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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 Oil

CX500Z, A, B 1978, 1979; CX500C, D 1979, 1980 : 135 cc in each fork leg. CX500 C 1981, 1982 : 220 cc in each fork leg. CX500 D 1981 : 185 cc in each fork leg. CX500 EC (Eurosport) : 265 cc left leg and 250cc in the right leg. All GL500, GL500D and GL500I : 210 cc in each fork leg. CX650C : 480 cc in each fork leg. CX650 E-D (Eurosport): 290 cc left leg and 275 cc right leg. GL650, GL650D2-E, GL650I : 275 cc in each fork leg.

    • A method of replacing the top caps of the forks with common tools. By DanCX500

Replacing the top caps on forks can be difficult being that there is the spring force to have to push the cap down and turn it at the same time. The pictures below show using an 1 1/8" socket with a long extension to aid in this task. The fork tube was lowered down in the triple tree because the handle bars interfered with the socket in the correct location. The socket gripped the cap just enough to be able to turn it to get the threads started. The extension was turned by hand. The cap was tightened with a 17mm open end wrench. The triple tree works well holding the fork tube without damaging it as a common vice would. 800x600px 800x600px

    • An Alternative to Replacing the Fork Seals:

This has been around for awhile and may be worth a try before replacing the seals. I have not tried it, but the following post from the Forum gives the process some hope.

Sealmate is a tool that can fix your leaking fork seals without removing or disassembling your forks. This tool works great, it can prevent you from having to replace your fork seals which can take a lot of time to repair, and cost a lot of money.

You can easily get debris in your seals, which causes them to leak while riding and this Seal Mate tool can be thrown in your backpack to have quick easy access to removing and cleaning the the debris from the fork seals while out riding.

Never let leaky fork seals ruin your day of riding again! This product works on almost any type of motorcycle. Before you try to go through the hassle of repairing a leaking seal give the inexpensive tool, Seal Mate a try today.

Below is an instructional video on how the tool works.

Link to Video

    • Satisfaction is guaranteed: We are so confident that you will be fully satisfied with your purchase of this tool that if for any reason you are not completely satisfied with this product than we will give a full money back guarantee if returned within 14 days!

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Senpro's Post:

You could try one of these.

They claim 95% of leaky fork seals is due to dirt.

I haven't tried one yet but my 32 year old fork seals were leaking and I cleaned them during a fork oil upgrade. That was a few weeks ago and still no leaks. That 95% claim might be true.

Shep's reply: A couple of members on here have used the SealMates with success smile.gif

However I think they bought a spare as a back up as they can be sort of disposable.

I've thought I could most likely make one out of a thin bit of plastic milk container?

Another old,"Trials Rider" I chatted too said they use a bit of PVC tape around the fork tube and and pump the fork to clear the seals as it's a common problem for them getting grit into the seals even with dust covers.I've never tried this so cannot say if it works.

Sniperdoc's post:

I decided to fab the tool up myself. I first tried plastic from a cat litter carton; it was too thick to get into the seal. Next, I tried plastic cut from a plastic orange juice jug; it was too thick. Lastly, I tried plastic cut from a 2 liter ginger ale bottle; it was the perfect thickness for the job.

I will try the results tonight with a road test.

I am ordering OEM fork seals from Discount Honda Parts. At $7.88 each, the price is not too bad, besides I need a few other OEM parts anyway.

I will report back later with results from the home-made tool.

No leak ... after using the home-made fork seal cleaning tool and 25 miles later. We shall see how long this quick fix lasts.

I just got back from 35 miles or hard riding on the most bumpy and twisty roads I have available. There is not any indication of a fork seal leak whatsoever. The tubes are bone dry. I think there is something to this.

Below is a picture of the tool I made from a 2 liter ginger ale bottle as described in a previous post.

Resized to 39% (was 1024 x 768) - Click image to enlarge IMG_20120523_223929-1.jpg

I watched the video in the link Senpro provided which gave good directions on how to use it.

What I did was:

  • Pry up the dust boot gently with a putty knife
  • Hold the plastic against the fork tube
  • Work the hook end down inside the seal
  • Pull up to hook the bottom of the seal inside the slider
  • Work the tool all the way around the seal a couple of times
  • Rotate the tool back to withdraw it from the seal
  • Straddle the motorcycle and pump the forks up and down multiple times
  • Wipe the oil and dirt off the tube
  • Repeat the pumping and wiping until there is no more fork oil coming out (it took twice for me)

It seems to be a quick and easy fix! (at least so far)

Here is a thread from the old forum on replacing fork seals: Thanks to Abes_CW for the information.

