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Found 16 results

  1. I was checking on my piston not even 5 hours after rebuild and I came across this mess. Does anyone know how this could of happened?
  2. Rebuilding a top end is a task most two-stroke owners will run into at one point or another. Here, we go over critical steps and key tips to installing a new piston and ring(s) in your two-stroke. Periodically, if you own a two-stroke, there will come a point where you need to rebuild the top end of your engine. Hopefully, this won’t come as a surprise to you and will be part of your planned maintenance schedule versus experiencing an unplanned engine failure. While two-stroke engines are relatively simple mechanical devices, rebuilding them requires knowledge of how they work, attention to detail, and a systematic approach. We’re going to cover numerous tips pertinent to two-stroke top end rebuilds. These tips will be discussed chronologically and will encompass all phases of the build from pre-rebuild prep, to disassembly, through post build. The tips we’re going to share shouldn’t be considered inclusive of everything that has to be done, but are tips that focus on things that are either often overlooked or incredibly important. Let’s get started! Pre-Teardown Diagnosis - Before tearing the engine apart, are there any signs that a specific problem exists? If so, are there any diagnostic tests such as compression or crankcase leak down that are worth performing? Before tearing your engine down, asses the specific problem with you're engine if you're rebuilding due to a running problem. Clean Machine - Take time to thoroughly clean the machine before opening up the engine, especially if you will be servicing the top end without removing the engine from the machine. Service Manual - Performing engine maintenance without an OEM factory service manual is not recommended. Make sure you have a manual for your machine prior to starting work. The manual is the only place you’ll find service limits, torque specs, and other key data. Disassembly Limit Contaminants - Once the cylinder has been removed wrap a clean, lint-free rag around the top of the crankcase. Dirt is one of the leading causes of engine wear, and limiting the opportunity for dirt to enter the crankcase is very important. Keep a lint-free rag at the top of the crankcase at all times while it is open and exposed to potential contaminants. Piston Removal - Easy piston circlip removal can be accomplished by using a pick and needle nose pliers. Insert the pick into the dimple in the piston and behind the circlip. Then use it as a lever and pry the circlip out partially. Once out partially, grab the circlip with needle nose pliers. During this process, be careful not to scratch or mar the wrist pin bore as this will make removing the wrist pin much more difficult. Use tools as needed to aid in circlip removal, but be careful not to mar the pin bore so the wrist pin can be easily removed. The ease of pin removal will be largely dependent on the engine design and condition of the bore. If the pin can be removed by hand, great, if not, light tapping while supporting the rod is permissible. Otherwise, a pin puller should be utilized which can be bought or made. In its simplest form, this can consist of an appropriately sized bolt, nut, and socket. Once the wrist pin has been removed, the piston can be removed from the rod. Hopefully, the wrist pin can be removed by hand once the circlip is out. If not, an appropriately sized socket with some light tapping from the opposite end can help break it loose. Power Valve Disassembly - Prior to taking the power valve system apart, spend some time reviewing the procedure in your service manual. For additional insight into how the components interact, review the exploded views in the service manual and look at part microfiches, which can be found online. Online microfiches can be very helpful to double-check reassembly of the power valve. They can be found on many motorcycle dealer websites. When removing the power valve system, consider laying the components out on a clean rag in an orientation that correlates to how they are installed in the engine. This is a relatively simple thing to do that will help you remember how they are installed later. When it comes to cleaning the components, clean them one at a time or in small batches so that they don’t get mixed up. Lay out all the parts of your power valve assembly as you disassemble it. This will help you keep everything organized, and make sure you get it back together correctly. Inspection Reed Valve - Don’t forget to check the condition of the reed valve petals, cage, and any stopper plates. Most service manuals will detail the acceptable clearance between the petal tips and cage as well as the stopper plate height. Ensure any rubber coatings on the reed cage are in good condition. Inspect all reed valves