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Found 7 results

  1. Profile and ovality are two main characteristics of piston design. Here we'll take a look at why pistons are designed to not be perfectly round. When you look at a piston, it is easy to think that they are a perfectly round, cylindrical shape. After all, they go into a round hole (the cylinder!) So why shouldn’t they also be round? The fact is, the external shape of a piston is very sophisticated. An internal combustion engine is a hostile environment where combustion gasses can reach dangerous temperatures, and there could be port windows and surface undulations from uneven cylinder cooling. Designing a piston that is optimized for combustion chamber conditions is an important challenge. Throughout the years, piston materials and design characteristics to compensate for expansion under heat have evolved. Forging pistons out of aluminum provides great strength and durability, but it must be used in the correct design to properly optimize the performance of the piston. (Left) These are an example of early piston design, using steel as the primary material. These would not be sufficient for the requirements of modern engines. Compare with the variety of modern forged aluminum pistons from Wiseco (right) featuring different coatings and designs. Read more about the forging process here. There are two major characteristics of piston shapes: profile and ovality. Wiseco's Product Manager and long time engineer Dave Sulecki commented on these piston characteristics: “Piston profile and ovality are one of the most important features of a piston, these really determine not only how the piston will wear over time, but also how well the piston can perform. When the engineer calculates the piston to cylinder clearance, this is only the beginning of a complex determination of the final piston geometry." Profile If you roll a piston across a flat surface, you'll notice it does not roll in a straight line. You are observing characteristic number one: profile. Because aluminum conducts so much heat, pistons are designed with a taper -- the top of the piston, near the crown, is a smaller diameter than the bottom of the piston, near the skirt. The skirt of the piston actually is designed with what is called a barrel shape, illustrated below. This is beacuase temperatures near the dome of the piston vary from the temperatures at the skirt of the piston, resulting in different levels of expansion. The tapered shape allows the piston to expand as heat is applied, so the piston does not bind in the cylinder bore. The higher the temperature, the more the piston will expand. The design challenge then becomes calculating the degree of taper. Too tight of clearance can induce scuffing or seizure from heat expansion, while too loose of clearance can introduce noise from piston rock. This illustration shows piston profile: the barrel shape and taper pistons have. Because of this, measuring diameter on the skirts yields a larger number than measruing near the dome. "The piston profile is critical to how the piston will support itself as it reciprocates in the cylinder bore. For example, the piston profile must help hold the piston vertical in the bore during combustion; imagine any excess leaning of the piston would allow piston rings to become “unseated” and not seal properly against the cylinder wall," elaborates Sulecki. Ovality As you roll the piston across the table, you will also observe the piston rising and falling in a “hump-hump-hump” motion, much like a wheel that has a flat spot. This characteristic is called ovality, also known as camming. In the simplest terms, ovality means that the piston is smallest in line with the wrist pin bore. As the engine begins its movement, the connecting rod is not moving only up and down, but due to the rotation aspect is simultaneously moving sideways. This action from the connecting rod and the motion of the crankshaft place load forces on the piston along the plane of the connecting rod inline with rotation (known as the “thrust axis”). To allow the piston to move freely with this sidelong force, the piston cannot be perfectly round, or it would bind in the round cylinder bore. By applying ovality to the piston, the piston is free to move up and down as needed. The challenge in design is applying the proper amount of ovality. Too little ovality can cause the piston to contact the cylinder wall nearest the end of the piston pin, while too much ovality can cause the piston to ride too heavily against the cylinder wall along this “thrust axis.” Too much load along the thrust axis can result in heavy scuffing or seizure, when the piston breaks the oil film barrier and contacts the cylinder wall directly. This illustration shows piston