging. Picture the stationary part of the press (the die) as the mirror image of the piston top, and the punch as the mirror image of the underside. As the punch descends, the puck is transformed into the rough piston shape with material flowing up along the sides of the die and punch to form the skirt. This entire process takes place on the scale of milliseconds (on the mechanical press), and the all-important flow stresses of the material are determined by the strain rate (or speed) and load applied by the press. In addition to three mechanical forge presses, Wiseco also has two isothermal hydraulic presses in-house. These state of the art forges maintain the temperature of the piston slug, the die, and the punch very accurately through computer control, delivering more precise dimensions and geometry for the finished pieces, as well as allowing for more complex designs to be successfully forged, and even the creation of metal matrix composite forgings. Once the puck (left) has been transformed into a forged blank (middle), it still has a ways to go before becoming a completed piston (right). The Heat Is On Once the forging process is complete, the components next move to heat treatment. Wiseco’s aerospace-grade heat treatment facility is located in the same plant as the presses, and here the pistons go through a carefully controlled process of heating and cooling that relieves stress induced during forging, increases the overall strength and ductility of the metal, and provides the desired surface hardness characteristics. While casting can deliver parts straight out of the mold that are very close to their final shape, forgings require a bit more attention in order to get them into shape. Fussner explains, “In a dedicated forging for a specific purpose, the interior of the forging blank is at near-net as it comes off the forging press. And in some cases, we also forge the dome near-net with valve pockets and some other features. Other than these items, most other features do require machining.” Pistons aren't the only thing Wiseco forges and machines in-house. Wiseco clutch are also forged and machined, as well as finished with hard anodizing. The forging (left) allows the basket to closer to the final shape before machining. The basket shown here is just post-machining. One basic forging may serve as the starting point for many different types of finished pistons, unlike castings which are typically unique to a single design or a small group of very similar designs. Regardless of the manufacturing method for the piston blank, some degree of final machining needs to take place to create a finished part. “As a ballpark percentage, I would say about 75% of the forging blank would require machining.” Cast pistons also require finish work on the CNC machine, but this is almost always less extensive than a similar forged piston. “That’s the main reason why forged pistons are more expensive than a cast piston,” Fussner adds. Another reason for the added expense of forging is the significant cost of the initial tooling for the die and punch, which must be made to exact specifications and be durable enough to survive countless forging press cycles. Per Fussner, “We control these costs by making all our forging tooling in house at Wiseco headquarters in Mentor, Ohio.” The ability to make their own tooling, doing their own forging, and their in-house heat treatment facilities make Wiseco the only aftermarket forged piston manufacturer in the United States with these unique capabilities. Once the machining process is complete, Wiseco pistons can also receive a number of different proprietary coatings to fine-tune their performance. These include thermal barriers as well as wear reduction treatments. Though forging is a technique literally as old as the Iron Age, it’s still the undisputed king of manufacturing techniques for light, strong, durable components. Wiseco continues to refine the process with the latest methods, materials, heat treatment, and machining to provide the highest quality aftermarket components available, at an affordable price. Wiseco forged pistons provide superior quality and performance at an affordable price thanks to the company’s close control over every step of the manufacturing process.
