Changing Fork Seals
Bike: 1996 Suzuki GS500E
Note: The fork seals of this type are called damper rod forks. They are common on older motorcycles and modern non-sportbikes. Modern sportbikes have what's called cartridge forks, which are a little bit different in their construction, but the basics of this job remain the same. The only other major difference one may encounter is working with upside down forks. Again, the main principles are the same, but certainly consult your manual no matter what type of bike you're working on.
The following instructions assume that the bike is secure with the front wheel off the ground, the wheel has been removed, the brake caliper is zip-tied to the frame, and other assemblies connected to the fork tubes have been freed from them.
1. Loosen triple clamp pinch bolts.
The forks on this particular bike do not have drain bolts on the bottom like most other bikes. In order for us to proceed, we'll have to drain the forks through the top. Therefore we'll first concentrate on draining them by taking off the caps even though we'll need to partially assemble them again in step 6 to loosen the damper rod bolt.
2. Loosen the fork cap and slide the fork out of the triple clamp.
3. Remove the fork cap.
Be careful when the cap reaches the end of the thread -- the spring is still partially loaded. Put a bit of pressure on the cap to prevent it and other bits from getting thrown by the spring.
4. Drain the fork oil.
Try not to let anything fall out of the fork by holding the spacer in. Be ready to fish stuff out of the drain pan, so start with a clean empty one.
5. Put the cap on.
We're just trying to put some pressure on the damper rod to loosen the damper rod bolt, so screwing the cap all the way is not necessary -- just catch a few threads and make sure it's not cross-threaded.
6. Unscrew the damper rod bolt.
This is the part that gets a lot of people. To get to the damper rod, one usually needs a long allen wrench. The manual usually tells you to get a special damper rod holding tool. 99.9% of the time, this is not necessary and one can either loosen it with a standard allen wrench or using air tools. The idea here is to be able to loosen the damper rod bolt without letting the damper rod spin inside the fork, which it wants to do, assisted by the fact that the internals are still coated with fork oil. If you don't have any kind of air tools, a basic 3 gallon compressor can easily be found used online. After that, air tools themselves are quite affordable and are a good investment. If you find yourself using an air wrench, you'll be using a socket and will need to get a straight piece of an allen wrench. Those wrenches usually come L-shaped, so you'll have to cut a piece of one, long enough to stick out from the fork leg. Then you'll be able to put an appropriate size socket on it and of course it'll be ready for an air wrench. Sometimes hardware stores sell some premade allen sockets like this, but I've never seen one that had a long enough allen piece that would do the job here. Secure the fork leg. If you're using a vice, be sure to use wooden chucks to avoid metal-on-metal contact with the vice.
7. Open the cap and remove all internals.
8. Make sure the damper rod comes out.
9. Remove the dust seal.
10. Remove the stopper ring.
Use a #1 flat-head to pop out the stopper ring. Be careful not to scratch the inner tube.
11. Separate the tubes.
This step may require a bit of force. Hold the outer tube with one hand and the inner tube with the other and slide them apart until it stops with some force. The thing stopping the movement at this point is the fork seal itself. After a few whacks, the tubes should separate with the fork seal caught on the inner tube. Inspect the Teflon coating on the bushings. The upper bushing has its coating on the inside, so you will want to pop it off the tube to be able to inspect it. Put new ones on if the coating is damaged or worn through.
12. Replace the seal on the inner tube.
Slide the old seal off the tube. Before putting the new one on, coat its inside surface with some fork oil. Seals are directional, so check with the manual to make sure you're installing it the right way.
13. Put the damper rod back in.
Make sure you're not missing any parts on the damper rod, such as the rebound spring. Slide it into the inner tube and make sure it's sticking out of the other end.
14. Install the damper rod bolt.
You may have to put in enough fork internals to be able to apply a bit of pressure on the damper rod. This can be a pain, but you have to make sure the damper rod bolt has caught a few threads and is holding the damper rod by trying to separate the fork tubes again. If you feel something stopping the separation, the damper rod bolt has caught.
15. Pre-seat the fork seal with your hands.
Try to get the top of the fork seal to be flush or below the outer fork tube edge.
16. Seat the fork seal with a PVC tube.
Here's another part where the manual says to get a special tool. They usually recommend a tool called a fork seal driver, which is nothing more than a metal piece of tubing whose inner diameter is a bit larger than the inner tube and the outer diameter a bit smaller than the outer tube. You then use the driver sort of like a hammer to drive the seal into its place. The same can be done with a piece of PVC tubing of the same inner and outer diameters, long enough to clear the top of the inner tube. A mallet is then used to drive the seal in its place. If you're cutting a PVC tube down to size, be sure to cut at a 90 degree angle so to apply equal pressure all around the seal and drive down uniformly. Still, occasionally twisting the PVC tube is recommended.
17. Make sure the seal is seated properly with the stopper ring groove showing completely.
18. Install the stopper ring and the dust seal.
Make sure the stopper ring fits completely into its groove. If it doesn't, the oil seal may have to be driven in a bit more.
19. Torque the damper rod bolt to spec.
You may need to put the spring, spacer and cap back on just for this one to apply sufficient pressure on the damper rod to prevent it from spinning. Do not use the air wrench!
20. Fill the fork with oil.
Take the cap off again (I know, I know) and take out the spring and spacer (check with manual for appropriate parts to be installed during fork oil level check). Compress the fork all the way. Fill the fork with appropriate fork oil up to about an inch and a half from the top. Compress and expand the fork a few times to let the oil fill the space on the other side of the damper rod.
21. Set the oil level.
Make sure the fork oil is at the specified level. The level is normally measured from the top. It is recommended that it be set by siphoning out the excess using a fork oil level tool. It can be purchased at most bike shops. It works by setting the length of a tube sticking out past a stopper to be the oil level specified in the manual. The tube is then put on the fork tube with the stopper flush with the top of the fork tube. The tool's tube is connected to a syringe that is used in reverse to suck out the fork oil through the tube until the level gets down to the set number.
22. Install the fork cap.
Torque down the fork cap to the specification and complete installation of the fork tube on the motorcycle in accordance with the manual.
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