^ spacer.gif 2nd question first, yes fork oil can leak out from the around the bottom bolts. At the bottom of the fork is an Allen bolt, 6mm. The manual recommends using a locking agent on it, most here don't recommend it. When I did my seals last year I reinstalled without agent, and one was fine, the other did a very slow drip. I'd get two or three spots worth overnight. I redid them again last weekend (one had no leak on the bottom but the seal didn't seat first time, the other seal was fine but was leaking at the bolt), and when I reinstalled I used some anaerobic gasket sealant on the threads of the bolt in lieu of a locktite. A week on and 500km later, no leak, and it shouldn't be too difficult to break free for the next time.

I'd say about 2-3 hours for the change. On mine, the most time was spent on dis assembly, not actually changing the seal. You don't have to remove fairings et al to get to your triple so it should be pretty simple. Rob Davis' page is excellent for instructions. Be prepared for difficulty in removing the allen bolts. An impact driver may be required. Nothing worse than having it all torn apart and realizing you don't have the right tool to finish the job. Center stand, jack under the engine to get the front wheel off the ground. I use a short length of 2x8 lumber between the jack and the engine to evenly distribute the weight. Remove your brake caliper, and bungee it back so it doesn't hang free. Remove the speedo cable. Take off those 1/2 moon thingies. Mine were marked with punch dots to show which was which, right fork 2 dots, left 1, with dots on both the fork and bracket. Your wheel should drop out. My GL I had to deflate my tire to clear the fender. Remove fender. Remove air balancer crossover hose if you have the air suspension (it's at the top of the forks) Loosen the spring cap at the top of the fork. Don't remove it, just break it free. The triple will act as a vise to help with this, you want to try to avoid using a vise on the fork tubes when off the bike. (or be careful, use soft jaws)


Loosen the upper and lower pinch bolts on the triple tree on each side. You may want to note your fork position in the triple, so when you put 'er back together you have the same ride height if desired. The forks should drop out the bottom of the tree. Remove the fork cap, carefully as it is spring loaded and under pressure. You don't want it hitting you in the eye or have pieces inside fly to the mystery places where they will never be found. I think it is the same place odd socks go from the dryer. Press down as you loosen!


Notice I use a rag to assist, same goes for reinstall, saves your hands big time. (04/09 edit)

After the cap is off, you will find a short spring, a spacer (washer type thing), and a long spring. Note the orientation of the spring coils they will be tighter on one end, for later reinstalation. Remove these. They will have gross grey oil on them with a pudding consistency likely! Wipe them clean. Pump the fork a few times to get as much gunk out as you can. I left mine inverted for 1/2 hour to drip out.


So far so good. Remove the allen bolt at the bottom. Don't strip it! Use the right tool. (6mm alan wrench) If you are holding the fork upside down, when the bolt comes out a piston with the rebound spring will fall out. Note the orientation for reinstallation.


Remove the dust cap, carefully prise up with a flat screw driver.


There you will find the dreaded circlip/snap ring. This to me was the biggest PITA. Again having the right tool makes this short work.


With the circlip out, IIRC there is another bushing to remove. grab the slider with one hand, the fork lower in the other, compress then rapidly extend them. This will pop your old seal out, and the slider will come free for cleaning. Note the condition of the fork slider bushing, it's a 2" collar at the end. If it's excessively worn it should also be replaced (copper surface showing over 3/4 of it, it normally has a teflon type surface).


all the parts lined up.

With everything clean, it's time to put back together. Position the new seal, with the numbers facing up, centre it in place. Guys here bought a 1 1/2 inch pvc pipe fitting to place over the seal to tap on to drive the seal. I positioned my old seal on top of the bushing on top of the new and used that to drive it down. Worked great. You have to get it down far enough so the grove the circlip/snap ring fits in is exposed.


Circlip/snap ring in, seated in it's groove and your ready to reassemble! Dust cap on, Piston with rebound spring in, put some sealant on the allen bolt and reinstall and tighten. It won't thread in unless you have the fork in an extended position. Drop in the large spring, spacer and top spring. accurately measure the correct amount of fork oil for your model (listed on Rob's page). You need the same amount for both forks. If you spill some out you'll have to empty and start again to ensure they are balanced. Extend the fork, take the top cap, I use a rag between it and my hand, and compress the springs down to tighten the cap in. I put the fork lower between my feet, hold up the slider with my left hand and push down, turn in with my right. Left hand keeps the fork extended so you don't have to compress the springs far to install the cap, much easier! Your fork is now together, repeat and rinse with the other, and put 'em back on the bike! Note the line at the top of the fork. For the GL, this line goes at the top of the top clamp in the triple. You can push them up farther to lower the front end, make sure both forks are the same height.

Don't do them both simultaneously, so you have a complete one as a reference if you forget where all the bits went. I am not a great mechanic, with you dad helping you it should be a piece of cake. If I can do it anyone can (of course I had to do it twice.... emotion-5.gif

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