components thoroughly before reassembling the top end. Any parts showing signs of excessive wear or damage should be replaced. Intake Manifold - Check the intake manifold for cracks. Cracks are more common on older engines, and propagation all the way through the manifold can lead to air leaks. Exhaust Flange - Check the condition of the exhaust flange and ensure that it is not excessively worn. An excessively worn flange will make exhaust gas sealing difficult, hamper performance, and leak the infamous spooge. Power Valve Components - Take a moment to review the condition of all the power valve components. Significant wear can occur over time and lead to performance losses. Rod Small End - Check the small end rod bore for surface defects such as pitting, scratches, and marring. Any severe defects in the bore will necessitate rod replacement. The rod small end is a critical point of inspection. Any damage to the inside surface could affect the small end bearing, leading to a chain of top end problems and potential failure. Sourcing New Components When freshening up the top end in your two-stroke, it’s important to reassemble with quality components. A deglazed and honed or bored and replated cylinder is a critical component to ensuring reliable performance from your new top end. Your local cylinder shop should be able to handle the bore and replate when necessary, and a simple deglazing can be accomplished with a Scotch-Brite pad. Be sure to retain the 45-degree honing mark angle. There are a lot of choices for new pistons from the aftermarket out there, but many people choose to stick to OEM. However, when ordering from the OEM, every individual part must be ordered separately, including the piston, ring, pin, clips, gaskets, etc. Dealing with all these part numbers and chancing forgetting a component can be a pain, and get expensive. ProX two-stroke pistons are manufactured by OEM suppliers, and come with the piston, pin, ring(s), and circlips all under one part number. ProX two-stroke pistons are manufactured by the same OEM-suppliers to exact OE specs. They are available in A, B, C, and D sizing for most applications. ProX pistons come with the piston, ring(s), pin, and clips all in one box. Complete top-end gasket kits can even be ordered under one part number. ProX pistons provide an OEM-replacement option with less hassle and less strain on your wallet. Find ProX pistons for your bike here. Even though ProX pistons are made by OE suppliers, the quality control difference is evident. On the left is a ProX piston for a Honda CR250, and on the right is a brand new piston out of the box from Honda. Which would you choose? Measurements The number of measurements that should be taken throughout the top end rebuild will be discretionary. At ProX, we strive for excellence and err on the side of caution when it comes to engine building, so our builds consist of numerous measurements and inspections prior to reassembly. For us, this ensures a high level of confidence and safeguards against external oversights. We recommend the same to anyone building an engine. Below is a list of measurements that we routinely make when rebuilding a two-stroke top end: Piston ring end gaps Piston-to-cylinder clearance Rod small end diameter Out of these measurements, confirming or adjusting the ring end gaps is by far the most important, followed closely by ensuring the cylinder bore is within spec with respect to diameter, straightness, and roundness. Understandably, some measurements may be difficult for the average home builder to execute, usually due to not having the right equipment, however, a competent shop should be able to assist. Ring end gaps can be checked by installing the ring in the bore without the piston, and using a feeler gauge to find the measurement. Correct ring end gap is listed in the installation instructions that come with a new ProX piston. ProX rings often do not need to be filed as they are pre-gapped, but it's always a good idea to make sure your end gap is within the provided spec. Piston-to-cylinder is another measurement that should be checked before final assembly. For this, use a bore guage and a set of calipers to measure the bore size. Next, grab a set of micrometers and measure the piston. ProX pistons should be measured perpendicular to the wrist pin, a quarter of the way up the piston skirt from the bottom. Subtract your piston size measurement from your bore size, and you have your piston-to-cylinder clearance. ProX pistons come with a chart on the instruction sheet that shows the range your clearance should be in. Measuring piston-to-cylinder clearance is a smart precaution to help ensure you won't run into any unexpected issues with your new top end. A final measurement we recommend taking is the rod small end diameter. This is important because sometimes these can get worn out and create free play for the small end bearing, resulting in damage