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Piston ring technology has gone through a renaissance in the past 15 years. The age of the modern four-stroke ushered in the necessity for durable, highly powered machines. It only makes sense that piston rings were one of the first areas of interest. These days, powersports enthusiasts are blessed with an array of options built using space-age materials and coatings, unique geometries, and remarkable sealing technology. Here, we break down the newest advancements in four-stroke piston rings, and how these technologies can benefit engine builders and motorcycle riders alike. Three-Ring Piston Designs 4-stroke pistons apply to a variety of different engine types in powersports, and many of them use 3-ring designs. Most four-stroke pistons use a three-piston ring design for effective compression sealing and oil control. The top ring serves as the compression seal. The uppermost ring’s job is to keep the combustion gases from getting past, effectively sealing the piston for maximum pressure. The second ring is responsible for catching any oil that may be on the cylinder wall. It helps scrape oil down to the third ring, which is a baffle ring that collects all of the oil. The bottom ring guides the oil through holes in the piston and down into the bottom end. “You don’t want the oil going up, just as you don’t want compression going down. You have to seal in both directions,” states Wiseco's engineering representative. The third ring is the oil ring assembly, which is made up of the baffle-style ring that collects oil, and two thinner rings that sandwich the baffle ring, and help keep it uniform in the ring groove. There’s also a very detailed geometrical design for every ring in a three-ring piston layout. The top ring typically has a gentle barrel face so that the ring contacts the cylinder wall in a very narrow path. This shape lessens the amount of friction, while still effectively sealing the compression. Conversely, the second ring has an angular face. The job of the top ring (lighter, machined color) is to seal compression, which is why it has a barrel-shaped edge face. “Picture a jagged edge, where the sharp side is on the bottom. As it’s traveling downward along the cylinder wall it’s scraping oil, just like a windshield wiper as it’s going down,” mentions Wiseco's engineer. The second ring's job is to scrape oil as the piston travels downward. It has a jagged notch cut on the bottom of the ring to increase oil-scraping efficiency. Two-Ring Pistons Honda has long marched to the beat of a different drummer. It makes sense that the Japanese manufacturer wanted to go their own way when they introduced the CRF450R in 2002. The single-camshaft layout, known in marketing speak as “Unicam,” received most of the attention; however, Honda’s engineers also developed a unique two-ring piston design. By eliminating the middle ring in a traditional three-ring piston, the goal was to limit friction in the assembly and shorten the piston height. The latter benefit being a reduction in overall engine weight (the CRF450R was the lightest 450 four-stroke in its time). The top ring sealed compression and act as an oil scraping ring. The second ring collected the oil and sent it back into the bottom end. Honda was able to use a two-ring piston by developing technologies with the top ring that had, and continue to have, really unique geometries. Honda’s top ring seals compression and is also able to scrape oil on the down stroke. This was accomplished by putting positive twist on the piston ring. Two-ring designs in four-stroke pistons are still very relevant, mostly in racing applications, such as with the Wiseco Racer Elite pistons you see here. They allow for less friction and weight, but require advanced ring technology. Wiseco's engineer explains, “If the ring was sitting flat on a table, the outward edges of the ring would actually be upward. The ring isn’t technically flat, but instead cone shaped. As the piston heads upward toward compression, the ring is tilted upward and is sealing. When the compression event happens, the ring flattens out and seals solidly against the piston ring groove and cylinder wall.” Once the piston travels downward, the lower ring starts to twist upward again, which brings the bottom edge of the ring out against the cylinder wall to scrape oil. The ring is effectively doing two jobs. Notice the bevel cut into the inner edge of the ring. This gives Wiseco rings positive twist geometry, meaning it can tilt and flatten inside the piston ring groove to accomplish compression sealing and oil scraping with one ring. Advancements in Materials Piston rings are not exempt from a continued focus on utilizing space-age materials for bolstering performance. Truth be told, rings were manufactured out of relatively simple materials 25 years ago. They were either built out of cast-iron or alloy steel with a moly- or chrome-faced channel where they contacted the cylinder wall. A lot of these new ring technologies are alloy steel, with a caveat. Rather than putting chrome