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. |
 Use your thumbnails to pry apart the first bushing. It is usually pretty easy, and when spread just a bit, it will easily slip off the end of the fork tube. The cleaned bushing should be uniformly gray on the outside. If the underlying brass is showing through at any point, look for damage inside the outer fork tube. Your quick and dirty fork seal change is over, and you'll need additional special tools. |  The rest of the parts slide right off. Lay them out in the order they come off. The washer that goes between the seal and the bushing isn't too critical for this Showa, but a Kayaba has a machined part that must go in the way it comes out. The second bushing should have the uniformly gray color inside. If the brass shows through in streaks, look for significant damage in the steel inner tube's surface. |  Clean the tube extremely well, then under good light, inspect it for nicks that may have cut the seal. Use a razor blade to judge any imperfections you see. If the razor catches on any small pits, they will need to be dressed and have the edges removed before the new seal is put in. Nicks will almost always be at the back of the fork tube. Deep or large scrapes or gouges may not be repaired successfully. To keep the fork light, the outer tubes are very thin, and they can be dented right through fork guards in a crash involving another machine. The inner tube must be replaced if the damage is major. |
 Small nicks from the front tire hucking rocks at the rear of the tube can be dressed. I use a fine-grit, tapered sanding tip like this one in a Dremel tool. A Scotch-Brite tip or a Cratex tip (grit in a rubber compound) work well, too. Don't get carried away. You just want to knock down the edges. As soon as the razor blade will slide across the nicks without catching, the nicks won't bother the seal. |  Dump the oil from the outer fork leg into a drain pan. Make sure the oil drains completely. Once the outer tube has emptied, push in the cartridge rod and release it. It should spring back to full extension if the cartridge is still pressurized fully. If the cartridge rod doesn't return, the inner cartridge must be serviced, and it will require more special tools. |  Since we are only dealing with the outer chamber oil, we can fill it from this end and not bother with removing the top fork cap or the cartridge. The manual will tell you the correct volume. We put in 10cc less than the specified amount since we couldn't be sure that the outer tube was completely drained. |
 To complete the reassembly you will need another special tool, but you can make this one out of a plastic sandwich bag. Cut off the corner of a quart-size bag. |  Set the bag corner aside and use some light grease on the seal and the wiper. |  Put the cut bag over the end of the steel fork tube. Without the bag, the machined edges where the fork bushing sits are very sharp, and they will cut the seal while it goes on. |
 Slipping the greased seal over the bag keeps the seal safe. Slide the wiper on first, drop on the snap ring, then carefully work the seal over the bag and the sharp edges. After the seal is on, remove the bag corner and slip on the spacer and bushings. |  The assembled inner leg should look like this. Set it aside while you prep the outer tube. |  With the fork in an appropriate vise or held upright by your helper, ease the fork spring over the cartridge rod. Slide in the damping adjuster tube. The bottom end is indexed in a Showa, but not a Kayaba. The rod will only drop in fully when it is rotated correctly. On the Showa the rod is below the top of the cartridge rod, but on a Kayaba it extends a bit above the top of the rod. |
 Slide the inner fork tube over the fork spring and damping rod. |  Slip the seal and wiper up near the axle clamp. The bushing on the end of the steel tube will slide right in. The other bushing will need to be forced in. Let the spacer sit on top of it as shown. |  Use a seal driver like this one from ESP (818/249-6744) to drive in the bushing. Seal drivers are available from Race Tech, Motion Pro and the bike manufacturer. It makes this job easy. |
 When it fully seats, the seal driver will generate a solid clack. You will hear the difference in the sound when it is in right. |  After the bushing is seated, slide down the seal and start it in with your fingers. Use the seal driver to knock it all the way in. As with the bushing, when the seal seats it will produce a solid, sharp sound. Plus, when you look in the seal bore, you will see that the snap ring groove is fully exposed, so the snap ring will seat easily. Push in the snap ring with your fingers, then use light pressure from the seal driver to lightly seat the snap ring all the way around. Inspect it visually to make sure it is seated. |  Use your fingers to push in the wiper. The seal driver is not shaped to drive the wiper in without damaging it. It takes a good push but will go in with just finger pressure. |
 Push down the fork tube and slide the special tool or a 12mm wrench under the lock nut. Thread on the base bolt. There is a rod that extends from the base of the Showa bolt, and it has one flat side. The small rod inside the cartridge rod also has one flat side. Make sure the rod is inserted into the tube correctly before you thread on the base bolt. Use a torque wrench to tighten the base bolt against the lock nut. The manual has the torque specification. |  The base bolt is then torqued into the axle clamp casting. This torque figure is much greater than the torque against the lock nut. Use the axle to hold the fork while you tighten the bolt. All that is left is to put the fork legs back on the bike. Remember how you counted the rebound clicks? Set the rebound back to the number you counted before you ride. Once you do this a couple of times, a fork seal will be a 30-minute job. |