ovality. The solid-lined ellipse represents the diameter of the piston as if you're looking down onto the dome. Dave Sulecki commented on ovality, "Ovality is an unknown thing, when most people look at a piston they think it is round, and to the naked eye this must be the case. However, take a new two stroke piston and roll it across the table and what happens? You will see the uneven “hump, hump, hump” as the piston rolls in a large arc…you are seeing both the profile (the “cone shape” of the piston”, in combination with the ovality as the piston rolls unevenly. Ovality is necessary for the piston to move up and down in the cylinder bore, as the crankshaft and connecting rod try to force the piston upward, and combustion forces the piston downward, ovality allows the piston to move without binding in the round cylinder bore." Your bike's engine need a complete rebuild? Or maybe just a piston and valves? Check out our Garage Buddy line of rebuild kits. Another visual representation of piston profile and ovality. Ovality is a key detail to remember when measuring piston size. The piston must be measured at the bottom of the skirt, 90 degrees from the wrist pin hole to reach an accurate measurement. When measuring piston diameter, be sure you’re using the proper tools. Do not use calipers to measure your piston(s), as you won’t get an accurate measurement. The most accurate tool to use is a set of outside diameter micrometers. Your piston should be measured at the bottom of the skirt, 90 degrees from the pin hole. Please note: The measurements displayed here are for representational purposes only. Measure each of your own individual parts for accuracy. Some Wiseco pistons feature proprietary skirt coatings such as ArmorGlide or ArmorFit, which are designed to reduce wear, provide smoother and quieter operation, and are applied to last for the life of the piston. With certain skirt coated pistons, piston-to-wall clearance measuring specs will change, so be sure to read the instructions that come with your piston(s). Click here to find out more about Wiseco's different coatings.
  2. Checking and adjusting valves is considered routine maintenance on high-performance four-stroke engines used throughout the powersports industry. Valve clearance inspections are not hard to perform and are well within the capability of most owners. However, there are tips and tricks that can make the job go smoother and yield better results. The JE Pistons team has been building and testing engines for over 70 years, and as a result, we know what it takes to do the job to a high standard. With years of experience in four-stroke engines of all types, JE is no stranger to the valve adjustments and maintenance. Whether you own a dirt bike, ATV, street bike, or any other four-stroke equipped machine, chances are your owner’s manual outlines when your engine’s valve clearances should be checked. Depending on the application, the inspection interval may vary from 15 hours to 15,000 miles. Checking clearances at the specified intervals is incredibly important to ensure the engine continues to run optimally and lasts a long time. Also, as a rule of thumb, anytime the top-end of the engine is disassembled, it is best practice to check valve clearances. Any time you have the top end apart to replace the piston, you should check your valve clearance and adjust as necessary. Before servicing your engine, you will need your machine’s factory service manual. The service manual is required because it specifies the required clearances, torque specs, and other information imperative to performing the task. The outline we’re providing should be considered supplemental to the information in your service manual and is in no way a comprehensive substitute. To tackle this job, you’ll typically need the following tools and supplies: Lash/feeler gauges Metric wrenches Metric sockets Clean rags or towels Screwdrivers Caliper In most cases, specialty tools aren’t utilized, however, if they are, you’ll find that information in your service manual. A critical tool to measuring valve clearance is a set of feeler gauges. Since the engine is going to be partially opened up and exposed, it is best to work on a clean machine. If your machine is dirty, take the time to clean it thoroughly so the risk of contaminating the engine with debris is lessened. Prioritize cleaning the cylinder head cover and surrounding area. Chances are you're not working on a new bike, so be sure the area around the cam cover is clean to avoid unwanted debris. We’ll begin outlining the procedure with the removal of the cylinder head cover. You’ll likely need to remove your seat, fuel tank and various other components before this. These items should be easy to remove, and your service manual should provide