  2. Attention two-stroke riders! For a limited time, Wiseco is offering to let you choose up to two FREE items with proof of two-stroke piston(s) purchase! Read on for all the details on this offer. Who doesn't love the sound, smell, and fun of a two-stroke? Wiseco has a new rebate offer just for the two-stroke lovers! For a limited time, Wiseco will be offering your choice of up to TWO (2) different free items with a minimum purchase of any off-road bike or ATV Wiseco two-stroke shelf piston(s)! Choose from our new high-quality, modern-fit Wiseco T-shirts, the new Wiseco Patch hat, or a top end gasket kit! Simply pay a flat $10 shipping fee. Click here to go to the Two-For-Two-Stroke rebate form! How does the rebate work? To participate, follow the instructions below. Purchases must be made between TWOsday August 28th and TWOsday October 30th, and redeemed by November 30th. Purchase a minimum of $118 of any new off-road bike or ATV Wiseco two-stroke shelf piston(s) for ONE (1) FREE item, or a minimum of $165 for TWO (2) FREE items. Save your receipt/proof of purchase and piston box. Scan or take a photo of the proof of purchase and the piston box label showing the part number, and upload to the online rebate form. Click here to go to the online rebate form, fill it out completely with all required information, be sure photos from step 3 are uploaded, and submit. Allow 1-2 business days to be contacted by a Wiseco representative, pay a flat $10 shipping fee, and allow 4-6 weeks for your free item(s)! This is an example of the piston box label you will need to upload a photo of. The free item options include our new, high-quality modern-fit T-shirts! Click here to find Wiseco two-stroke pistons for your application! All Wiseco two-stroke pistons are forged in-house for added strength and durability, and are available for wide variety of applications. Wiseco Two-Stroke Racer Elite Wiseco's latest development in two-stroke piston technology is the Two-Stroke Racer Elite piston. These pistons are forged from a 2000 series alloy for additional strength qualities, and protected by Wiseco's ArmorPlating coating on the piston crown and in the ring groove(s) for long-term protection from corrosive combustion chamber conditions. Watch the video and get the complete details on Two-Stroke Racer Elite HERE. Don't forget! Some two-stroke pistons require exhaust bridge lubrication holes to be drilled in the piston, and the exhaust bridge on the cylinder to be relieved. Not sure if you need this, or need help completing these tasks? We explain it all HERE. Do you know the importance of exhaust bridge relief and lubrication holes? Review our full explanation here! Check out some more of our awesome two-stroke content! Dirt Bike Mag YZ125 Build 80+ HP Two-Stroke Karts Wiseco Employee-Built 390cc TRX KTM TPi Two-Stroke Pistons What is a Locating Pin? Wiseco "Two-For-Two-Stroke" Rebate Terms & Conditions Purchase at least $118 worth of any offroad bike or ATV Wiseco two-stroke shelf piston(s) from any dealer or retailer between August 28, 2018 and October 30, 2018 and receive your choice of one out of four available items, or purchase at least $165 under the same stipulations above for your choice of two out of four available items, after online form submission. When applicable, two chosen items must be different, one item cannot be doubled-up. Wiseco two-stroke piston kits and PK kits eligible. Purchased dollar amount minimum must be met completely by Wiseco two-stroke piston product. $10 shipping fee applies to free items. Final shirt and hat colors and designs may not exactly reflect items pictured in promotion images. Promotion does not apply to custom pistons. Minimum purchase amounts at retail value only. Rebate form must be submitted electronically at www.wiseco.com/promo with all required information. Must provide photos or scan of proof of purchase and piston box label showing part number. Allow 4-6 weeks to receive your chosen items. Offer must be redeemed by November 30, 2018. Offer good only in 48 contiguous states. Limit one rebate per eligible purchase, per household. Maximum number of free items is two. Free gasket kit limited to a retail value of $69.00. P.O. Box address not accepted. Must be 18 years of age. This rebate offer is valid for end consumers only and not available to distributors, dealers, resellers, retailers or e-tailers. Offer void where prohibited, taxed or restricted by law. Please keep a copy of your submission. Substitution of products not valid. Qualifying products cannot be returned to the retailer once the rebate form has been submitted. Offer has no cash value. No substitutions. Void where prohibited by law.