to the bearing and most likely the entire top end. It can be done using the same method as the bore diameter. Compare your measurement to the acceptable range in your owner's manual. Making sure the diameter of the small end of the rod is within spec is often overlooked, but can prevent a serious top end failure. Prep Work Cylinder Cleaning - Once the cylinder has been deglazed or has come back from replating, it should be cleaned one final time. There is almost always leftover honing grit that will need to be removed. To effectively clean the cylinder, use warm soapy water and a bristle brush, followed by automatic transmission fluid or a similar cleaning solution and a brush or lint-free rag. To check the cleanliness of the cylinder, rub a cotton swab around the bore and look for contaminants. Clean the bore until no contaminants are visible on the cotton swab. Any honing grit that remains in the cylinder will facilitate premature wear of the piston rings. A clean, de-glazed, and properly honed cylinder is key to piston and ring function and longevity. Power Valve Function - Cylinders that have been exchanged or replated should have the power valve system reinstalled ahead of final installation. Often times, excess plating can inhibit power valve movement. To correct this, the excess plating must be carefully removed. On cylinders utilizing blade style power valves, the blade position with respect to the cylinder bore should be checked to ensure the blade does not protrude into the bore. Assemble the power valve before installing the new piston and reinstalling the cylinder. Be sure to check that the power valve is moving as it should, and not protruding into the bore. Piston - It is usually easiest to prepare the new piston as much as possible by installing one of the circlips and the ring pack ahead of joining it to the connecting rod. Unless your service manual dictates which circlip must be installed first, choose the easiest installation orientation. Typically, your dominant hand and preferred work orientation will dictate which side you choose to install the circlip on. It's easier to install one clip and the piston ring(s) before fixing the new piston to the connecting rod. Reference your service manual to determine the correct orientation of the circlip. Usually, the open end of the circlip should be oriented to the 12 or 6 o’clock position. Temporarily install the wrist pin and use it as a backstop so that the circlip is forced to move into its groove. Installing the circlip should be done by hand to limit the chance of deformation. Orient the circlip to the desired position, then push the open ends of the circlip into position first. Be careful not to scratch or mar the wrist pin bore in the process! Once installed, use a pick or screwdriver to confirm the circlip is fully seated and does not rotate. Any circlips that can be rotated must be replaced because they have been compromised and deformed during installation. Make sure to note the orientation of each clip after installation. Some manuals may recommend specific positions depending on the piston, but always be sure the gap is not lined up with or near the dimple(s). Rings - The compression ring(s) will be directional, and the top of the ring is typically denoted by markings near the end gaps. Apply a thin coat of oil to the ring, then carefully work the ring into position, making sure to line up the ring end gaps with the locating pin in each ring groove. Install the ring(s) with the marking(s) facing up, and make sure the ring end gap is lined up with the locating pin in the ring groove. Installation Piston - On the top of the piston, an arrow will be imprinted, which typically denotes the exhaust side of the piston. Consult your service manual to confirm the proper orientation of the arrow and piston. Apply a light amount of assembly lube to the small end bearing and wrist pin bore on the piston, then install the bearing. Align the piston with the small end of the rod, and slide the wrist pin into place. Once again, use the wrist pin as a backstop, then install the remaining circlip into position. Use a pick or screwdriver to confirm it is fully seated and does not rotate. Don't forget to apply some assembly lube to the ring and piston skirts before assembly! Cylinder to Piston - In most applications, a ring compressor is not required to compress the rings and install the piston into the cylinder. Lightly oil the cylinder bore with assembly lube or engine oil, then lube the piston skirt and ring faces. Prior to installing the piston and rings, confirm one final time that the piston ring ends are oriented correctly to their respective locating pins. Once the new piston is installed on the connecting rod, apply some assembly lube to the cylinder wall, and carefully slide the cylinder over the piston. Squeeze the ring with your hand as you slide the cylinder on, simultaneously making sure the