sufficient guidance. When removing the cylinder head cover, be extremely careful not to allow dirt to fall into the cylinder head. If you're working on an engine still in the bike, you'll need to remove your seat and tank, along with any other components hindering your access to the cam cover. Next, the valvetrain will need to be positioned so that the clearances can be checked. Most service manuals specify setting the valvetrain so that the piston is at top dead center (TDC) on the compression stroke. Setting the valvetrain at this position ensures that the cam, or cams, are on their base circles and that neither the intake or exhaust valves are open. The base circle of the cam is the circular portion of the cam which does not influence valve lift. As an aside and for future reference, while it is sensible to follow the service manuals recommendations on setting the piston position and engine stroke when the engine is assembled, it is not necessary, especially when working on an engine that is being rebuilt. Checking valve clearance can also be accomplished with the cylinder head removed from the engine and positioning the cam lobes opposite the lifter buckets to ensure the clearance measurements are taken with the cam on its base circle. Whether the head is still on the engine or you're working on it separately, be sure the engine is either at TDC or the cam lobes are resting somewhere on their base circle and not applying pressure to the buckets like they would when opening valves. Your service manual outlines the required procedure to set the engine on its compression stroke at TDC. Most engines have mating alignment marks on the crankshaft and engine case as well as the cam gear and cylinder head. It is imperative that you know and understand how to utilize these reference points because they are used to correctly set the cam timing after any valve clearance adjustments have been made. Once you’ve positioned the cams correctly, valve clearance measurements can be made using lash (feeler) gauges. Lash gauge measurements can be tricky due to surrounding geometry and inexperience on the user’s part. To obtain the most accurate measurement, it is essential that the lash gauge is inserted between the cam and lifter bucket as close to parallel as possible. To facilitate parallel entry, bend the lash gauges as necessary so that their tips can easily slide between the cam and lifter bucket. Measure valve clearance by inserting your lash gauge(s) between the cam lobe and lifter bucket. Accurate lash gauge measurements are subjective because they are based on feel. Ideally, the most accurate valve clearance measurements are obtained when the lash gauge passes between the cam and lifter bucket with a slight drag. Gauges that pass through easily or must be forced through should be considered too thin or too thick, respectively. When this occurs, other gauges should be tried, or, if you’re between sizes, the average of the two should be utilized as the valve clearance. Begin by the using the gauge equal to the median recommended valve clearance measurement in your manual. You may have to move up or down a couple sizes until you find the size that slides between the cam lobe and bucket with a slight drag. Record this measurement for each valve. After each of the intake and exhaust valve clearances has been recorded, they should be compared to the service specifications outlined in your service manual. If the valve clearances fall within the manufacturer’s recommended range, no further work is required. However, if the clearances are outside of the specifications, determining what adjustments need to be made is the next step. To do this, unless the current valve shim thicknesses are known, the cylinder head will have to be disassembled so that the shims can be removed and measured. Follow the necessary procedures outlined in your service manual to slacken the cam chain, remove the cam cap, cams, and lifter buckets. When removing the cam cap, be sure to follow any recommended removal/tensioning sequences. Once the cam chain is free, use a piece of wire to secure it to the cylinder head. If it happens to fall in the chaincase, a pen magnet can be used to fish it out. Be sure to slacken the cam chain before attempting removal. Remove the camshaft(s) and secure the cam chain so it doesn't fall in the cases. To remove the lifter buckets, a pen magnet or valve lapping tool are both excellent aids to utilize. When extracting the lifter buckets from their bores, be very careful and keep tabs on whether or not the valve shim sticks to the underside of the bucket. Oil underneath the lifter buckets makes sticking shims a common occurrence. Use a pen magnet or lapping tool to remove the buckets. Be careful of shims that may stick on the underside