  3. Rob@ProX

    How-To: 4-Stroke Piston Replacement

    We have a used 2006 YZ450F that we're rebuilding step-by-step, and documenting along the way. In this part 1 feature, we'll go over how to replace a 4-stroke piston. Click here to watch the quick tip video to go along with it! The top end in a four-stroke can be split up into two major sections: the head, and the cylinder and piston. They both require specific attention and critical steps to ensure proper opertation once everything is back together. We replaced the worn stock piston with an OEM quality forged ProX piston kit. It includes the rings, wrist pin, circlips, and installation instructions. The pistons are available in A, B, and C sizes, to accomodate for the size of your cylinder as it wears. Our new ProX forged piston compared to the stock, used piston. Carbon deposits on the crown are common after running hours, but can decrease power and efficiency. Disassembly To prepare to disassemble your head and cylinder, you'll need to remove the seat, gas tank, exhaust system, and carburetor (or throttle body). While not always required, removing the sub-frame, shock, and air boot make accessibility to the engine a lot easier in most cases. Once those major components are removed, you'll need to remove any other components attached to the head or cylinder, such as clutch cable guides, spark plug boots, and electrical connections. Removing the subframe, airboot, and shock, in addition to the other components, provides much better access to all sides of the motor. Don't forget to remove any cable guides or other items bolted to the head/cylinder. Next, remove the cam cover, loosening the bolts incrementally until they are all loose. With that off, it is best to make sure your camshafts are not fully compressing any of the valve springs before you loosen the cam caps. You can do this by slowly rotating the crankshaft via the kickstarter. With the cam caps removed, loosen and remove the cam chain tensioner next. This will give you the slack to remove the timing chain completely. You can now lift the camshafts completely out, handling carefully. Now you can loosen the head bolts in incrementally in a crossing pattern. Remove the head and place it aside, handling it carefully. Next, do the same for the cylinder bolts, and carefully remove the cylinder. As you remove the cylinder, the piston is going to stay on the connecting rod, so it helps to hold the connecting rod steady as you wiggle the cylinder off the piston. It is always a good idea to fill the opening of the cases with a lint free rag to prevent debris or loose parts from falling in. Remove the cam cover and head bolts incrementally until loose. This prevents the chance of warping. Finally, you can remove one wire lock from the stock piston using a pick or small screwdriver. Slide the wrist pin out, and remove the piston from the small end of the connecting rod. Be very careful no to drop anything into the cases during this step, and throughout the entire process. Cleaning With everyting removed, you'll need to clean any old gasket material and other residue off your sealing surfaces. This includes the base for the cylinder on the cases, top and bottom surfaces of the cylinder itself, and the bottom surface of the head that seals to the cylinder. For large or difficult pieces of material, it is common to use a razor blade for removal. However, be gentle and careful not to put deep grooves or scratches in the surfaces. Also, don't cut your finger open, or off. Scrape old gasket material off carefully, being cautious of any grooves or scratches in sealing surfaces and personal injury. Final cleaning commonly consists of using carb cleaner, or a similar chemical cleaner, and a rag to achieve completely clean and flat surfaces. Cylinder Prep Before you go and put that cylinder back in with your new piston, you'll want to inspect it for signs of wear, and measure it to make sure it's within spec (refer to your owner's manual for proper specifications). If there is minimal glazing on the cylinder, no grooves worn in, and it's within spec, you should be ready to reinstall after a good honing. Always use a diamond tipped honing brush for resurfacing work. If you're unsure about performing any cylinder prep work yourself, talk to your local dealer about cylinder shops, where any prep work required can be performed. ProX pistons are available in multiple sizes to accomodate for cylinder wear, so be sure your bore measurements correlate with the size of piston you're installing. Make sure your cylinder is the correct bore size for your piston, and properly cleaned and honed, as pictured here. Reassembly When you have your cylinder prepped and ready, now is a good time to double check your piston-to-wall clearance and ring end gap. For piston-to-wall, measure the size of your ProX piston using a micrometer only. Measure the piston on the skirt, 90 degrees from the wrist pin bore, at the point on the skirt that is 1/4 of height of the piston from the bottom. Refer to your manual for acceptable piston-to-wall clearance range. When measuring ring end gap, install the top ring and second ring (seperately, and if applicable) approximately 1/4" into the bore. Use a feeler gauge to be sure ring end gap is within the dimensions specified in your piston kit