faces on the ring, ring manufacturers actually harden the ring through a process called gas nitriding. “Gas nitriding is a process of introducing hydrogen to the surface, which hardens the steel,” notes Wiseco's engineer. “That makes the ring more durable, and results in better wear against the cylinder wall. The harder surface works extremely well against Nikasil cylinder bores.” Gas Nitriding rings hardens the material, increasing durability against today's extremely hard-surfaced Nikasil cylinder walls. Nickel silicon is an extremely hard surface. In order for the piston ring to properly seal against the cylinder wall, it, too, needs to have a very hard surface. The focus has been on making rings that are harder every year so they have better wear properties, and seal better against the cylinder wall. Low-Tension Technology Piston ring manufacturers have had to adapt to new-age cylinder designs, which have a tendency to distort. That’s due to motorcycle manufacturers constantly looking for ways to decrease engine weight. One way to do that is by casting the cylinders thinner and thinner. As a result, the cylinder doesn’t typically remain round or straight. This creates an issue where the piston ring becomes unseated. The solution is in using low tension rings. This technology allows the ring to conform to uneven surfaces. In essence, the ring is able to follow the undulations of the cylinder wall as it’s twisting and turning during the stroke of the piston. Ring Land Design Closely inspect the second ring land, which is below the top ring and above the oil ring. Notice a cut channel, which has a jagged shape that resembles a triangle. Flat on top and tapering off at the bottom, the unique shape helps assist in gathering oil as the piston is on the down stroke. This is called an accumulator groove. It acts like a piston ring that gathers oil and drives it down into the bottom end. One some pistons, you'll find a channel cut into the second ring land. This is not a ring groove. This is the accumulator groove, which collects oil and returns it to the bottom end. “Ring land design is extremely important in these new four-stroke engines that only use two piston rings,” states Wiseco's engineer. “You’re trying to take weight out and make things shorter and lighter. How do you do the work of three rings with only using two rings?” The answer can be found in the shape of the ring land. This scientific design helps control oil and makes sure that it doesn’t travel up past the piston and into combustion. Anyone that has a lot of hours on their piston and rings will be able to physically see that they have a problem when they fire their bike up in the morning and little puffs of blue smoke come out of the muffler. That’s due to the parts wearing out and oil getting into the combustion area of the engine. Lapped Rings Take a ride in the Mr. Peabody’s WABAC machine to the late 1990s, when automobile companies discovered that piston ring manufacturers couldn’t make a ring flat enough that was necessary for ultimate sealing. They relied on placing rings on a surface plate and grinding them down in order to remove any high points or imperfections to the surface. This process created a better seal against the ring groove. Known as lapping, the technology became popular in NASCAR and Pro Stock Drag Racing, where ultimate ring seal yields horsepower gains. The lapping process takes a production piston ring and turns it into something better. This technology is now available in the high-performance world of motorcycles. “Roughly a year ago, Wiseco introduced the Racer Elite piston kits. One of the features we have included is a lapped compression ring,” explains Wiseco's engineer. “It immediately provides better ring seal, so you don’t need any piston break-in period. Normally, the rings will need to seed themselves to the piston over time. We’ve eliminated that by having the ring lapped to the ring groove. It’s a very precise fit, and you get a really strong ring seal. In turn, horsepower is improved.” Lapped compression rings were a recent introduction to powersports with Wiseco's Racer Elite. It achieves ultra-flatness, creating a better ring seal, translating to more compression and more power. Wiseco was so impressed by the performance increase of lapped piston rings, they brought the technology in-house. Find out more about how well ring lapping technology improves performance. Wiseco's engineer states, “We have the capability to lap just about any piston ring to optimize the surface. We knew that we needed to do it all under our roof and sell it to the market. It’s interesting, because the Powersports market doesn’t know much about lapped piston rings. At the same time, it’s almost an everyday thing on the automotive side.” The benefits of a lapped ring are immediately noticeable. Performance gains, reduced blow-by, and the lack of break-in period put the Racer Elite piston kit front and center in the high-end, premium race parts category. Gas Porting Gas Porting is a technique where tiny holes are drilled into the top of the piston that intersect the top of the ring groove. The technology forces combustion gases down through the holes and pushes the ring out against the cylinder wall. It’s a technique used to achieve ultimate ring seal, but it’s not meant for longevity. That’s because gas porting forces things to work against one another, resulting in the ring and piston to wear out faster. Gas porting is normally reserved for high-end applications, such as Drag Racing, because it bolsters performance (at the expense of a shortened lifespan). Gas ports are tiny holes that allow combustion gases in through the top of the piston and out inside the compression ring groove. This forces the ring out against the cylinder wall, improving the seal.
