Howto: Replacing fork seals

[kapiteinkoek]

I find the fork seal howto's on this board mediocre at best so here you have the translation of my Dutch GS500 fork seal howto. I find that a howto for beginners cannot have too many pictures.

BTW is it not a good idea to put both threads (also the valve adjustment howto linked below) in the FAQ section?



Dutch version

In the same series: Valve adjustment with a lot of pictures




You need to replace the fork seals when they leak. Leaking seals will allow oil to escape from the fork which reduces damping and behaviour of the bike. It leads to poorer handling and you risk getting oil on the front brake which can be disastrous. At some point it will be a life threatening situation so you must intervene.

Current state of my GS500 front fork:





I have fork protectors because it is the best protection against rocks and other stuff. They are not pretty but ensure longevity of the chrome. As you can see the protectors are dried out and ripped. Next to this everything is greasy including the brake caliper mounts. I waited a long time before replacing the seals and as you can see the oil almost reached the brake rotor and pads.

Step 1 is getting new parts. You will need new seals and dust seals, fork oil and two new little gasket rings for the bolts in the bottom of the dampers. You may be needing new slide rings. I also advise you to replace the o-rings on the fork caps. Standard fork oil is 10W. As the stock GS500 forks are a bit soft you could choose to put in 15W oil instead.

It is time to start. Remove the steer first




Loosen the upper clamp


Now you can loosen the cap. NOTE: do not remove the cap but simply loosen them so you can easily remove them later. I have oldskool flat caps, I reckon most of you will have adjustable caps so you need to use a different tool (socket or key) to loosen them.


Now it is time to remove the wheel and the brake caliper. Do not let the caliper hang on the brake line but hang it to the frame with a rope.




As you can see I made a stand on which I can put the bike. It's a simple unit and very strong.

Remove the fender. PROTIP: Replace the original spherical head hex bolts with a different type. The original bolt heads are easily destroyed making them hard to remove.



Clean up for a bit because it will save you very dirty hands later.

Now loosen the lower clamps


If you have loosened these you can move out the dampers. This can take some effort, it may help to open the clamps up with a flat screwdriver. Try rotating the damper as well. You can add some penetrating oil but don't forget to clean that from both the dampers and the clamps.



By the way the black stuff on the dampers is some anti rust material so don't mind that.

Another picture of where the oil got


Once again do not postpone this maintenance for too long.

It can be handy to have something like this or a bench vise but you can do without it don't worry.


One of the dampers has a spacer in it so remove the bolt and tap it out



Now comes the biggest challenge, removing the bottom bolt


If you are lucky you can remove it just like that. NOTE: There may be a little bit of pressurized oil directly underneath the bolt. Wrap some cloth around the bottom to avoid it spraying everywhere. If you can't get it loose; Don't worry keep reading!


Now remove the cap and empty the damper. The cap has some pressure on it because of the spring inside. It's not that much but hold on to your tool. If it scares you put a towel over it that will be enough to stop things from flying everywhere in case you let it slip.




Run the oil out of the damper. It may be handy to keep the spring and stuff inside the fork for a bit so you can look at the way the parts are put inside. Mind the order of parts coming out. If you failed to check or remember it simply look at this drawing


Order of parts from top to bottom:
- cap
- spacer
- spring seat (which is a ring)
- spring

I have a '96 model, your damper may be a bit different such as this one


Or one of the newer models


You might find some other parts inside, maybe somebody upgraded the stock springs like I did. I don't have spacers or a spring seat, only the spring.

But wait, I could not remove the bolt at the bottom of the damper, what do I do now? The reason you cannot remove the bolt is because the piston inside will rotate with it. It is this thing:


There are different ways to remove it such as using an impact wrench. Not everybody has one or wants to buy it but there are other tricks too. The inside of the piston happens to have the same shape as a bolt that fits in a size 24 socket:



If you put the bolt on a stick you can put it inside the damper and stop the piston from turning. I made a stick from some central heating pipe and a little bolt:



I cut it in for a bit with an angle grinder and put some tape around it for a snug fit.


You could also use a threaded rod and simply put 2 nuts tight together on one end. Anything that looks like this will do really.

Once it's done leaking the last oil out of it you can put it on your stick and remove the bolt


Don't forget to remove the little ring


Lift the damper and there we go



Now let's pull everything apart. Remove dustcaps:


You can now see the oil seal


Remove the clip



Take the lower part in one hand and the chrome top part in the other and simply rip them apart. Or just clamp it into your thing and pull out the top.



NOTE: Do not throw away the old fork seals yet!