instructions. ProX rings are pre-gapped, but it is always good practice to double check. While ProX rings are pre-gapped, it's still a good idea to double check your ring end gap. Install the rings in the proper order and location on your pistons. Refer to the instructions that come with ProX piston kits to be sure you are installing the rings in the correct fashion and location. After this, install one wire lock into your piston, being sure it is properly seated. Click here for our tips on installing wire locks. Use your finger to put a layer of motor oil on the cylinder wall. Next, put a layer of oil on the outside of your new piston (on the outside of the rings, on the ring belt, and on the skirts). You don't want your new piston and rings breaking in under dry conditions. Use the normal motor oil you use in your 4-stroke. Piston installation can be done via more than one method, but in our case, we installed the piston in the cylinder before attaching it to the connecting rod. Either way, be sure your piston is facing the correct direction, meaning the exhaust valve reliefs line up with the exhaust side of the head. There will be markings on the crown of ProX pistons to indiciate which side is the exhaust side. Also, make sure your rings remain in the proper location as you slide the piston into the cylinder. The arrow shows the marking on the piston crown that indicates that is the side of piston that needs to face the exhaust. Before installing the new base gasket, piston and re-installing the cylinder, make sure the surface is clean and the crankcase is free of debris. While the top end is off, this could also be a good time to make sure your crankshaft is in spec. Next, lay your new base gasket on the cases, lining it up properly. Install the piston (which should remain in the cylinder) onto the connecting rod by lining up the pin bore with the small end bore, and sliding your new wrist pin (put a layer of oil on this before installing) completely through, until it stops against the one wire lock previosuly installed. With the piston secured to the connecting rod via the wrist pin, install your remaining wire lock, and make sure it is properly seated. You can now slide the cylinder all the way down to meet the cases. Note: Make sure you take any rags out of the cases before reassembling! You're now at the point in reassembly where you will install your rebuilt head (details in part 2 of this top end rebuild soon to come) with the proper head gasket, and re-install all the items previously removed. Be sure you are following all proper torque specs specified in your manual. Head back for part 2 of the the top end rebuild, where we'll show you some great tips on assembling a four-stroke head with new valves and valve springs, re-installing camshaft(s) and timing chain, and checking and adjusting valve clearance. Our new ProX piston and freshened up clyinder successfully installed. Note the dot on the piston crown, indicating that is the exhaust side. Stay tuned, more rebuild tips to come!
  4. Whether you're racing or looking for increased performance out on the trail, there are a plethora of performance upgrades to consider to increase the power of your machine. Piston manufacturers like JE Pistons offer high compression piston options for many applications, but there are important merits and drawbacks you should consider when deciding if a high compression piston is right for your application. To better understand, we’ll take a look at what increasing compression ratio does, what effects this has on the engine, detail how high compression pistons are made, and provide a high-level overview of which applications may benefit from utilizing a high compression piston. Bumping up the compression in your motor should be an informed decision. It's important to first understand what effects high-compression has, the anatomy of a high-comp piston, and what applications typically benefit most. Let’s start with a quick review of what the compression ratio is, then we’ll get into how it affects performance. The compression ratio compares the volume above the piston at bottom dead center (BDC) to the volume above the piston at top dead center (TDC). Shown below is the mathematical equation that defines compression ratio: The swept volume is the volume that the piston displaces as it moves through its stroke. The clearance volume is the volume of the combustion chamber when the piston is at top dead center (TDC). There are multiple different dimensions to take into account when calculating clearance volume, but for the sake of keeping this introductory, this is the formula as an overview. When alterations to the compression ratio are made, the clearance volume is reduced, resulting in a higher ratio. Reductions in clearance volume are typically achieved by modifying the geometry of the piston crown so that it occupies more combustion chamber space. Swept volume is the volume displaced as the piston moves through the stroke, and clearance volume is the volume of the combustion chamber with the piston at top dead center. How does an increased compression ratio affect engine performance? To understand how increasing the compression ratio affects performance, we have to start with understanding what happens to the fuel/air mixture on the compression stroke. During the