ring end gap remains aligned with the locating pin. Position the piston at or near TDC then carefully lower the cylinder bore down onto the piston. Use your fingers to compress the ring(s) and ensure the cylinder bore is square to the piston. Feel how easily the cylinder slides over the piston and rings. The installation of the cylinder should be smooth and offer little resistance. If resistance is felt, stop immediately and assess the ring pack. Occasionally one of the rings may come out of position in its groove and snag the cylinder bore. This typically happens as the ring transitions out of your fingers and into the cylinder bore. Once the cylinder is safely over the ring, slide it all the way on keeping the piston at top dead center (TDC). Don't forget to torque your cylinder and head nuts to the specification listed in your manual. Post Build Torquing - Your cylinder and head nuts should always be torqued to the specifications outlined in your service manual. Double check all the nuts are set at their corresponding specs. Spark Plug - Don’t forget to install a new spark plug and if necessary gap it appropriately. Air Filter - Be sure to install a clean air filter prior to start up. Crankcase Leak Down Test - As one final precautionary measure perform a crankcase leak down test. A crankcase leak down test will help confirm all the seals, gaskets, and joints are sealing as they should. Break-In - When running your new top end for the first time, keep the engine slightly above idle, with slow and mild revs until the engine starts to get too hot to touch. Then, shut the engine off and let it cool until it is warm to the touch. Repeat this process, revving slightly higher and letting the engine get partially hotter each time. After 3 cycles like this, let the engine completely cool, then check all your fluids and re-check the torque on your cylinder and head bolts. Once that is squared away, you can begin break-in runs riding the bike. Make sure to keep the RPMs varied while riding for the first time, not letting the engine lug or sit at idle. A safe bet would be to ride the bike like this for 5 minutes, then 10 minutes, and finally 15 minutes, with adequate cooling in between. This will ensure your piston ring(s) are evenly and properly broken in. It’s never a bad idea to double check your fluids and torque one more time after complete cool down.
  3. 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.
  4. Evan Dodd

    Cast Piston durability

    I was looking at putting a Prox Piston in my kx 250 for my next rebuild. Have other things to get don't really want to buy a wiseco. How durable would it be in my bike, how long would it Last. I ride Michigan trails. Usually pretty tight averaging 30 mph. Also, ride Hatfield McCoy. Dont usually get on it hard besides the occasional drag race with friends. Would this Piston last a summer in my bike I will rebuild every summer anyway. Probably put 50-60 hours on it a summer maybe closer to 40.
  5. Hello all... First time here and I hope this is a good area to post this piston head question. I purchased this 2005 KX85 Kawasaki as it wasn't running from the seller, says he couldn't get it started and I've been doing maintenance to it as it was way over do as the carburetor was filthy and the jet were clogged, unclogged clean up carburetor and put back together. So I got around to check the valves from the carburetor side of the piston head looked very good then I removed the bikes pipe and took a photo of the piston head from that end and I noticed a scar or a gouge in the piston head , I really don't think that should look like that. Looking for feedback on what to do next as repait that piton head or can I try to start the bike even thought of this issue with the scar/gouge in the piston head? Any feedback would be helpful. ..
  6. 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!
  7. 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.
  8. Replaced the O-rings and bushing on my front forks of my 2000 Honda CR250R. Got to the step of adding fork oil and did all that but when I pump the piston rod to bleed out air I cant seem to get any pressure for the rod to go back down. It goes down about an inch then stops. Still hear sounds of air pressure in the system possibly but Ive pumped it about a hundred times. Manual says if you cant get pressure youve added too much fluid so ive adjusted it and still no progress. Any ideas on what may be wrong o
  9. yowaR

    Crf80 piston length

    Any one know the length on crf80 piston and what other piston y can used ? Dont worry about the piston pin i ca. Make sleeve for the pin
  10. Lightweightx

    KTM Pistology

    Recently just rebuild my 250 SX due to low compression. Slapped in a new forged Woessner and gotta break it in today. The old cast vertex really took a beating, it somehow looks like the bike is running too hot/lean? Main Jet is up a size already.
