Fork Rebuild Secrets With Race Tech - Dr. Dirt

13 The damping pistons and valve shims are held on with a nut that's locked on by mushrooming the end of the shaft. To remove the nuts it's necessary to file or grind the spread or mushroomed part of the cartridge rod and the compression base valve. Williams has the control to grind it. We'd recommend a file.

14 Once the staked end is ground smooth, the nut holding the valve stack on should come off easily. Race Tech uses a wire bent into a "J" shape to remove the parts. The wire is held against the threaded end, and the parts slide up onto the wire. The wire is flipped over, and the parts are held in the crook of the "J" for cleaning.

15 The valving shims must flex to control the flow of oil through the damping pistons. Eventually that flex will fatigue and wear out the shims. If the shims have wear marks, then they should be replaced. These aftermarket blue shims are easier to see wear on than silver ones, but the wear still shows on the silver ones.

16 The wear patterns on this damping piston illustrate the surface is no longer perfectly flat, so sealing is compromised. Race Tech surfaces the pistons on a 120-grit adhesive sanding disc stuck onto a square of plate glass. This returns all of the sealing surfaces to true flat for correct sealing.

17 Both sides of the piston (new, used, stock or Gold Valve) are surfaced until the sealing faces are uniformly shiny. This fork was already modified, but if you're going through the trouble of replacing the shims, the jump to a Gold Valve kit to get new parts and updated valving is a good idea.

18 Polish the cartridge rod by hand with 000 steel wool. You only need to worry about the portion of the rod that the seal touches during full travel. You don't need to buff it like chrome, but clean it up. Steel wool leaves micro-slivers of steel wool around, so clean the parts well with contact cleaner before using the cartridge rod.

19 Clean the parts of the damping pistons with a cleaner that doesn't leave an oily residue. Williams built a new shim stack with new shims, then assembled the base valve and cartridge rod. Instead of staking the nuts, Race Tech uses red Loc-tite and torques the nuts to 45 inch-pounds.

20 If you find deep scratches like this, Race Tech suggests replacing the legs ($230-plus each for this fork, but cheaper than quality replating). The company won't warranty the seals if there are deep scratches present. Race Tech mounts fork legs on a specially modified drill press and buffs the surface with 500-grit emery cloth. Deeper scratches must be dressed with a super-fine dressing stone.

21 Like the inner chrome tube, the outer aluminum tube should be inspected for damage. Hold up the cleaned tube to the light and look through it. The shiny oval you see is a hole worn through the hard anodizing. New tubes for this fork are almost $500 each. Race Tech can hard-anodize the tubes (clear or black) for $100 each.

22 With all the parts cleaned up and repaired where necessary, it's time to start reassembly. These are the new parts that are going in this fork. Race Tech offers them, but everything except the blue cartridge seal can be obtained from your dealer. We also installed new shims, though they aren't shown here.

23 Each seal and bushing is installed with Race Tech seal grease. The bushings are greased on both sides, and the seals get enough grease to make them slide easily for assembly and when the fork is first used. That is a light coat. You don't want any gobs of grease in the system.

24 Before installing the bushing holder back on the cartridge rod, it needs to have both surfaces clean and free from grease and oil. Then apply red Loc-tite to make sure it won't come loose. Many of these parts are made with extremely fine threads in aluminum, so they can't stand a lot of torque.

25 Once the bushing holder is torqued, you can grease the piston band on the cartridge rod before sliding it up into the cartridge body. The bottom of the cartridge is open until the base valve is installed.

26 With the cartridge rod in the cartridge body and the rod extending up through the bushing, the hydraulic bottoming stop piston can go back on. Be careful not to lose the small clips. Thread the two halves together and tighten them. Don't go crazy leaning on the wrenches.

27 You can cut the corner off of a sandwich bag to cover the sharp edges on the fork tube, but Race Tech sells these cool narrow bags for the purpose. The plastic bag keeps the machined edges from cutting the delicate seal lips. With the grease on the inside of the seal it will slide right over the bag.

28 The fork cap is locked to the cartridge rod with a lock nut. Kayaba forks on bikes made from 1989-'95 can have the rod break right at the threads. The problem has been traced to vibration, and it's worse on 500s than other models. Race Tech has made a longer brass nut, and it solved the problem.

29 Our fork had a stack of preload spacers in each fork leg. Williams decided to check the preload. With the cartridge fully assembled (but outside the fork) and the cap on, set the spring against the spring seat and then measured to the top of the spring and to the bottom edge of the fork cap. We had 490mm to the top of the spring and 500mm to the cap.

30 Williams measured the stack of preload washers with a digital caliper, and the measurement was close enough to 15mm. Since the accepted norm for fork spring preload is 10mm, the fork needed the spacers it had been using.