compression stroke, the fuel/air mixture is compressed, and due to thermodynamic laws, the compressed mixture increases in temperature and pressure. Comparatively, increasing the compression ratio over that of a stock ratio, the fuel/air mixture is compressed more, resulting in increased temperature and pressure before the combustion event. The resulting power that can be extracted from the combustion event is heavily dependent on the temperature and pressure of the fuel/air mixture prior to combustion. The temperature and pressure of the mixture before combustion influences the peak cylinder pressure during combustion, as well as the peak in-cylinder temperature. For thermodynamic reasons, increases in peak cylinder pressure and temperature during combustion will result in increased mechanical efficiency, the extraction of more work, and increased power during the power stroke. In summary, the more the fuel/air mixture can be compressed before combustion, the more energy can be extracted from it. Higher compression allows for a larger amount of fuel/air mixture to be successfully combusted, ultimately resulting in more power produced during the power stroke. However, there are limits to how much the mixture can be compressed prior to combustion. If the temperature of the mixture increases too much before the firing of the spark plug, the mixture can auto ignite, which is often referred to as pre-ignition. Another detrimental combustion condition that can also occur is called detonation. Detonation occurs when end gases spontaneously ignite after the spark plug fires. Both conditions put severe mechanical stress on the engine because cylinder pressures far exceed what the engine was designed for, which can damage top end components and negatively affect performance. Detonation and pre-ignition can spike cylinder pressure and temperature, causing damage. Common signs of these conditions include pitting on the piston crown. Now that there is an understanding of what changes occur during the combustion event to deliver increased power, we can look at what other effects these changes have on the engine. Since cylinder pressure is increased, more stress is put on the engine. The amount of additional stress that is introduced is largely dependent on the overall engine setup. Since combustion temperatures increase with increased compression ratio, the engine must also dissipate more heat. If not adequately managed, increased temperatures can reduce the lifespan of top-end components. JE's EN plating is a surface treatment that can protect the piston crown and ring grooves from potential damage caused by high cylinder pressure and temperature. EN can be an asset for longevity in a high-compression race build. Often, additional modifications can be made to help mitigate the side effects of increasing the compression ratio. To help reduce the risk of pre-ignition and detonation, using a fuel with a higher octane rating can be advantageous. Altering the combustion event by increasing the amount of fuel (richening the mixture) and changing the ignition timing can also help. Cooling system improvement can be an effective way to combat the additional heat generated by the combustion event. Selecting larger or more efficient radiators, oil coolers, and water pumps are all options that can be explored. Equipping the engine with a high-performance clutch can help reduce clutch slip and wear which can occur due to the increased power. High-level race team machines are great examples of additional modifications made to compensate for increased stress race engines encounter. Mods include things like larger radiators, race fuel, custom mapping, and performance clutch components. Let’s take a quick look at what considerations are made when designing a high compression piston. Typically, high compression pistons are made by adding dome volume to the piston crown, which reduces the clearance volume at TDC. In some cases, this is difficult to do depending on the combustion chamber shape, size of the valves, or the amount of valve lift. When designing the dome, it is essential to opt for smooth dome designs. Smooth domes as opposed to more aggressively ridged designs are preferred because the latter can result in hot spots on the piston crown, which can lead to pre-ignition. Another common design option is to increase the compression distance, which is the distance from the center of the wrist pin bore to the crown of the piston. In this approach, the squish clearance, which is the clearance between the piston and head, is reduced. Higher compression is commonly achieved by increasing dome volume while retaining smooth characteristics, as pictured here with raised features and deep valve pockets. Compression height can also be increased, which increases the distance between the center of the pin bore and the crown of the piston. A high-level overview of which applications can benefit from increased compression ratio can be helpful when assessing whether a high-compression upgrade is a good choice for your machine. Since increasing the compression ratio increases power and heat output, applications that benefit from the additional power and can cope with additional heat realize the most significant performance gains. Contrarily, applications where the bike is ridden at low speed, in