of buckets. Through engine operation, the lifter buckets mate to their respective bores so they should never be mixed around. To help keep track of things, draw out a simple cylinder head diagram on a piece of paper so that the lifter buckets and all the measurements can be tracked. Proceed to remove any remaining valve shims from the cylinder head. Once the valve shims have been removed, measure the shim thicknesses and the diameter of shims used. Drawing a simple diagram can help you keep track of what buckets and shims came from where. Once everything is removed, confirm your shim measurements. To determine what valve shim adjustments should be made, a simple formula is used: New Shim Thickness = Recorded Clearance - Specified Clearance + Old Shim Thickness Calculate the necessary new shim thicknesses for all the clearances that are out of spec. Valve shims are available from most OEMs, but helpful shim kits that come with an assortment of sizes are also available from the aftermarket. Before sourcing shims, you’ll need to determine the diameter of the shim you need because there are a handful of different shim diameters used within the industry. Shown below are the standard shim diameters. Size (mm) 7.48 (Japanese) 9.48 (Japanese) 8.90 (KTM) 10.00 (KTM) Shim assortment kits are available from various aftermarket suppliers, just be sure you know what shim diameter your machine takes before ordering. This kit was sourced from ProX Racing Parts. When calculating what new shim thicknesses are required, it is best to target the specified clearance on the upper end of the prescribed clearance range. This is advised because valve clearances usually diminish over time. Valve shims are available in 0.025mm increments, so the shims that can be utilized will also influence the new clearances that can be achieved. Once you have the correct shims in hand, the valvetrain can be reassembled. Use engine oil to lubricate the valve shims and carefully install them. The lifter buckets should also be lubed before installation. When inserting the lifter buckets into their respective bores, ensure that the buckets bottom on the shims and at no point comes back up. If the bucket comes back up upon installation, occasionally the shim will stick to it and become displaced. The engine can quickly be severely damaged if the shim is not seated correctly between the valve stem and lifter bucket. Using engine oil and assembly lube when reassembling your shims, buckets, and cams helps prevent premature wear and also helps your shims stay in place while re-inserting buckets. Pay close attention to your service manual during installation of the cams and when setting cam timing. Double check that the crankshaft is in its correct position. If you’re working on a twin cam engine, it is best to install the camshaft that resides opposite of the chain tensioner first (typically the exhaust cam), pull the chain taught from the crankshaft, orient the cam gear correctly, and then wrap the chain around the gear. Once this is accomplished, the remaining cam can be oriented correctly and the chain wrapped around it. Double check orientation of all components and that timing has been set correctly. Be sure to use engine oil to lube the cam bearing bores upon installation. Make sure your timing marks on your crankshaft are lined up, then reinstall your cam(s). It's important to make sure the timing marks on the crankshaft and cam(s) remain lined up simultaneously when reinstalling the cam chain. Click here for a more in-depth guide to setting cam timing. When installing the cam cap, ensure the torque specs and sequences outlined in your service manual are followed. Deviations from either can cause the cam bearings to wear prematurely. Once the cams have been secured, use lash gauges to confirm the new valve clearances match the clearances that were calculated. Any deviations that are found should be carefully scrutinized because they may be indicative of calculation errors or shims that are not seated correctly. If there is a hint of a problem at this point, it is imperative that it is thoroughly understood and corrected before proceeding. Be sure to follow the correct torque sequence and specifications when re-installing cam caps. Assuming everything checks out, the cam chain can be tensioned. Follow the procedure outlined in your service manual to do so. Once the tension has been set, rotate the engine through at least four complete revolutions. Doing so will help the automatic chain tensioners to set the correct initial tension and confirm that the engine has been timed correctly. Position the piston at TDC on the compression stroke and check that all timing features on the crank and cams remain in their specified positions. Complete the job by carefully reinstalling the cylinder head cover, making sure to torque those bolts in a star sequence to recommended specs. Once the rest of the machine is buttoned up, it’s time to get back to riding! More Tech Articles from JE Pistons
