Fix Your Fork Seals with Seal Mate! http://www.sealmate.net Sealmate is the one and only tool that will instantly repair leaking fork seals! R&J Engineering has invented this tool that will fix the leaky fork seals without the cost of removing and replacing them.
Leaky fork seals are, for lack of a better description, a royal pain in the neck. The most common ailment to plague front suspension, a leaky fork seal can ruin your day by affecting your bike’s handling, covering your front brake pads in oil and generally just making a total mess of things. Most of the time a leaky fork seal is the result of dirt inside of the seal, but it can also be caused by a nick or ding in the fork tube from an impact with a rock or stick. But no matter what the cause, a weeping fork seal needs to be fixed, and oftentimes that means tearing into the suspension and changing the seal out. Fortunately, this isn’t as difficult as you may think.
Dirt Rider tech guru Scot Gustafson (the man behind the Dr. Dirt tech stories here on www.dirtrider.com) insists that changing afork seal is easy enough for most riders to do in their own garage. To help prove his point, we filmed Scot changing a fork seal in the Dirt Rider tech center and explaining step-by-step how he completes this job. You might want to bookmark this video for reference because someday, no matter if you ride motocross or off-road, you’re going to need to address this issue!
If you have any additional questions, please feel free to email Dr. Dirt at drmail@sorc.com, subject: Dr. Dirt. Enjoy!
Yesterday at the race track we had a discussion about what is the right size tire for a 250f diretbike and the local guy selling tires at the track not a tire distributor, was saying it was a 100/90-18 and that is the best tire for the bike. I totally disagree I recommended a 110/90-18 on a 250F. He was arguing with me about it but I have been around a lot of the top racers not just a local track guy in New York and I again will disagree. I know a lot of good riders using a 120/90-18 on a 250F and there are a lot of variables for tire size with weight, power etc you get the point. But I need to know all you riders out there please tell me what size tire you are running on your 250F four stroke. I was also told that we are the only ones running a 120/90-18 on our 450F because no one else would run that tire. Please no matter what motocross or supercross bike you have let me know what size tire you are running.
You replace your rear tire because you can see the signs of wear, but the signs of clutch wear are trickier to spot. You can lay your bike over and pop off the clutch cover easily enough, but what do you look for then? Ron Hinson of Hinson Racing demystifies basic clutch inspection.
01. You should have 1/8 to 1/4 inch of freeplay at the lever. To check, pull the cable assembly away from the perch, then pull in the lever and watch the gap between the lever and perch before the cable engages the clutch. (If you use the quick-adjust when riding, reset the freeplay after the bike cools.)
02. Stock steel clutch plates are an unfinished aluminum/silver color. If your plates are blued, then these plates, the fiber plates and the springs have all been heat damaged and should all be replaced. If there’s no heat damage, check the steel plates for flatness and measure the thickness of the friction plates (check your owner’s manual for specs). Springs cannot be tested by length. Stock springs are stiff enough when new, but their rates go away easily when exposed to heat. Replace them often-every 10 hours for clutch abusers.
03. Check the clutch basket ears for notches. These will cause the clutch to drag and make engagement/disengagement sticky. Filing these smooth is a bad idea-you can create an edge that could break plates or uneven contact points between the different tangs, and you will be taking off any hard coating. (A telltale sign of a notched basket is if the bike won’t shift into neutral easily.)
04. Check the inner hub splines for grooving. Same rules apply here as to notching/grooving on the clutch basket ears.
05. Reassembly: Petroleum oil is better than synthetic oil for the clutch. In a motor that shares trans oil, the oil will become contaminated from the clutch long before it degenerates, so the long-lasting benefits of synthetics are wasted. Use high-quality pure petroleum and change it frequently. (Do not use any oil with moly.) Install the steel plates with the rounded edges toward the inside of the motor. Soak new fiber plates, ideally overnight, in the same type of oil you will use in the transmission.
We’ve all heard the argument, “I can’t justify buying a new $9000 bike because I’ll also have to buy a pipe, get my suspension revalved, get my engine done, etc”. A stock bike can be tuned to perform like a highly modified machine if you know where to start. These tuning tips will help make your bike work better and they are mostly free.
DLC coated fork legs – One of the benefits of DLC and other fork leg treatments is less friction than a standard chrome tube. A major source of friction are dry fork seals. Before you ride insert a thin feeler gauge under your oil seal and turn it a little so fork oil can lubricate the seal. Your forks will act and feel like more expensive units.
Oversized Brake Rotors – Almost all factory bikes have oversized rotors that produce incredible stopping power. The thing you don’t see is that the rotors are free of oil, grease and cleaning chemicals that hurt braking performance. Clean your rotors with brake contact cleaner before every ride to increase stopping power. Factory bikes also get their brakes bled before every race. Fresh brake fluid and a system free of air and moisture make for strong brakes.
