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so I'm wondering about buying a 250cc 2 stroke I just turned 15 and weigh about 120lbs and am looking for a dirtbike coming off a Yamaha banshee. I will be mostly riding in the sand dunes but do go up and ride semi technical trails and desert riding. i've heard that a 125 will not have enough power for sand riding. would I be able to hold the bike up being around 5'9-5'10? what would y'all recommend I look for. (not at all considering a 4 stroke because of the costs of rebuilds)
"While at Machu Picchu, one of the seven wonders of the world, Ryan was counting down the days for our dirtbike tour." Todd explained just moments before heading out on the trail. It's hard to look down upon the Andes as you fly into the Cusco valley, and not have your mind blown with the enormity and vastness of the terrain below the wings. If you are crazy passionate about dirtbikes, it's even more mind blowing to imagine riding it on two wheels. Todd and Ryan joined up with Scott Englund of MotoMission Peru for a custom three day hard enduro ride. The ride catered to their skill levels, journeyed across the type of terrain that the boys wanted to ride, and filled their minds with hundreds of unforgettable images of Peru. Each teetered on the edge of comfort as Scott managed to push them beyond their norms of riding in Colorado. The official tour video...Check it out! Toothbrush anyone? "There is something special about leading a father son duo into the back country." Englund said as he explained how his own father bred a bit of adventure in his own heart. "I get people from every corner of the planet. They are all awesome peeps, but to share this experience with Todd and Ryan, that's a thrill." Three days of exotic dirtbiking. Beginning at Englund's home, the trail begins just minutes from the garage. "No trailers, you'll see what I am talking about. You won't even have time to warm up before we hit the trail." Englund explained. What goes on inside of Motomission is nothing short of a dream. Scott has been running MotoMission Peru for a number of years. He is a social entrepreneur who gives 100% of the profits of the business to charity. His family is supported by a number of people and/or businesses who believe in his mission. Sponsors have supported MotoMission with equipment and gear. The marketing arm of the business are happy customers that tell others about the experience and share the included tour video via social media. Scott does what he loves to do. Riding dirtbikes, exploring new areas, cinematography, adventure, travel, serving others, business...It all fits his lifestyle. You can see it in his smile when he hands over the bike to you at the beginning of the tour. So many views! "I've got the coolest gig on the planet!" Englund states. "In my wildest of thoughts, I couldn't have dreamt up a better situation. I live here with my amazing family, all who ride, and I get to do what I love to do, while giving it all away." It's not all happy and easy. "It really sucks when you have to haul a bike out of a canyon in backpacks." recalled Englund of a time when a customer launched a bike off a ledge so steep and deep he couldn't see where the bike had landed. Good times with Dad! Todd and Ryan got the full package. Englund was able to lead the men into an unforgettable riding experience like they had never imagined. Beyond tired, they had to make it to the next town for the night. They rode a section that is typically a two day ride, all in the scope of one day and a little bit of night. "My hand is so tired I can't squeeze the clutch anymore." Ryan said as the cramping in his forearm curled up his hand. When it comes to an exotic dirt bike adventure, MotoMission Peru has the holeshot. With countless untouched routes, an epic landscape, and a personable and capable guide, you owe it to yourself to check out this little gem in the Andes. You can reach Scott at Scott@motomissionperu.com to find out more about tours and riding in the Andes. He is always ready to talk shop! Also, don't forget to "FOLLOW" this blog if you want to have access to MotoMission Peru's new posts and videos.
If you’ve ever experienced a ride or race where your crankcases got damaged in some way, whether from a rock or engine failure you know just how painful dealing with the aftermath of damaged crankcases can be. For those of you who haven’t had to deal with crankcase issues, consider yourselves lucky and know that if you stay in motorsports long enough, your time will come. Late last year I picked up a 2005 Honda CRF250 project bike (click here to read about it) which came with crankcase damage. The crankcases had the following issues: Stripped right main bearing retainer bolt hole Broken off right front shift shaft boss/bore Partially broken off cam chain guide I chose to repair the crankcases because it can be a much more cost-effective solution than buying brand new cases. In this post, I’m going to cover crankcase repair options and tips that may help you save your next set of injured cases when the need arises. While you may or may not be equipped with a welder or feel comfortable carrying out the repairs, the information provided will be equally helpful when discussing repair options with your local welder or fab shop. Strength Considerations First off, since the crankcases house the heart of the engine, consideration should be made as to how structural the repair area is to the functionality of the engine. Secondly, the likelihood of making a repair that results in a joint that is equally strong to the original in critical areas should be considered. If the criticality of the joint is deemed too high or the repair is too difficult, then it is advisable to pursue a new set of cases instead of risking a mediocre repair that could jeopardize future operation. Many people often question whether or not a welded joint or the weld material is as strong as the base material used to manufacture the crankcases? The answer to this is, it depends. The specific casting process used to make the crankcases has a significant effect on how strong the cases are and whether or not the manufacturer chooses to heat treat the cases after casting them. The strength of the welded repair is only as good as the weld itself. Cleanliness, depth of penetration, and skill all play into how strong the