  3. Wiseco's new Garage Buddy engine rebuild kits offer everything you need for a bottom and top end rebuild. From the crank to the piston kit, and even an hour meter to track maintenance, everything is included in one box. Here we take a look at the components included, and the technology behind them. So, the time has come for an engine rebuild. Hopefully it’s being done as a practice of proper maintenance, but for many it will be because of an engine failure. Whether the bottom end, top end, or both went out, the first step is to disassemble and inspect. After determining any damage done to engine cases or the cylinder, and arranging for those to be repaired/replaced, you’re faced with choosing what internal engine components to buy, where to get them, and how much the costs are going to add up. A full engine rebuild is a serious job and requires a lot of parts to be replaced, especially in four-strokes. You have to think of bottom end bearings and seals, a crankshaft assembly, piston, rings, clips, wristpin, and the plethora of gaskets required for reassembly. If you’re doing this rebuild yourself, or having your local shop do the labor, chances are you don’t have a factory team budget to spend on parts. However, you know you want high-quality and durable parts, because you don’t want to find yourself doing this again anytime soon. Rebuilding a dirt bike engine is an involved job, requiring many parts to be replaced. Missing one seal or gasket can put the whole rebuild on hold. You could source all the different parts you need from different vendors to find the best combination of quality and affordability. But, it can get frustrating when 6 different packages are coming from 6 different vendors at different times, and each one relies on the next for you to complete your rebuild. Wiseco is one of the manufacturers that has been offering top end kits (including piston, rings, clips, gaskets, and seals) all in one box, under one part number for many years. Complete bottom end rebuild kits are also available from Wiseco, with all necessary parts under one part number. So, it seemed like a no brainer to combine the top and bottom end kits, and throw in a couple extra goodies to make your complete engine rebuild in your garage as hassle free as possible. Top-end piston kits and bottom-end kits come together to create Wiseco Garage Buddy rebuild kits. Wiseco Garage Buddy kits are exactly as the name implies, the buddy you want to have in your garage that has everything ready to go for your engine rebuild. Garage Buddy engine rebuild kits come with all parts needed to rebuild the bottom and top end, plus an hour meter—with a Garage Buddy specific decal—to track critical maintenance intervals and identify your rebuild as a Garage Buddy rebuild. The kits include: Crankshaft assembly OEM quality main bearings All engine gaskets, seals, and O-rings Wiseco standard series forged piston kit (piston, ring(s), pin, clips) Small end bearing (for two-strokes) Cam chain (for four-strokes) Hour meter with mounting bracket and hour meter decal Open up a Garage Buddy kit, and you'll find all the components you need to rebuild your bottom and top end. 2-stroke and 4-stroke Whether your machine of choice is a 2-stroke or a 4-stroke, Wiseco can help you with your rebuild. 2-stroke Wiseco Garage Buddy kits include everything listed above, featuring a Wiseco forged Pro-Lite piston kit. You don’t even have to worry about sourcing a small-end bearing, that’s included too. 2-stroke fans often brag about the ability to rebuild their bikes so much cheaper than their 4-stroke counterparts, and they’ll have even more ammo for bragging now with these kits starting in the $400 range. A Wiseco 2-stroke Garage Buddy kit includes all the parts you'll need for piston and crankshaft replacement, plus an hour meter to track your next maintenance intervals. However, don’t abandon your 4-stroke yet. Many riders cringe—and rightfully so—at the thought of rebuilding their 4-stroke because of the costs associated, but Wiseco 4-stroke Garage Buddy kits starting in the $600s takes a lot of sting off your rebuild project. They even include a new timing chain. No matter what you’re rebuilding, you’ll be able to track key maintenance intervals for your fresh engine with the Wiseco hour meter and log book that’s included in the Garage Buddy kits. All Garage Buddy kits include a specific hour meter decal as well, which is important for the limited warranty to identify the rebuild as a Garage Buddy rebuild. A Wiseco 4-stroke Garage Buddy kit includes all the parts