Modern dirt bikes have big, beefy forks with comparatively massive inner steel tubes to handle the rigors of current track and trail obstacles. The combination of inverted design and 47-50mm inner tubes solve any flex problems, but they bring their own headaches. For one, when you get big tubes, there is the problem of seal drag, so manufacturers are always treading a fine line between seal life and seal drag. For another, with the inverted design, the seal is trying to hold in oil sitting above it, rather than under it. Making this more difficult, the backs of the steel inner tubes are exposed to debris thrown by the front tire and the lips inside the seal that actually hold back the oil are delicate and easily cut by nicks in the tubes.
A full rebuild of late-model KYB and Showa sealed-cartridge forks requires a variety of special tools, but all the seal does is keep the oil in the outer chamber. If you need just a seal change and not a full servicing, the job can be a lot easier. We looked at ways to do the seal swap with a minimum of special tools, time and mess and found you can accomplish the job with normal hand tools, a vise with soft jaws, a Ratio Rite and a seal slammer. If you have a helper to hold the fork upright, you won't need a vise. We managed the replacement without even taking off the top of the fork. We did the job in an ordinary garage, with moto-kid Chris Dvoracek doing his first-ever fork seal change.
Before you start, clean up the bench and organize your tools. If you plan on doing your own suspension regularly, a suspension vise like this one from Park Tool (www.parktool.com; 651/777-6868) is an awesome addition to a garage. If you mount it so it extends over the edge of the bench, you can also use it to work on bicycles. For a racer like Dvoracek, that is a bonus. You'll need some contact cleaner, fork oil (of the correct weight for your brand of fork) and shop-type paper towels. | 
One of the main reasons you need a special suspension vise or a normal bench vise with soft jaws is to hold the leg while you release the cartridge rod nut in the bottom of the fork leg. The solution is to crack the nut loose while the fork is still on the bike. If you just unfasten it, no oil will come out. Just make sure the ratchet is set to loosen. It is easy to get confused when working upside down. | 
You will need a vise with soft jaws made from copper, aluminum or plastic. We found these magnetic plastic units at a Lowe's for less than eight bucks. Or get a helper to hold the fork upright and forget the vise. Simply put a wood, cardboard or rubber mat under the cap so it doesn't get damaged. |
Since the seal was leaking, the areas near the wiper and the axle holder were covered in oil and dirt. Wipe off the fork before proceeding. Clean the area around the bolt head well. You will be working with the fork upright, and any stray dirt will end up inside the fork. Before you proceed, turn the adjuster all the way in while counting the clicks. Record the setting and then turn the adjuster all the way out. | 
With the fork secured, loosen the base bolt. If you didn't slacken the base bolt while the fork was on the bike, use the front axle to hold the fork while you free it up. Unthread the bolt until it is out of the axle holder. | 
This step is easier with a special tool from Race Tools (www.racetools.com; 585/328-9160), Motion Pro (www.motionpro.com; 650/594-9600) or Race Tech (www.race-tech.com; 951/279-6655). The manual that comes with the bike provides the dimensions to make a tool as well. It is possible to use a 12mm wrench. With one hand, pull down firmly on the inner (steel) fork tube. You need to pull it down far enough to get a tool or a wrench jammed under the lock nut, as shown here. |
Use a wrench to hold the lock nut and a wrench or a socket to break loose the base nut from the lock nut. Then fully unthread the base bolt from the cartridge rod. Clean the base bolt and set it aside. | 
The rebound adjuster in the base bolt compresses this rod. It is easiest to remove it now, so it doesn't drop out when you dump the oil. Set it aside as well. The work bench we were on is well used, so we laid out paper towels to keep the parts clean. Finally, pull down the fork tube and release the holding tool. | 
Use a blade screwdriver to pry up the fork wiper. It should come up easily after you work the tip in between the wiper and the outer tube. |
A wavy snap ring keeps the seal and Teflon-impregnated bushings in place. It is simple to reach in with a small screwdriver and pop out the snap ring. Be careful so you don't mark the tube with the screwdriver tip. | 
Grab the inner and outer tubes firmly, one in each hand. With the fork upright (to keep the mess to a minimum), compress, then rapidly extend the inner fork tube. You use the inner tube like a slide-hammer to pop out the bushings and seal. The seal and bushing will usually pop loose rather suddenly, so be careful. | 
Lay out the parts on your paper towels until you are ready for them. Slide out the spring and lay it down. Some forks have springs that need to go in a specific direction. Check the ends of the springs. Most have lines ground in to one end to identify them. This fork has the springs in with the ground marks down. Prop up the outer fork tube so the oil doesn't dump out yet. |