  11. Purchase any Wiseco Powersports product(s) with a subtotal of $250 or more between March 21st 2018 and May 31st 2018, and receive a ProX air filter FREE by mail-in rebate! Just follow the redemption process outlined below. A Race-Quality, Dual-Stage Air Filter for Free! ProX air filters feature dual-stage bonded foam, to capture dirt and debris, from coarse to fine. The thick, flat sealing ring provides a proper seat on the air box, to keep everything but air out. ProX air filters optimize air flow and protection in one package. How to Redeem Your Free ProX Air Filter: Purchase Wiseco Powersports product subtotaling $250 or more between March 21st 2018 and May 31st 2018. Download the rebate form here. Complete the form and include a copy of your receipt showing the seller's name/company and selling price(s), and the product serial number(s). Cut out the barcode label(s) on the side of the box with the Wiseco part number(s) and mail in with your redemption form. Mail completed form and copy of receipt to: Wiseco Performance Products Attn: ProX Air Filter Rebate 7201 Industrial Park Blvd. Mentor, Ohio 44060 You will receive your free air filter in 4-6 weeks. Go here for complete details and terms and conditions. ProX air filters feature dual-stage bonded foam and thick sealing rings, creating a reliable combination of protection and performance. Learn about proper air filter maintenance and performance here.
  12. 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.
  13. Hi, Im new to riding and planning to buy my first bike (a 125 2 stroke) and ride it in the mountains (image below) now i was wondering how long a piston will last in these conditions. i have no experience riding bikes so i thought someone here might have an idea, thanks for taking the time to read this
  14. protex1

    New parts again

    Rebuilt top end on our 2014 KX250F. C4MX head with all new parts. New Weisco HC Piston and Cylinder. Vortex X10 ecm. Web intake cam. FMF Mega Bomb header stock muffler no mid pipe. Raced one night ran fast but stumbled and sputtered under at low speed when giving full throttle. Took to dyno and tuned the ECM fuel settings via Air/Fuel ratio and the response is great from slow thru wide open. (this engine is on our outlaw kart on 1/8 mile dirt banked oval. 50+mph 10 sec laps. wide open at green rarely lifting.) second race after dyno runs the header starts to glow under warm up in pit but not when racing. engine began to make some noise. third race night engine is knocking loud and i am concerned, we ran it and it was quiet after it was hot. intake side of piston skirt is galled and scratched up. the cyl wall is galled up. the rest of piston is looks great. now i need another new P&C. can anyone confirm if this sounds like a bad lean condition?
  15. As the title suggests, I've been debating the idea of throwing in a high compression piston. It will bump the compression in my 2014 KTM 350 XC-F from 13.5:1 to 14:1. First and foremost my main question is, because I live under 1000 ft and usually run 97 octane REC gas, will I have to change the fuel I run or not? Also, will I have to change out the cams to aftermarket and re-time the whole motor and ignition? I guess I really don't know what to expect so any advice will definitely help! Attached below is a photo of the bike I plan on putting it in.