you'll need for piston and crankshaft replacement, including a cam chain and an hour meter. Ease of ordering Wiseco Garage Buddy kits come with the listed parts boxed up in one box, and listed under one part number, which makes it nice to not have to worry about if you might’ve missed something when ordering. Simply find the single part number for your model, order, and you’re on your way to brand new performance. Quality Performance, backed by a Limited Warranty Ordering convenience doesn’t make a difference if the parts do not provide quality and reliability. Wiseco crankshafts are designed completely by in-house engineers, who determine all assembled dimensions, clearances, materials, and specifications. These specifications have been determined from R&D tests such as hand inspection, dyno, and failure analysis. Once Wiseco cranks have been manufactured to exact specifications they are batch inspected, and critical tolerances and dimensions are measured. Major inspections and tests include crank run-out and trueness, because they must operate within a strict tolerance to last long and perform well. Wiseco crankshafts and bearings are manufactured and tested according to strict tolerances and clearances, including run-out and trueness. Crankshaft designs are also tested for 4 hours at WOT. Bearings are another critical point of inspection. Wiseco has worked to build relationships with top-tier bearing suppliers to provide a long lasting, low-friction product. Debris in a bearing can lead to very fast wear, and Wiseco makes it a point to inspect batches of bearings for cleanliness and proper operation. As part of the design and engineering process, prototype crankshafts are hand inspected and dyno-tested at wide open throttle for 4 consecutive hours. This is a benchmark test, and new crankshaft designs must pass it before to be deemed worthy for manufacturing. Watch our crank R&D and inspection process. A Warranty on Engine Internals? Yes! Wiseco is committed to providing performance and reliability in all their products. This is why Garage Buddy kits come with a limited warranty. Rebuild your engine with a Garage Buddy kit, and your new Wiseco components are covered against manufacturer defects for 90 days from the date of purchase, or 10 hours logged on the hour meter, whichever comes first. Check out all the warranty details on the detail sheet in your new Garage Buddy kit. Open up your Garage Buddy kit and you'll find a detail sheet on the warranty on your new components. Forged Pistons The top end kits included in Garage Buddy kits feature a Wiseco forged piston, which are designed, forged, and machined completely in-house in the U.S.A. Four-stroke Garage Buddy kits come with a Wiseco standard forged piston, which offers stock compression and more reliability and longevity, thanks to the benefits of the forging process. Two-stroke Garage Buddy kits include a Wiseco Pro-Lite forged piston, which is the two-stroke piston that has been providing two-stroke riders quality and reliability for decades. Some applications, two and four-stroke, even feature ArmorGlide skirt coating, reducing friction and wear for the life of the piston. Forged aluminum has an undeniable advantage in strength over cast pistons, thanks to the high tensile strength qualities of aluminum with aligned grain flow. Read more about our forging process here, and get all the details on our coatings here. All Wiseco pistons are forged in-house from aluminum. Some pistons may also come with ArmorGlide skirt coating, and some 2-stroke pistons may already have exhaust bridge lubrication holes pre-drilled. All pistons are machined on state-of-the-art CNC machine equipment, then hand finished and inspected for quality. The forged pistons come complete with wrist pin, clips, and high-performance ring(s). Lastly, all gaskets and seals are made by OEM quality manufactures. Sealing components are not something to ever go cheap on, because no matter how high-quality your moving components are, if your engine is not sealing properly, it’s coming back apart. Need some tips on breaking in your fresh engine? Check this out. Gaskets and seals provided in Wiseco Garage Buddy kits are OEM quality, ensuring your freshly rebuilt engine is properly sealed.
  4. I just stumbled across a hell of a deal on a brand new FMF Megabomb for a 2014 KTM 350 SX-F. However, I have a 2014 KTM 350 XC-F, and on the ad it says the pipe fits the SX-F models but says nothing about fitting the XC-F. Does anyone know if the head pipes on the SX-F's and XC-F's are interchangeable? I assume they would be since they are identical motors, but I don't want to order it and be SOL.
  5. 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.
  6. 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.