With years of performance piston experience, JE knows ring operation is just as important as piston quality. Follow along with our complete guide to installing rings on your motorcycle piston(s). The correct installation of the piston rings is an essential aspect of rebuilding any four-stroke engine. This task is perceived by many to be simple. However, there are vital aspects of ring installation that should not be overlooked. Improper installation of the piston rings can result in limited engine life, reduced power, and high oil consumption. In this article, we’ll walk step-by-step through the ring installation process so that the next time you’re rebuilding your engine, you know exactly what to do and what to watch out for. JE now has pistons available for many late model applications. Find the performance you've been looking for. For starters, never attempt ring installation without the appropriate documentation available for reference. At JE Pistons, comprehensive instructions are included with most new piston kits. This ensures the engine builder has the necessary information available to do the job successfully. The machine’s factory service manual should also be on hand throughout the build so that things like torque specs, service limits, and procedures can be referenced. It's important to read and understand any assembly and installation instructions that come with your pistons. These instructions are for representational purposes only and not valid for all JE pistons. Process Overview Before diving into installation details, a quick recap of the process will be helpful to understand what’s to come. Shown below is an outline of the major steps you’ll go through. Measure ring end gap Clean all rings Mark piston where the end gaps should align Install oil rings Install 2nd compression ring Install primary compression ring Verify groove clearance Not sure which piston ring set you need to order? Check out our guide here. In addition to understanding the steps you'll be performing, laying out all the components needed helps stay organized and prepared. Time for a new piston kit? Find one here! Step-by-step Process Measure Ring End Gap Before installing the rings onto the piston, it is imperative that the ring end gaps are checked and verified against the specs provided with the installation instructions or factory service manual, whichever is applicable. If more than one compression ring is used, confirm any design differences between the two by referencing the installation instructions. Chamfers on the inside edge of the ring or different markings at the ring ends are common identifiers used to denote ring differences. Need clarification on all the markings used on JE rings and pistons? Click here. To check the ring end gap, simply install the appropriate ring into the cylinder bore and position it near the top of the bore. Use the depth rod end of a caliper to ensure the ring is square to the bore. Next, use feeler gauges to measure the ring’s end gap. Carefully insert various thickness feeler gauges between the ring ends until the gauge just begins to drag between the ring ends. Note the thickness of the gauge and compare it to the end gap specifications provided. This process can be repeated for any additional compression rings used. The majority of JE's motorcycle rings are pre-gapped, but it's always good practice to check ring end gap for all compression rings prior to installing on the piston. At JE Pistons, the ring end gaps are preset at the factory to fall within spec when installed in healthy cylinders used for normal applications. The end gap of the first compression ring should always be less than that of the second compression ring. If the end gap specs are outside of range, first double check your measurements and verify the cylinder bore is the correct diameter. Assuming no issues are found with the measurements or cylinder bore and the end gap measured is too tight, the rings can be carefully filed. To do so, use a small file and file one end of the ring. Be sure to maintain parallelism to the other ring end as you remove material. Remove small amounts of material and check the end gap periodically so that you don’t remove too much material. If ring end gap does need to be adjusted, evenly file one end of the ring only in small increments and continue to check until it's at the desired spec. Clean All