  16. Kevin from Wiseco

    Proper Motorcycle Engine Break-In After Rebuild

    Proper engine break-in is equally as important as a proper rebuild. Here, we'll go over a checklist to make your build will last, as well as a step-by-step break-in process. Putting in the time and money to rebuild your motorcycle engine is both a critical job and a prideful accomplishment. The feeling of an engine failure right after a rebuild is a sinking one, and will most likely stir up a mixture of frustration and disappointment. We want to help as many people as we can avoid that feeling. So, we've put together a review checklist for your rebuild, followed by a general engine break-in procedure, because your motorcycle should bring joy and fun to your life, not take tufts of hair out of your head. We'll start with a quick review on the motorcycle top end rebuild. Be sure these critical steps and precautions have been taken. If you find any concerning discrepancies, it's worth it to pull back apart and double check. Be sure that you have proper piston to cylinder clearance. Recently, a cylinder was bored with requested .0035” clearance. This machine shop has been in the area for over 30 years. When complete, it looked like it was tighter. He slipped the piston through the cylinder a few times and said, "It's okay." He was asked to check again, which he refused, and said that it was correct, and that he was too busy. Back in the Brew Bikes shop, it was double-checked, and clearance was .0015”. Yes, way too tight. Don’t just take someone’s word that clearance is correct, always double check it! Always double check your piston-to-wall clearance. Was the honing of the cylinder properly done? Honing is required to be done after boring, and if the cylinder was not bored, it still is needed to deglaze the cylinder for proper ring break-in. Different honing tools are better used for different applications, with common tools being brush hones and flex hones. Safe grits and hone materials depend on the cylinder finish, so check your manual or with the cylinder shop for a recommendation. Be sure that the crosshatch is at 45 degrees. The proper crosshatch will retain the proper amount of lubricating oil while allowing the rings and piston to break-in. Too little of crosshatch or too much will not allow the rings to break-in correctly and never get the proper sealing they were designed for. Read our full guide to cylinder prep. After proper honing and deglazing, your cylinder wall should have a consistent, 45 degree crosshatch. If the bike is a 2 stroke don’t forget to chamfer the ports. If it has a bridge in the exhaust port, most pistons require this area to be relieved. READ the piston specs, and if you don’t understand, be sure to reach out to Wiseco for specifications. Read our guide to relieving the exhaust bridge in 2-stroke cylinders. A critical step in 2-stroke cylinder prep is port edge relief and exhaust bridge relief. This will help ensure smooth piston and ring operation, and combat accelerated ring wear. Be certain that the ring gap is within specification. Don’t assume it is correct, check it. Always double check your ring end gap. With your compression ring in the cylinder, measure the end gap with a feeler gauge to ensure it's within the spec included in your piston instructions. Proper cleaning of the cylinder. Before you start cleaning make sure the gasket areas are clean with no residue of gasket or sealers. First, use a cleaning solvent with a brush and then again with a rag. This is not enough, and you will need to clean with dish soap and water. Using a clean rag you will be amazed on how much grit from the honing is still in the cylinder. Be sure to clean the piston also. Thoroughly cleaning your cylinder for a rebuild is critical. Be sure all old gasket material is removed, and use a 2-step cleaning process of solvent with a brush and rag, followed by soap and water. When the cylinder is clean and dry, you should be able to wipe the cylinder wall with a clean rag and not see any honing material residue. Then before assembly, use plenty of assembly lube on the cylinder and the piston. Don’t forget to lube the piston pin and bearing along with the rings. Assembly lube on the piston, rings, cylinder, pin, and bearing is important for proper break-in. Many rings have a topside for proper sealing. Double check this and be sure the proper ring is on the proper landing on the piston. Again, read the instructions that came with the piston. Piston ring markings vary, but the marking should always face up when installed on the piston. The gaskets and quality play an important part of engine rebuilding. If a gasket is thicker than the original, it could result in a loss of power. Worse yet, a gasket thinner than the original will result in less deck height (piston to head clearance). This reduced clearance may result the piston to come in contact of the head causing permanent damage. After placing the gaskets, be sure while assembling the piston in the cylinder that the ring gaps are in proper placement. Check your engine manual for proper placement of the piston gaps. Then, install the head. Many motorcycle manufacturers have a desired head nut tightening sequence. Refer to their procedures while doing this. Most companies give the head nut torque rating with the washers, nuts and studs being clean and dry. That means if you use oil or a thread locking compound the studs will be over-stressed due to the over-tightening of the head