Offset Triple Clamps – The main reason to change your clamps offset is to give a better steering feel. Some bikes have too little front end traction while others have too much. By changing the position of your rear axle you can increase the steering feel of your bike. Simply sliding the rear axle back puts more weight on the front end of the bike. Sliding it forward takes weight off the front and puts more weight bias toward the rear. To do this you will have to add or remove a chain link, or change your gearing. Adding or removing a chain link moves the axle about 14mm in the swingarm. You will need to reset your sag when you change your wheelbase.
Exhaust pipe – An aftermarket exhaust pipe is an easy way to make horsepower. If you have a fuel injected bike try changing the ignition clips or remap your ECU. By altering your fuel mixture and ignition timing you can give your bike more power. You can also make your bike more rideable when track conditions or rider ability dictate a need for less power.
Fuel Injection – A properly tuned Keihin FCR carburetor can be as responsive as a fuel injected bike. Try tuning the low speed and accelerator pump circuit in your carb. The fuel screw controls your air/fuel mixture at idle. Your leak jet controls the volume of fuel in your accelerator pump. The pump timing screw controls when your carb squirts fuel and allows the accelerator pump to refill. Keeping the accelerator pump nozzle clean will insure your carb sprays instantly.
Revalved Suspension – Nowadays, stock suspension is excellent, especially if you know how to tune it. Simply setting the sag will make a bike perform better. Increasing your fork oil height or volume will increase your forks bottoming resistance. Decreasing the oil will give the fork more linear damping for a plusher ride in the middle part of the stroke. When done properly, your compression and rebound clickers allow for endless tuning possibilities. A major component in suspension tuning is your chassis. Try re-torquing all your motor and frame bolts to the manufacturers spec. This will give your frame the optimum amount of flex for comfort and control.
Handlebars – Many bikes today have offset handlebar mounts and multi-position triple camps for better rider ergonomics. If you need a taller handlebar try installing a flat washer under the bar mount to increase the handlebar height 2mm to 5mm when you can.
Throttle Tubes and Clutch Levers – Aluminum throttle tubes and billet clutch perches have very little friction, close tolerances and work effortlessly. Lubricating and cleaning your stock controls will go a long way to bridge the performance gap between the two. Use a lubricant that doesn’t accumulate or attract dust and dirt. Most stock controls offer easy height and reach adjustments for better fit. A strip of Teflon tape under the brake and clutch clamp will help the controls move in the event of a crash.
Factory Bike Power – Adjusting the position of your fuel injector or accelerator pump nozzle to optimize where it sprays is a factory race trick that can gain a horsepower. OEM bikes come with air filter backfire screens but they aren’t on factory race bikes. And finally, Pro riders hold the throttle open longer and brake later…and that doesn’t cost anything!
How often do you think the brake fluid on a professional race bike gets changed and bled? If you answered every race, you would be correct. How often do you change and bleed the brake fluid on your bike? If you haven’t serviced your brakes in the last year, you are overdue. Brake fluid goes bad because it attracts water, gets contaminated or overheats. Fresh brake fluid is light in color and, like gasoline, it becomes darker when it begins to go bad. Off-road bikes usually use DOT 3, 4, or 5.1 grade brake fluid. In general the higher the number the better the quality and the higher the boiling point. Brake fluid will attract water after a bottle has been opened so it is best to use a new sealed bottle whenever you replace your brake fluid.
Start by looking over the general condition of your entire brake system. Replace worn brake pads before you bleed your brakes. If you bleed your brakes with worn out pads you will add more oil to your system than normal and can cause your brakes to lock if you install new pads later. Replace your brake pad springs and retainers if they are worn or damaged. If your brake pin is worn replace it or sand off the corrosion to restore the polished finish. Rotors need to be straight and checked for uniform thickness. If your brake levers are bent or pivot bushings are worn replace them to restore the feel and action.
The easiest and most effective way to bleed your brakes is to reverse bleed your system. Since air always rises, it is more effective to push the old fluid and trapped air from your calipers at the bottom to your master cylinder at the top. Fasten a short length of hose to a syringe and fill it with fresh brake fluid. Brake fluid can damage plastic and paint so wrap the brake reservoir and bleeder with a towel. Brake fluid is also toxic so wear gloves when you work with it. Hold the syringe upside down so any trapped air will flow upwards toward the plunger and away from the hose. Open the brake bleeder and push the fresh fluid into your caliper until you see it come out in the master cylinder.
Drain off the excess fluid in the master cylinder by siphoning it out with a second syringe. Continue pushing fresh fluid into the cylinder until it displaces all the old fluid. Close the bleeder and set the fluid height in the reservoir about 3/4 full or to the top of the sight glass window. Pump the brake lever until it has it has a firm, solid feel.
If your brakes still feel spongy after bleeding you should check the key areas for problems. Air frequently gets trapped in and around the banjo bolts, so simply loosen the bolts to release air pockets and re-bleed as necessary. Make sure the banjo bolt washers are not leaking. Check for any leaks along your brake lines. Often the seals on your master cylinder piston will get worn out or damaged and need to be replaced. The same is true for the seals around the pistons in your caliper. Sometimes, simply pumping the lever a good number of times will restore the positive feel.