piston rings should be cleaned before being assembled onto the piston. Before cleaning, confirm the ring ends are free of burrs. Any burrs present can carefully be dressed by gently breaking the edge with a small file. Next, use your preferred parts cleaner to wipe down the rings and piston. Make sure your rings are clean and free of any debris or burrs. Mark the Piston Review the instructions provided with your piston kit, or the guidelines provided in your owners manual if no alternate instructions are provided, and note the specified positions of the ring end gaps. Use a marker to mark the edge of the piston crown with the intended ring end positions for the oil control and compression rings. Doing so will help ensure no orientation mistakes are made upon ring installation. Follow the ring end gap orientation instructions for your specific piston(s) and mark the piston so you know where each end gap should end up. Oil Control Ring Installation Modern oil control rings typically utilize a three-piece design and consist of two side rails and an expander ring. Three-piece oil rings can be challenging to install if the ring design and methodology are not understood. The expander ring is the waffle shaped ring and features a stepped edge on the top and bottom of the ring. The side rails are the two small, thin rings which complement the expander. When properly installed, the side rails sit on the top and bottom of the expander ring against its stepped edges. For this reason, the expander ring must be installed first. The other feature of the expander ring worth paying attention to is its ends. Due to the expander’s accordion-like shape, it is possible for the ring ends to overlap in the ring groove. For proper installation, it is imperative that the expander’s ends butt and do not overlap. The ends of the expander ring should be touching, but not overlapping. To install the expander ring, lightly coat it with engine oil. The expander ring is non-directional, so it can be installed in any orientation. Carefully work the ring past the compression ring groove into the oil ring groove. Adjust the expander ring as necessary, so the ring ends are correctly positioned. Ensure the ring ends butt together and don’t overlap. Start by installing the expander ring after lightly coating with oil. The side rails are also non-directional. Lightly lube the side rails then install them on the piston. Make sure the side rails sit correctly against the stepped edge of the expander ring and that their end gaps are positioned properly. Once the side rails have been installed, double-check the end gap positions of all three rings that comprise the oil control ring assembly. Ensure the expander ring’s ends are not overlapped and ensure the assembly moves freely within the oil ring groove. Oil and install the oil expander rails below and above the expander. Be sure they are resting evenly and the end gaps are lined up with the appropriate markings. Compression Ring Installation If the piston utilizes two compression rings, the second compression ring should be installed first. Refer to the installation instructions to determine the proper orientation of the ring before installation. Typically, dots or letters will be marked near the ring end, which denotes the top of the ring. Internal edge features such as chamfers may also be used to identify the ring and its correct orientation. Lightly oil the ring and then carefully work it over the piston into its appropriate groove. Adjust the ring’s end gap position so that it aligns with the mark you made for it on the piston crown. Repeat this process for any remaining compression rings. Install the compression ring(s) in a similar fashion, lightly applying oil and carefully working the ring around the crown of the piston. Be careful not to twist or bend the ring out of shape as it could affect its ability to seal properly. Confirm Groove Clearance Once the compression rings have been installed, the ring-to-groove clearance should be checked. To do so, insert a feeler gauge between the ring and groove. The clearance can be identified by finding the feeler gauge that drags ever so slightly between the ring and groove. Note the groove clearance and compare it to the specification provided in the installation instructions or factory service manual. One of the final measurements to take after the rings have been installed is compression ring to groove clearance. Use a feeler gauge for this and find the size that has slight drag. Compare this spec to what's outlined in your instructions or owner's manual. At this point, ring installation onto the piston is complete, and subsequent steps can be taken to complete the engine build. While installing the piston rings onto the piston is a critical step in the build process, it can be performed by anyone when the proper steps are taken. The process simply requires the correct measurements are taken, cleanliness is ensured, and installation techniques are used. In search of a quality, performance forged piston for your bike? Click here to see what's available for your machine.