tight conditions, or with lots of clutch use can be negatively impacted by incorporating a high compression piston. Keep in mind these statements are generalizations, and every engine responds differently to increased compression ratios. Below are lists of applications that may benefit from increasing the compression ratio as well as applications where increased compression may negatively influence performance. Applications that may benefit from utilizing a high compression piston: Motocross Supermoto Drag racing Road racing Ice racing Flat track Desert racing Motocross and less technical off-road racing are two of multiple forms of racing in which high-compression pistons can benefit performance due to higher speeds and better air flow to keep the engine cool. Peick photo by Brown Dog Wilson. Applications that may be negatively affected by utilizing a high compression piston: Technical off-road/woods riding Trials Other low speed/cooling applications Lower speed racing and riding may not benefit as much from a high-compression piston, as heat in the engine will build up quicker due to lessened cooling ability. Fortunately, if you’re considering increasing your engine’s compression ratio by utilizing a high compression piston, many aftermarket designs have been tested and optimized for specific engines and fuel octane ratings. For example, JE Pistons offers pistons at incrementally increased compression ratios so that you can incorporate a setup that works best for you. For example, high-compression pistons from JE for off-road bikes and ATVs are commonly available in 0.5 compression ratio increases. Assume an engines stock compression ratio is 13.0:1, there will most likely be options of 13.5:1 and 14.0:1, so that you can make an informed decision on how much compression will benefit you based on your machine and type of riding. From left to right are 13.0:1, 13.5:1, and 14.0:1 compression ratio pistons, all for a YZ250F. Notice the differences in piston dome volume and design. If performance is sufficient at an engine’s stock compression ratio, there are still improvements in efficiency and durability that can be made with a forged piston. Forged pistons have a better aligned alloy grain flow than cast pistons, creating a stronger part more resistant to the stresses of engine operation. In addition to forged material, improvements can be made on piston skirt style design to increase strength over stock designs, such as with JE’s FSR designs. JE also commonly addresses dome design on stock compression pistons, employing smoothness across valve reliefs edges and other crown features to improve flame travel, decrease hot spots, and ultimately increase the engine’s efficiency. Even if stock compression is better for your application; forged construction, stronger skirt designs, and more efficient crown designs can still provide improved performance and durability. If it’s time for a new piston but you’re still not sure what compression ratio to go with, give the folks at JE a call for professional advice on your specific application.
  5. Find out how to relieve an exhaust bridge and drill lubrication holes in 2 stroke applications, so you can get the most out of your piston! When you order a new Wiseco 2-stroke piston and open up the box and read the instructions, you might see something like “follow these steps to drill the lubrication holes.” There’s no doubt that the thought of drilling holes in your new piston can be scary and intimidating. But not to worry! We’ll get you through it right here with all the information you need and a step-by-step. Relieving the exhaust bridge and drilling lubrication holes is a common part of the 2-stroke top end replacement process, but the importance of performing these steps is unrealized by many and neglected too often. Drilling lubrication holes is a simple but important process for many 2 stroke applications. So, what is an exhaust bridge? First things first, not all 2-stroke cylinders have an exhaust bridge. So if your cylinder does not have one, drilling holes in your piston is not necessary. The exhaust bridge is the thin strip of metal that separates the exhaust ports in the cylinder. Whether you look into the exhaust ports through the exhaust outlet or through the cylinder bore, if you see a thin metal wall separating your exhaust ports, that is your exhaust bridge. For the purpose of installing a new Wiseco piston, the area of concern is the edge of the exhaust bridge on the inside of the cylinder bore. The exhaust bridge is the edge of the wall separating the exhaust ports on some 2 stroke cylinders. Why do I need to relieve the exhaust bridge? Now that we know what the exhaust bridge is, it’s important to understand why we feel this machine work is essential to replacing a 2-stroke top end. The most heat in your motor is generated from combustion in the cylinder during normal operation. Specifically, the exhaust port(s) of the cylinder are exposed to the most heat because this is the only way out for the hot gas produced during combustion. This means that under normal running conditions, your piston and your exhaust bridge are constantly under the pressure of extreme heat. Wiseco pistons are made from forged aluminum, which offers more strength and reliability, but also expands faster under heat than an OEM