If you want your lever to have a really tight feel you can bleed off any remaining microscopic air molecules in the system by securing the brake lever to the handlebar with a zip tie overnight. Clean off any excess fluid you may have gotten on the caliper and master cylinder with contact cleaner.
Finally, clean your rotors with contact cleaner and a lint free cloth to complete the job.
Want more Dr. Dirt Wrenching Tips? Check out the Dr. Dirt section of Dirt Rider magazine, or stay tuned to the website for future stories and info. To suggest a topic for an upcoming installment or to ask Dr. Dirt a tech question directly, send an email to drmail@sorc.com, subject line: Dr. Dirt.
You can have the best suspension in the world but if you don’t maintain it or understand how it works it’s not worth much. Before your next ride follow these few simple tips to improve your suspension and get the most out of your bike.
- Tire Pressure – Begin by making sure your bike has the proper tire pressure so it will handle it’s best. A bike with too much air in the tires will be harsh and deflect off obstacles while an under inflated tire will distort under load and not give good rider feedback. Use 11-13 psi for motocross and 13-14 psi or more for off road to prevent flats. Heavy tubes and mousses will greatly affect your bikes suspension so aim for the lightest possible set up you can without risking punctures. An 18″ rear wheel also has more rider comfort than a 19″.
- Proper Spring Rate and Sag – Your springs hold up the rider and bike so make sure you have the proper rate spring in your bike. Most bikes work best with 95-115mm of sag when the rider is on the bike. Once you have the rider sag, check the static sag of the bike without the rider. Static Sag should range between 25-45mm. If the static sag is less than 25mm you need a stiffer spring and if it is greater than 45mm you need a softer spring.
- Install your front wheel correctly – Install your front wheel squarely with the forks before tightening the axle pinch bolts and axle nut. Improper installation will cause the forks to bind and wear quickly. Begin by tightening your axle nut first then torque the left side axle pinch bolts to spec. Make sure your right fork leg will slide easily along the axle before tightening. Compress the fork to set the leg and tighten the right pinch bolts when you are sure the fork leg is not binding and in it’s natural position.
- Use a torque wrench – Never over-tighten the triple clamp bolts because the fork tubes are very thin and will distort easily. Check your owners manual for the proper torque spec. Your fork bushings travel past the lower triple clamp mount and can bind if the clamp is over-tightened and cause the fork to be harsh. Be sure both fork tubes are mounted at the same height. You can also vary your bikes turning and stability by raising and lowering the forks in the triple clamps.
- Bleed the air out of the forks every time you ride – Bleed the air out of your forks at the beginning of the day before you ride. Always bleed the forks with your bike on a stand and your front wheel off the ground. Air expands with heat and altitude so it is important to start your ride with no excess pressure.
- Maintain your suspension – Change your fork and shock oil every 20 hours and replace wear parts like bushings and seals every 40 hours. Oil breaks down and gets contaminated over time causing your suspension to fade when it heats up. Worn bushing are also a cause of leaky seals and friction because of excess play. Most modern dirt bikes specify the use of 5wt fork oil. Shocks run at higher temperatures and use lighter 2.5wt oil so they don’t fade and breakdown as quickly.
- Fork Oil Height – Adjusting the fork oil height alters the amount of air space in the fork and changes the damping characteristic in the 2nd half of the suspension travel. Adding oil stiffens the fork and increases bottoming resistance while removing oil softens the fork. Add or subtract oil in small 10cc gradients until you get your desired effect . You can add fork oil through the air bleeder with a small syringe. To remove oil, you will need to remove the fork legs from the bike and turn them upside down to drain oil out of the air bleed holes.
- Grease your linkage and headset – Clean and grease your pivot bearings to maintain performance and minimize wear. A properly maintained linkage will move more freely and have less friction so your suspension will work better. A headset that is properly adjusted and greased will give accurate rider feedback.
- Chain tension and length – Adjust your drive chain on a stand with 30-40mm of play so it will not bind when the rear suspension is fully compressed. Running a longer wheel base will offer more straight line stability while a shorter wheelbase offers improved turning. Running the axle forward lessens the leverage on the shock and stiffens the initial suspension movement. If you want softer suspension in the beginning of the travel, you can move the rear axle rearward to increase leverage on the shock. Gearing you bike higher with less teeth on the back sprocket will give for better traction because of lower engine speed.
- Troubleshoot your suspension -Learn to troubleshoot your suspension for better performance. Suspension that bottoms out too easily might need more compression from your clickers, more compression valving, a higher oil level, stiffer spring rate, or just need to be serviced. A rear shock that kicks up over bumps has a different set of problems than one that kicks to the side. When you are testing suspension ride the same lines around the track in order to determine if your changes are working. A good rider can avoid all the bumps on the track and make any suspension feel good.
- Bonus – Pneumatic spring fork tips – Adjust the air pressure every day before you ride with the wheel off the ground. Use a small dial pump with a good no loss air valve. 2 psi is the equivalent of 1 spring rate. The air in the fork will heat up and expand as you ride causing an increase in pressure. Nitrogen does not offer a significant advantage over air.
