Front forks of a motorcycle not only hold the front wheel in place but serve as impact absorbers (springs) and bounce dampeners (shocks). The following diagram shows a cross section of a typical assembly. It is actually a tube within a tube. The fork tube is attached to the frame while the slider(tube) is attached to the wheel. As the wheel hits a bump the slider is forced upward compressing the spring and absorbing the force. The spring recovers and the slider returns to its normal position. To stop the wheel from compressing too far and to prevent any bouncing as the slider recovers, a hydraulic system kicks in. As the slider pushes upward, oil is forced through small holes in the damper valve and enters the fork tube. As pressure is released on the slider, the spring forces the slider down and oil is drawn back into the lower slider chamber. The fork seal scrapes oil from the fork tube, much like a piston ring, and also prevents oil from leaking out between the slider and fork tube.

Fork Diagram

Normally, maintanance involves changing the fork oil every year or so and replacing the fork seals when leaking is noted. The following is a generic step by step procedure to follow when changing your fork seals.

1) Open the drain valve from one of the forks, place a catch pan under it and pump the forks to remove the old oil. Close the drain and clean out the other fork.

2) With the center stand down, place a jack or other support under the engine or front portion of the frame and lift the front wheel from the ground.

3) Remove the wheel, fender, disk brake or drum brake cable and speedometer cable. Some bikes may have part of their headlight assembly attached to the forks also so their removal is required.
CAUTION: support the hydraulic brake caliper so its weight isnt on the fluid line, old ones may crack.

4) Loosen the triple clamp bolts that hold one of the forks and slide out the fork.

5) Carefully remove the top tube cap.
CAUTION: there may be some pressure due to the internal spring! Remove the spring. Some models have a top bolt holding the spring, if so remove it also, carefully.

Ring Clip6) There should be some kind of circlip found where the fork tube and slider meet, just atop the fork seal. Remove the circlip using a pair of circlip pliers.

7) On the very bottom of the fork you will find a bolt that holds in the damper rod. Remove the damper rod securing bolt and slide out the fork tube. This may also pull out the old fork seal.

HINT: Honda made so many different versions of front forks I cant go through all of the variations on this theme, but this is a general model!

8) If the fork seal is still in place, work it out with a pair of needlenose pliers.

9) Inspect the fork tube for pit marks. If you see many, the fork may still leak even with a new seal or it may wear out the seal at an accelerated rate.

10) Apply fork oil to the inside of the fork seal and slide the new seal over the fork tube. Replace the fork tube, and other goodies(washers etc.), in the slider. Reattach the damper rod with its bolt.

11) The truely hard part is now at hand! The seal must be pushed back into place with an even pressure all around the fork tube. The only way to accomplish this to to slide a pipe or other tube over the fork tube that is about the same size as the new seal. With an even push, press down on the pipe and seat the fork seal.
CAUTION: if you are not careful, you can damage the seal! Most seals have a small spring that holds the internal rubber lip against the fork tube, make sure it is unharmed! HINT: Honda sells a tool that can be used to seat the fork seal if this procedure just doesnt work.

12) Reassemble the one fork (dont forget the circlip) and before placing on the top cap, refill with oil as per the manual.

HINT: Automobile transmission fluid should be used as front fork oil.

13) Repeat with the second fork, replace and refill.

14) Reassemble the front end of your bike.

Hopefully the forks will no longer leak.

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