nuts. Engines have been damaged by this. Now you know, follow what the engine manufacturer recommends! Regardless of the type of motorcycle engine you're working on, there should be a tightening sequence and torque spec for the head nuts. Pay close attention to the specs in the manual, as these are critical to prevent damage and for proper operation. Use the proper engine oil and fill to the proper level. The fuel you use should be fresh and of the proper octane. If your engine is a 2 stroke, mix to the proper fuel/oil ratio. For just about any 2-stroke, whether vintage or a newer, a 32:1 fuel/oil mixture is very common, but check your manual for the recommended ratio. Not only is it important for piston lubrication, but also for the crank bearings and seals. After all this work has been done, and you feel confident with the rebuild, what else can go wrong? PROPER ENGINE BREAK-IN! So many mistakes can happen while breaking in the piston and rings, resulting in rings never properly sealing or/and piston galling. Many builders have their own procedures, but most all do heat cycling for breaking in engines. Before we get into it, please note that this is just one of many methods that work well for engine break-in. Many people have many different effective methods, this is just one example that has worked well for us. Use this break-in procedure as a guideline for your next fresh top end: It's important to ask yourself if the rebuilt engine is still using the same carburetor, air cleaner, exhaust system, cam, compression, or if a 2-stroke, the same port work configuration? Any changes can result in air/fuel mixtures to be either too rich or too lean, resulting in engine damage. If your engine is fuel injected and in good working order, the ECU and O2 sensor should keep the air/fuel mixture correct. If you have access to an air/fuel meter, or if a 2-stroke, an EGT (Exhaust Gas Temperature) gauge, check the air/fuel mixture. Even with these tools, spark plug readings are still recommended. Spark plug readings are a sure-fire way of knowing if your engine is running too lean or too rich. We'll get into more detail in a later article, but generally the plug will look white when it's too lean, and dark brown or black and wet when too rich. At first start up, keep the engine just above idle and give it a few revs up and down. This power on and power off RPM breaks in the piston and rings evenly on the intake and exhaust sides. If air cooled, once the engine builds up heat where it becomes too hot to touch, shut the engine off. If water-cooled, once the engine coolant starts rising in temperature, shut the engine off. This initial warm up takes just a couple minutes. Now wait a few minutes until the engine is slightly warm to the touch, repeat #2, letting the engine get slightly hotter. Be sure to keep the engine RPMs above normal idle and keep the RPMs going up and down slowly. Let it cool again till it is slightly warm to the touch. This time, start and run longer until the engine gets near operating temperature. If air cooled, be sure you have a fan pushing air from the front. You now can rev the RPMs up a little higher, being sure not to hold it at a sustained RPM, but revving it up and down. Let the engine cool completely. Check all fluid levels to be sure there is no loss of engine lubricant, or, if water-cooled, engine coolant. After engine is cool, do a plug reading to be sure it is not running lean. Because the engine has run a few heat cycles, the gaskets may have compressed. It is VERY IMPORTANT to be sure engine is totally cooled down, and then check the torque of the cylinder head nuts. Most times the cycling head nuts will need some re-tightening. DON’T over-tighten; just tighten to manufacturers’ specification as you did when assembling the engine. Next, warm up the engine for a couple minutes as you did in the other procedures. Ride the bike, revving the engine up to normal riding RPM. Be sure NOT to keep the RPM too low and don’t lug the engine. These low RPM’s actually puts much more stress on the engine parts. If this is a dirt bike, running on a track is best due to the up and down RPMs the engine will experience. Don’t be afraid to run it normally. If this is a road bike, a curvy road is best due to the RPMs going up and down, this is a must! Don’t lug the engine and don’t go on an open highway that keeps the engine at a sustained RPM. This first initial ride will only be about 5 minutes. Let the engine cool till you can touch the engine. Follow the same procedure as above, but this time running for 10 minutes. This will be your last break-in run. Follow the above procedure and run for 15 minutes. Now is the time to let the engine totally cool down again. Check the fluids as you did before after the engine has completely cooled down, and do another spark plug reading. It is now time to do another check of the cylinder head nuts for proper torque. Sometimes no additional tightening is needed, but don’t be alarmed if you need to, because this is normal Check all your fluids once more after the engine cools, inclduing coolant and oil level. At this time, the rings and piston should be broken in. Go out and ride it. The first few times, just be sure not to get the engine overheated, but your ride times are not restricted. It never hurts to do another spark plug reading and double-check the head nuts after your first long ride. Enjoy your rides, and be safe!
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