Now we inspect:


There are 2 sliding rings on the inner leg. A short ring and a wide ring at the bottom. Check the outside of the wide ring and the inside of the short ring. The rings are made of metal with a copper and teflon coating. Look closely at the wide ring at the bottom, you can see the copper through the teflon layer. This one is wearing out so we have to replace it!

The short rings look fine. There is a nice non-transparent layer of teflon on it.


Compare the new and old ring. New on top, old one below it.


What if they are worn out but you don't replace them? The inside of the damper will start to wear out, leading to play on the leg, screwing up your new fork seals and making them leak soon again.

Now clean the parts and maybe polish the chrome parts with some chrome stuff. Polish away rust if there is any. You can also use some very fine sanding paper to remove rust.


new and clean stuff


Now we start rebuilding. It's like taking things apart but in reverse order. Put a bit of fork oil on the new seals before putting them on the legs.


Put back in the piston


Everything back together



You will probably notice that the new fork seal does not want to go in all the way. There are different ways to get this done such as a fork seal driver:


You could also use a pipe that fits around the inner leg. If you don't have any of these things, take the old fork seals and put them on top of the new ones. Now you can use a piece of wood and a hammer to drive the new seals into the leg without damaging them because you are hitting the old seal on top. I used to do it like this before somebody gave me the fork seal driver for free.

Once you have pushed the seal low enough you can reinstall the clip:


Add a new dust seal


Insert the bottom bolt, don't forget the little gasket ring. You may want to use the tool again to stop the piston from turning inside.


Now put the damper straight up again and fill it with oil. You fill the damper while it is compressed, but without content (don't put in the spring and spacers etc in yet). If you have stock springs fill up the damper up to 99mm under the edge. If you have these full size springs like I do, fill up to 140mm under the edge. Don't go to fancy on the millimetres, a couple more or less won't harm anyone.

I fill up the damper too much and remove the excessive oil with a marked syringe.



NOTE: There is still air trapped in the bottom of the damper. Fill up the damper, take the inner leg and pump it up and down a couple of times to get the air out. Only after you did this you should start measuring the oil level.


Now put the contents back into the damper. Extend the inner leg first else the oil may run over the top


I kinda installed my spring upside down but it doesn't matter much really

I strongly recommend putting a new o-ring on the cap


Your current ring will most likely be old and may start to leak after putting it back. You will have oil all over your steer. Size of the ring is about 29mm inner diameter and a thickness of 3mm, maximally 3,5mm.

There is no need to really tighten the caps yet. You can do this later.

All together you have a nice set of legs again


Put them back on the bike


Not everybody likes these fork protectors but it is most definitely a good idea to put on some additional protection. The newer GS500 models have little caps near the seal


Originals are rather expensive but you can find these aftermarket fork protectors eveywhere. I recommend to put these on if you don't have them yet. It protects the most important part of the inner leg from road debris.


Now tighten the bottom clamps first



Now tighten the caps!


Now tighten the top clamps


Add the thing in between


NOTE: Do not tighten these bolts yet

Add the fender


Put the spacer in the bottom


NOTE: Do not tighten this spacer bolt yet. You need to do this later to avoid unwanted tension


Put in the wheel and tighten it


You don't really need a torque wrench but it is handy certainly because of its size

Now tighten the little bolt


Finally you tighten the thingy bolts



There you go, you have replaced your fork seals. Oh, don't forget to put back on your brake caliper as you might need it.

[Endopotential]

Awesome write-up, thanks so much for posting!  Great photos to accompany the instructions.
Where were you 3 weeks ago when I was struggling with my fork rebuild? 

This should definitely be sticky'd to the FAQ instructions section.

FYI, for 2004+ model forks you'll need a slightly different tool to get the damper out.  A shaved down broomstick did the trick for me.

http://gstwins.com/gsboard/index.php?topic=70830.msg851134#msg851134

[kapiteinkoek]

Increase broomstick grip by covering it with the inner tube of a bicycle tyre

[Carltheproducer]

Awesome write-up, thanks so much for posting!  Great photos to accompany the instructions.
Where were you 3 weeks ago when I was struggling with my fork rebuild? 

This should definitely be sticky'd to the FAQ instructions section.

FYI, for 2004+ model forks you'll need a slightly different tool to get the damper out.  A shaved down broomstick did the trick for me.

http://gstwins.com/gsboard/index.php?topic=70830.msg851134#msg851134

Please read my thread to see the quickest way to break the damper rod bolt from nut inside forks. http://gstwins.com/gsboard/index.php?topic=72508.0