  7. With a little bit of work on your part, Wiseco Garage Buddy Steel Valve Kits can help your dirt toys deliver years of service. Read on for full details on these reliable and affordable valve replacement kits. One of the basic truths of the imperfect world we live in is that the people who design machines are not the same people who have to maintain those machines. This often leads to situations where something that seemed like the way to go on the CAD screen turns out to be more difficult or more expensive to fix in the real world than it otherwise would be. Exotic materials and painstaking processes that are economical to implement when you’re mass-producing something turn out to be expensive to service in the field. Today's 4-strokes are engineered to be high-tech, but the parts come with a big price tag. In this single-serving, throw-it-away-when-it-breaks world, there are some noble souls who take a stand and say that we should be able to service and maintain things ourselves instead of discarding them, bringing new life to machines that need a bit of a refresh. Such is the case with Wiseco’s Garage Buddy Steel Valve Kits for a variety of popular dirt bike and ATV applications. Wiseco Garage Buddy Steel Valve Kits were engineered to be a more reliable and affordable option for riders who need to replace valves in their modern four-stroke machines. Read on for complete details! When faced with the price tag on factory replacement parts for bikes that came with trick valvetrain components, many owners cringe at the price of refurbishing a tired engine. However, with the right components at the right price, turning your dirt bike’s mid-life crisis around and letting it catch its second wind can be easy. Win on Sunday, Sell on Monday With the incredibly impressive machines under race tents worldwide, nobody wants to buy a new bike that has a whiff of “outdated” technology surrounding it, so a lot of the high-end features that really only make a difference to the top one percent of professional racers become must-haves for weekend warriors who just want to trail ride with their kids. When those parts wear out, the exotic bragging rights come with a cost, though. “Titanium is a great valve material due to the strength-to-weight ratio, and also the material’s ability to deal with the high temperature of combustion,” Wiseco Product Manager Dave Sulecki explains. “The light weight is important for engine acceleration; imagine how a heavy component takes more energy to move, and you can see where titanium is ideal when the camshaft needs to accelerate the valve quickly with less energy, and you can see that a lightweight component would be critical for a high-end racing engine.” Titanium is popular for valves for its light weight properties, but they are expensive to manufacture and can wear out faster than steel. While those race-spec valves come standard because they’re a positive selling point on the dealership floor, they’re mostly there for bragging rights instead of making a difference you’ll feel when twisting the throttle yourself, and it’s cheaper for the manufacturer to make everything to one specification than it is to have separate designs. “This light weight and performance comes at a greater cost,” Sulecki adds. “The material is more expensive, and costs more to machine or form into a valve. Additionally, the titanium requires a special coating to deal with the heat and wear, which also adds cost. This expense is needed for the highest performing engines, like the type you find in nearly all levels of racing from motocross up to Formula 1.” Sticker Shock Even expensive, exotic materials wear out, though, and when it’s time to freshen up the valvetrain of your bike, you might be surprised to see just how much it will cost to replace like-for-like with factory components. Per Sulecki, “Steel valves are a great low cost alternative to titanium, and offer longevity, reliability, and improved wear over titanium. Some customers are not always racing their vehicles, and just want longer service intervals and the peace of mind that comes with this material.” "Steel valves are a great low cost alternative to titanium, and offer longevity, reliability, and improved wear over titanium." - Dave Sulecki, Wiseco Powersports Product Manager That’s where Wiseco’s Garage Buddy Steel Valve Kits enter the picture. They’re designed to be an affordable way to refresh your high-tech dirt bike’s valvetrain. Although they may not be made from titanium, that doesn’t mean they aren’t precision-engineered. “Because steel valves are a small percentage heavier than titanium valves, heavier-rate valve springs are required to control the valve and protect the engine from valve float (the condition where the heavier valve will stay open under high RPM engine speeds),” Sulecki explains. “These springs are included with the Garage Buddy Steel Valve Kits.” Garage Buddy Steel Valve Kits are available separately for both intake and exhaust