cast piston. The exhaust bridge will also expand more than the rest of the cylinder because it is such a thin structure. The lack of material makes it harder for heat to dissipate before it affects the aluminum and causes expansion. Expansion under heat is normal, but must be compensated for to make sure you get the most life and best performance out of your top end. Relieving the exhaust bridge simply means taking a small amount of material off the face the bridge in order to make room for expansion. If there wasn't any extra clearance, the exhaust bridge would expand past the cylinder wall once your motor heats up. This leads to scoring on the piston as it comes into contact with the exhaust bridge, especially as the piston expands at the same time. Notice the small amount of material taken off of the exhaust bridge, and the blending back into the cylinder. Read below on how to accomplish this. Relieving the Exhaust Bridge Now that we have some understanding established, let’s go through how to get it done. As always, if you don’t feel comfortable doing this work, this can commonly be done by the shop performing your cylinder work. If you have the rights tools, this can be done in the garage on cast iron and steel cylinder bore liners. We recommend using a die grinder with a small sanding roll to gently remove .003” of material off the cylinder wall face of the exhaust bridge. After the material is removed, the machining must be blended with the rest of the cylinder wall at the top and bottom of the exhaust bridge. You want to make sure there’s an easy slope for the piston ring to slide over when entering and exiting the exhaust bridge relief. If your cylinder is lined with Nikasil, this process will not work because that material is too hard. Your exhaust bridge must be relieved before being lined with Nikasil to achieve the same result. Check with the shop you choose for your cylinder work if you are unsure. Why do I need to drill holes in my piston? Relieving the exhaust bridge will make sure there’s no expansion past the cylinder wall, but we still want to make sure we keep the heat as low as possible. With small holes drilled into the skirt of the piston, oil underneath the piston will makes its way through the holes, and lubricate the contact point between the piston and exhaust bridge. Better lubrication means less friction, and less friction means less heat, which is what we want to make sure we don’t have any abnormal wear. Drilling Lubrication Holes Make sure you have the instruction sheet that came with your new piston. This drilling information can also be found there, complete with a visual diagram. Be prepared with your instruction sheet. 1. Install the piston and wrist pin on the connecting rod with one circlip. Make sure the arrow stamped on the dome of the piston is facing the exhaust side of the cylinder. 2. Slide the cylinder over the piston until the cylinder is in its normal position on the crankcase. Temporarily install the piston on the connecting rod and slide the cylinder over the piston. 3. Slowly turn the engine over until the bottom ring groove (or the only ring groove if your piston has only one) on the piston is at the top of the exhaust bridge. You can look through the exhaust port of the cylinder to help know when the piston is in the correct spot. 4. Go through the exhaust port with a pencil and trace a line on the piston skirt for each side of the exhaust bridge. Trace two lines on the piston, one on each side of the exhaust bridge. 5. Once the lines are traced and visible, remove the cylinder and the piston. 6. Start .300” below the bottom ring groove and mark two points .375” apart from each other. Make sure the points are centered horizontally between the two lines you traced. Use the proper measurements to mark 2 points for the holes to be drilled. 7. Drill two holes .060” - .090” in diameter (1/16” or 5/64” drill bit) on your marked points (one hole on each point). Drill holes on your marked points with one of the specified drill bits. 8. Remove all burrs from drilling the lubrication holes. On the inside of the piston, lightly sand with 400-600 grit sand paper. On the outside of the piston, use a ¼” drill bit and twirl it between your fingers over the holes you drilled to break away any edges and imperfections. 9. Wash the cylinder and piston with soap and water, and use compressed air to remove any water and debris. 10. Wipe the cylinder wall with light coat of oil. Whichever 2-cycle oil you normally use is fine. 11. Continue your top end rebuild as normal. This is how your final product should look all cleaned up and deburred. Why doesn't Wiseco pre-drill the holes in the pistons during manufacturing? Some Wiseco two-stroke pistons do come with these lubrication holes pre-drilled. However, there are certain applications that use the same piston across a wide range of model years, but the location of the exhaust ports across those years changes. Therefore, while the piston remains the same, the location of the lubrication holes will vary based the specific year cylinder for certain applications. Want to see the latest in 2-stroke piston technology? Read about the Wiseco 2-Stroke Racer Elite pistons here. See all that Wiseco has to offer for your 2-stroke here.
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