repair will be. Most of these variables are relatively controllable; however, skill and experience are primary drivers. Since engineering data that outlines what materials and processes manufacturers’ use to make their crankcases isn’t available, it is impossible to say with any certainty that a weld repair will be as strong as the original material. However, it could also be stronger or weaker. We simply don’t know without testing or analysis. Personally, based on my knowledge of casting processes and how I believe most engine cases are made I don’t believe the alloys used to make weld repairs on crankcases differ significantly in properties from the base material. Repair Methods Outside of welding, there are a couple of other repair methods worth considering depending on the issue at hand. With proper preparation, epoxies (think JB Weld or equivalent) can be used to fix minor issues. For stripped threads, heli-coils or increasing the tapped size can be good options. Welder Types Both MIG and TIG welders can be set up to weld aluminum; however, in my experience, it is preferable to use a TIG welder because they offer significantly more control throughout the welding process. Due to the thick walls found in many crankcases using a welder with enough amperage is imperative. For most dirt bike applications a welder capable of at least 150 amps will be necessary. Welding Best Practices Preparing the Damaged Area - Since untreated aluminum oxidizes when exposed to oxygen, the area being repaired should be prepped by grinding away the surface layer in and around the joint. The material can be removed with a die grinder and an appropriately sized bur. Depending on the area and geometry of the repair it may be necessary to groove out the joint so that additional surface area and weld depth can be achieved. Check Flatness - Before welding, take the opportunity to assess the flatness of all the crankcase mating surfaces. This initial assessment will serve as a benchmark to compare against once all welding is complete. Cleanliness - The cleanliness of the area to be repaired is critical to the success of the job and to keep frustration levels low. Carefully clean the crankcases using isopropyl alcohol, acetone, or other suitable cleaners. Be sure to verify whatever cleaner you use will not emit harmful potentially life-threatening chemicals should you inadvertently expose them to high temperatures and argon gas. Brake cleaners are typically a no-no since they may contain Tetrachloroethylene which can become fumes of phosgene when exposed to high temps. Phosgene, even in small doses, can be lethal. If the crankcases are very porous, an initial cleaning can be performed to remove most of the oil. The cases can then be baked at around 250°F (121°C) for 15 minutes, which will help draw out oil from beneath the surface. The cases can be cleaned again. Filler Rod Choice - 4043 filler rod should work well for most castings and is what I used to carry out the repairs on my CRF250 crankcases. Alternatives to consider include 4047 and 4943. 4047 filler rod offers improved resistance to porosity over 4043 due to its higher silicon content but offers slightly less strength. 4943 filler rod was designed to be an improvement over 4043 and may offer additional strength while retaining similar flow characteristics. Preheat - Heating the crankcase in the oven and raising its temperature before welding will help reduce distortion post welding and make welding the part easier. Oven temps up to 300°F (149°C) and bake times up to 30 minutes can be used to preheat the crankcases. Limit Distortion - Distortion is a risk anytime something is welded and due to the criticality of the location of bearing bores, shafts, and other features found within the cases everything possible should be done to limit distortion throughout the welding process. What can be done will be situation dependent, but the following are recommendations that can be implemented when practical: Preheat the crankcases Make weld repairs with the case halves bolted together Clamp a single case half to a flat surface if the repair permits Leave bearings in their bores Check Flatness - Upon completion of all repairs, check mating surface flatness before returning the case to service. If mating surfaces are not flat corrections can be made on a surface plate or via milling in extreme cases. CRF250 Case Welding and Repair - My CRF250 cases welded well, and I was able to get proper fill with minimal porosity. The weld layers built nicely as I filled in the cam chain guide, shift shaft boss, and bearing retainer hole. Post welding I carefully machined in a new bearing retainer bore, and shift shaft bore. My case did not distort due to welding but had some knicks and dings on their mating surfaces, which I addressed using my surface plate and sandpaper. Upon completion of all the work, I inserted the dowel pins and shift shaft back in the cases and checked fitment of the shift shaft in the new bore. Everything lined up well, and the case halves and shaft mated perfectly. Wrap-up I hope you enjoyed this write-up on welding crankcases and that you consider it as an option the next time your cases incur life-threatening damage. I’m looking forward to moving my CRF250 project forward and taking the next steps to get my engine running. If you want more engine building knowledge at your fingertips, check out my books on two and four-stroke engine building. The dirt bike engine building handbooks are nearly 300 pages apiece and share a wealth of knowledge, such as repairing crankcases, which you won’t find in your service manual when it comes time to rebuild your engine. Check them out on our website or on Amazon. Thanks for reading and have a great week! - Paul
