Replacing your Motorcycle's Fork Seals


Doing basic maintenance and repair on you own motorcycle can be fun and enjoyable, and it can also save you a bit of money. Replacing fork seals yourself, a common task for motorcycle available on the Thai secondhand market, can save you in some cases around 1,500 to 4,000 THB, and with a good service manual and a little patience, it's easy to do.

On a clients older Yamaha 650cc motorcycle, the fork seals were something that had been nagging for a long time. The motorcycle was still ridable, as the forks weren't shooting oil out – yet – but it was obvious that they were seeping oil, and it wasn't a condition that was going to get any better on its own.

As we always like to remind you, before you start any project, make sure you have a good manual specific to your motorcycle. For many motorcycle models you can easily get a service manual online. For our job, our service manual included a few key bits of knowledge that came in very handy, including the amount of oil the forks require, we also found some information on the Internet on how to make a tool to aid in the removal of the damper rod in each fork.

Our new fork seals, we ordered from BikeBandit. The fork oil we bought locally Although Yamaha originally specified single-weight engine oil for our motorcycle's forks, we recommend using an oil specifically designed for use as a fork oil as it will contain desirable anti-foaming and anti-friction additives. Thicker oil can be used to increase the damping of the forks, or thinner oil can be used to soften the damping if it is too strong.
You'll need a jack stand, or some sort of jack or lift to keep the front of the motor in the air once you remove the front wheel. If you don't have a jack stand, a floor jack and some stacked scrap lumber can also be used. Just make sure your motorcycle's secure and won't fall off.

How we start, put the motorcycle up on the center stand. Have a helper sit on the back of the seat of the motorcycle to raise the front wheel off the ground. The average Thai female is the perfect person. Put a jack stand under the motorcycle. We managed to wedge one between the front engine mounts.

After that use a set of pliers to remove the speedometer cable from the speedometer drive. Remove the axle nut on the right hand side of the motorcycle with the right wrench.

Loosen the two nuts on the bottom of the fork leg on the left hand side of the motorcycle. The axle should now be free. Use a rubber mallet or hammer to lightly tap the axle out. Do not damage it... Be prepared for the speedometer drive and wheel to drop out as you remove the axle.

When the speedometer drive drop out. It has a key that sits proud that must be lined up when it is reinstalled. Also, at this time, remove the bolts on each fork that hold the fender and/or fender stays. Remove the bolts on the inside of each fork leg with care, they often touched by corrosion and lot let go easily.

Remove the nut and the nut-headed stud that hold the brake caliper on the fork(s). Remove the caliper and carefully set it aside, still attached to its hose.

Loosen the fork cap using the correct wrench. You just want to break the tension on the fork cap, not remove it. It's easier to do this when it's still on the motorcycle. Loosen the pinch bolts at the top of the forks that hold the forks in the top triple tree, and loosen the pinch bolts on the lower triple tree.

Grab the top half of the fork leg and twist and pull down to work the leg out of the triple tree.

After preparing a drain pan carefully remove the small Phillips head screw at the bottom of the fork leg. This will allow the old oil to drain. Slowly compress the fork over and over again until oil stops coming out. Reinstall the drain screw.

Use a vise to hold the bottom of the fork leg. In our case we used an 8mm Allen wrench, remove the bolt from the bottom of the fork. This will allow the damper rod to be removed in an upcoming step. If the bolt turns but does not loosen, have a helper turn the bolt while you compress the fork. This may help break the bolt loose. If it won't break loose, continue to disassemble the fork. We will later post information on how to make a tool to hold the damper rod.

Carefully remove the fork cap. It may be under tension, and the spring and a washer may try to jump out. Be prepared. Remove the washer and the spring, clean all the oil off them, and set them aside.

Remove the fork boot by sliding it up over the top of the fork leg. Now that the bolt has been removed from the bottom of the fork, the fork stanchion and damper rod can be slid up and out of the fork leg.

Next we'll remove and replace the fork seals, which sit in the upper part of the fork leg. Using a small-blade screwdriver or hook-shaped tool carefully remove the circlip in the top of the fork leg. The washer underneath it can now be removed.

Using a rag to protect the top edge of the fork leg, use a large-bladed screwdriver to carefully pry the seal out of the leg, slowly working your way a little bit at a time around the bottom of the seal with the screwdriver.

Once the seal is removed spray the inside of the fork leg out with brake parts cleaner over a drain pan. Next, set the new seal in the top of the fork leg. We used a bigger socket as a driver as it was the perfect size (the outer diameter of the socket was just smaller than the inside diameter of the fork leg). Use strong, sharp blows to drive the fork seal into the leg. Once it is fully seated into the leg, put the washer back on top of it and reinstall the circlip.

Lubricate the seal with some fork oil or grease and carefully reinstall the fork stanchion and damper rod back into the fork leg.

Reinstall the fork boot. Clean the spring, and put it back in the fork stanchion. Add the washer back at the top, with the flat side facing up, and reinstall the fork cap. Reinstall the Allen bolt at the bottom of the fork leg, using the damper rod tool if necessary, then stand the fork back up and take the cap off again.

Measure out your fork oil using a measuring cup with a good pour spout. Our forks called 136cc of oil. Hold the fork stanchion so it doesn't slide down into the leg. Add the oil to the fork. Replace the fork cap.

Spread the lower triple tree a bit with a large-blade screwdriver to make it easier to reinstall the fork leg. It only takes a little effort to spread it enough. Push the fork back up through the lower and top triple tree until the top edge of the fork stanchion (not the top of the fork cap) is level with the top edge of the top triple tree. The fork cap should sit just proud of the top of the bolts, but leave the lowers loose.

Repeat the last steps with the other fork leg. With both fork legs reinstalled, bolt the brake caliper back on, reinstall the fender, and install the wheel and speedodrive, being sure to line up the key on the speedometer drive to the inside of the fork leg. Take the motorcycle off the center stand and 'bounce' the front end to align the forks. Tighten the lower pinch bolts. That's it, you're ready to ride again...
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