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.