Have you ever ridden a buddy’s bike and walked away wishing that you didn’t have to get off because everything just clicked as you were riding it? On their bike, you could rail every corner, absorb every bump effortlessly, and feel completely stable at high speeds. Once you got back on your bike it feels slow, riding over rough terrain wears you out, and taking corners is best described as unpredictable. To make matters worse, you and your buddy could have the exact same bike! What could possibly account for the huge gaps in handling between the two machines? By design, numerous tweaks can be made to significantly influence how your dirt bike handles. Some of these alterations are as simple as turning a few adjusters, while others require more involved labor such as disassembling forks to swap out springs and dampers. Today’s focus will be on introducing all the different variables that can be adjusted, which ultimately impact how your bike handles. This is the start of an in-depth series on motorcycle handling where I’ll be going into extreme detail on how to make adjustments to individual areas on your dirt bike. For the sake of clarity, I’ve broken out all the things that we can consider adjusting into two categories: geometry variables and suspension variables. What is challenging about tuning the handling of a dirt bike or motorcycle is that all the different options available to adjust are in one way or another interconnected. This means that geometry variables often influence suspension variables and vice versa. If we consider the bike as a whole we have: Center of gravity - The center of gravity is simply a point in space where, if we consider the weight of all the bikes components, the distributed mass sums to zero. For visualization purposes, the center of gravity is a hypothetical point in space where the entire weight of the bike is concentrated. For our purposes, these definitions may not seem particularly tangible, however, what is important to consider is that the center of gravity’s position will have a significant influence on the bike’s stability and handling. Wheelbase - The wheelbase defines the distance between the front and rear tires’ contact patch. Wheelbase adjustments will affect how stable the bike feels. Weight Bias - The weight bias defines the distribution of the bike’s weight between the front and rear wheels. Seat Heat - Seat height can influence handling by altering the combined center of gravity of bike and rider as well as be an ergonomic consideration. Ergonomics - Ergonomics refers to all the small adjustments that can be made to make the rider feel comfortable on the machine. Examples include shift and brake lever position, seat height, handlebar position, and foot peg location. Front geometry variables include: Ground Trail - Ground trail is a measured or calculated distance used to compare the distance of the steering stem axis (extended to the ground) to the center of the contact patch. Rake Angle - Rake angle defines the angle between the steering stem axis and vertical plane. Contact Patch - The contact patch is the portion of the tire that is in contact with the ground. Triple Clamp Offset - Triple clamp offset defines the center point distance between the fork tube axis and steering stem axis. Axle Offset - Axle offset defines the center point distance between the axle and fork tube axis. Total Offset - Total offset accounts for both the axle and triple clamp offset. Front Wheel Diameter - The measured diameter of the wheel. Most of the parameters discussed here all influence ground trail, which is a key variable used to assess the bike’s stability. Rear geometry variables: Swingarm Angle - The swingarms angle relative to the horizontal or ground plane. Contact Patch - The contact patch is the portion of the tire that is in contact with the ground. Front and Rear Sprocket Diameter - The sprocket’s pitch diameter. Rear Wheel Diameter - The measured diameter of the wheel. The rear end variables outlined here are not particularly important when considered on their own but have a significant influence on a critical handling concept called “Anti-Squat.” Anti-squat is used to characterize the effects the swingarm angle, and chain force has on the rear suspension. Anti-squat will be explored in further detail in a future post. When it comes to suspension, numerous adjustments can be made to influence the bike’s response. These include: Fork and Shock Preload - Fork and shock preload quantifies how much the fork or shock springs have been compressed upon installation. Preload adjustments predominantly affect the ride height of the bike. Fork and Shock Compression Damping Adjustments - Compression damping adjustments alter the suspension system’s response to events that compress the suspension. Fork and Shock Rebound Damping Adjustments - Rebound damping adjustments alter the suspension system’s response to events that extend the suspension. Fork and Shock Compression Damping Selection - Significant alterations to the way the forks and shock respond to compression events can be made by swapping out dampers or modifying existing dampers. Fork and Shock Rebound Damping Selection - Significant alterations to the way the forks and shock respond to extension events can be made by swapping out dampers or modifying existing dampers. Fork and Shock Spring Selection - Fork and shock springs are selected based on their spring rate. Different applications and riders require different spring rates to optimize the suspension system. Fork Oil Level - The volume of air found within a fork acts as an air fork. The air volume can be increased or decreased by adjusting the amount of fork oil used. Fork and Shock Oil Viscosity - Viscosity is a measure of an oil’s resistance to flow. Changes to oil viscosity in the suspension system will affect how the damping system responds. Front and Rear Tire Pressure - Tire pressure settings influence traction and also the overall response of the suspension system since tires also act as air springs. Shock Linkage Ratio - If the bike is equipped with a linkage that connects the shock and swingarm the geometry of the linkage can be manipulated to alter the shock's response. I hope this overview of all the different variables that can be manipulated to improve the handling of your machine has you excited for what’s to come! Making a dirt bike or motorcycle handle well can mean the difference between a podium finish and a mid-pack finish when racing. It can also make or break the riding experience when out on the track and trail. The number of variables that can be altered can seem overwhelming, but in future posts, I’ll walk you through a systematic approach to make the job less daunting. If you want to stay up to date on the latest tips and info I have available regarding dirt bike handling and suspension I want to invite you to sign up for my email newsletter on the subject. Click here to sign up and I’ll keep you in the loop! - Paul DIY Moto Fix