valves. They come complete with the valves, springs, and even a free packet of cam lube to make sure every box is checked during your reassembly. Converting to steel valves requires using valve springs designed for the specific weight of the valve. Springs are included with Garage Buddy Steel Valve Kits. Wiseco’s extensive experience with powersports valvetrain components provides confidence that their conversion kits are engineered to restore showroom-floor performance, and they utilize stock retainers, seals, shims, and other components for affordability and drop-in compatibility. The springs are crafted from premium chrome vanadium steel, and the nitrided steel valves can actually outlast an OEM titanium valve by a factor of three or more. Wiseco's nitrided steel valves are designed to utilize stock retainers, keepers, and seals. The steel conversion valve springs are manufactured from chrome vanadium steel. Time For A Change So, how do you know when it’s time to replace the stock components, short of a dropped valve or broken spring? Per Sulecki, “Valves and valve springs wear over time, like any highly-stressed engine component. When you are checking the valve clearance, or making shim adjustments, this is always a good indicator how quickly the valves are wearing or receding into the seat.” Keeping an eye on these telltales during your regular maintenance will allow you to judge when your factory valves and springs are reaching the end of their service life. Entire engine in need of a refresh? Garage Buddy also offers Complete Engine Rebuild Kits, check them out here. “When you are inspecting your top end for general overall health, such as the piston and ring condition, this is the best time to take a closer look at the valves and valve springs,” he continues. “Valves and springs need to be removed from the cylinder head for full inspection. Once these are removed, you can look closely at the condition of the valve face where it seals to the valve seat, and also the condition of the valve head overall and the stem condition. Any cupping or damage to the valve face means it is time to replace the valve, and any similar wear to the valve seat means replacement or re-cutting will be needed.” Inspecting your valves for wear while doing a top end is a good idea. Closely inspect the sealing surface of the valve for cupping, and inspect the rest of the valve for wear or damage. It's a good idea to also check the groove at the top of the stem for signs of wear to avoid breakage. Over time, springs become less elastic and may no longer be able to control valve motion at high speeds, but it’s not the sort of wear that is immediately obvious to the naked eye. Sulecki suggests, “Valve springs should be inspected for free length, and also overall condition, looking for any wear marks or defects that can lead to spring failure.” Any nicks or cracks are a sure sign of impending doom, and your cue to replace the entire set. Valve spring free length can be measured and compared to the recommended spec to get an idea of wear on the spring. Doing the Job Right Depending on your level of mechanical aptitude and how well-equipped your garage is, valve replacement might be a job you want to subcontract to a professional. “For most all valve replacements, it is a good idea to work with a qualified builder if you are not sure about the condition of any of these components,” Sulecki suggests. “The work can be done in your own workshop, but there are some special tools required to remove the valves from the head, and having an experienced eye on these items is always the best approach if you are not sure what to look for. An OEM service manual is always the best place to start, they will provide information about any special tools, and guidelines of what to look for regarding valves, valve seats, and even valve guides, and their condition.” When replacing your valves, be sure to use proper tools and follow all procedures and specifications outlined in your owner's manual. If you're unsure about performing your own valve maintenance, we recommend taking your machine to a trustworthy and certified shop. Whether tackling the job yourself or letting a pro handle your top-end maintenance, you’ll save time and money by seeing to all the wear-prone components at the same time. Sulecki adds, “When replacing valves, it is a good idea to inspect the top end for any concerning issues or conditions. Inspect the valve seals, valve keepers and seats, shim buckets, the condition of the cylinder head (flatness and sealing condition), and cam chain condition.” Needless to say, the time to service or replace these components is while everything is apart in the first place, and by using quality components like Wiseco’s Garage Buddy Steel Valve Kits, you’ll protect your investment for many off-road seasons to come. Wiseco Garage Buddy Steel Valve Kits are available separately for both intake and exhaust valves.
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