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F-Twins Tech - F800GS Renewing Fork Seals


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The articles, posts and comments in this tech section are posted by individual members and reflect their personal thoughts and experiences with repairing, maintaining, and generally working on motorcycles. This information may require specific knowledge and skills, may or may not be correct or current to model.

The authors of information found here and the BMW MOA take no responsibility for ensuring the accuracy of any information (including procedures, techniques, parts numbers, torque values, tool usage, etc.), or further for any damage of any kind or injuries incurred or caused by anyone following the instructions or information found here.

It is the duty of the individual to either assume the liability himself for responsibly using the information found here, or to take the bike or accessory to a Dealer or other qualified professional service.

Please ensure you dispose of your used chemicals, oils and fuels in an environmentally responsible manner. Most Auto Parts stores and service stations will accept used oil and lubricants, tires and batteries, please check for your local availability. Here's a link where you can look up a place to dispose of your used fluids (oil, coolant, brake fluid, etc.) - http://earth911.com/

This article, text and photos are Copyright of the individual authors and the BMW MOA, any copying or redistributing is permitted only by prior written authorization.


Final note: The motorcycle's two wheels are the only thing keeping you upright. When in doubt, take your motorcycle to a reputable dealer.


Renewing the fork seals on your 2013 or later BMW F800GS

Fork oil is kept contained in the fork internals by a series of seals. Age, mileage, riding conditions, and previous maintenance (or lack thereof) all contribute to how long those seals keep the fork oil in the correct place.

It's generally accepted that you should not ride for long on a bike that has a leaking seal. Fork oil could easily contaminate your brake pads and disc surfaces, thereby reducing your stopping power. Different fork oil levels between the forks can cause an unbalanced ride and poor shock absorption. Finally, oil can attract more dirt and debris onto the sliding surfaces of the fork, causing what should be a relatively cheap fix (~$35 for the seals and ~$20 for fork oil) into a very expensive one (new forks sliders will run you $578.76 per side).

Note 1: The specific bike shown is a 2013 F800GS using WP Suspension forks (43 mm). Older bikes have a similar process, but use a different style of forks (Marzocchi - 45 mm).
Note 2: The tools and materials used are by personal choice and are not due to any affiliation with any brand

Supplies Required:
SAE 7.5 wt Fork Oil - we need about 1220 milliliters or 41 ounces (1.3 quarts)
New Fork oil seal and new dust seal (Part number as a set: 31 42 8 534 232)

Tools Required:
- 24mm socket (preferably 6-sided) (different size for bigger forks)
- T25 star (Torx) bit
- T30 star (Torx) bit
- T45 star (Torx) bit
- E12 external star (External Torx) socket
- 17mm socket
- 13mm open end wrench
- Ratchet(s) that fit the above
- Flat screwdriver or flat car plastic removal tools
- Fork seal driver of the correct size
- Torque wrench
- Suitable way to raise the front wheel and keep the bike steady
- Container to catch the used oil
- Your least favorite shirt/rag
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We will need to remove the front fender, brakes, and front wheel so we can remove the fork legs.

Start by removing the front fender. On each side of the fender, there are plastic pieces that hold the brake lines in the proper place. These are held in by plastic snaps, so gently pop each plastic piece out.

Remove the three T25 star (Torx) screws on both sides of the forks, as indicated by the green arrows.

Using your E12 external star (External Torx) socket, remove both bolts on each of the brake calipers, as indicated by the arrows

Note: the wheel and fender are still attached to the bike in this photo

Using your T25 star (Torx) bit, remove the brake line retainer on the throttle-side fork. This can be gently opened more to clear the fork leg for removal.

Remove both calipers from the fork legs and brake discs. Make sure to tie them up out of the way or place them on a suitable holding device to relieve any pressure on the brake lines.

Take a moment and clean the bottom, chrome portions of the fork tubes. Because we are going to slide the fork tubes all the way down to the axle holder, any dirt/bugs could effect the dust and oil seals. Five minutes of cleaning may prevent premature fork seal death, so it's worth it to make sure the sliders are clean.

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We are going to work on one fork leg at a time so we don't mix up parts between each fork leg.

Using your T45 star (Torx) bit, slacken the top clamping bolts (A and B as indicated by the green arrows)

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Using your 24mm socket, partially unscrew the top cap of the fork. Using a paper towel between your socket and the top cap will reduce the risk of marring the top cap.

We will now remove the fork leg from the bike. Using your T45, slacken the lower clamp bolts, as indicated by the green arrows. Make sure you have one hand holding on to the fork leg, as the fork could slip out of the triple tree.

We can now remove the top cover from the fork. Use your 24mm socket to unscrew the top cover all the way.

Then, using your 13mm open end wrench, and your 24mm socket, loosen the lock nut located on the underside of the top cover (indicated by the green arrow). You may need to spin the spring around a little bit to get a good grip on the lock nut with your wrench.

Here is the top cap off. Note that there are two spacers that are in the recess of the top cover; most of the time they seem to stay in the cover itself.

I don't believe the spring is wound progressively, but out of habit, I mark the top of the spring with a twist tie so I remember the spring's orientation.

We can now extract the spring from the fork leg. The spring will be coated in fork oil, so you may want to lay down a protective cover over your garage floor to ease cleanup.

We can now dump out the old fork oil into our suitable container. The plastic piston rod will extend as you tip the fork upside down, so be careful that you don't damage anything. We want to push in and draw out that plastic piston rod several times to expel all of the fork oil, so this may process may take some time.

Once all the oil is drained out, we want to remove the dust seal. I found a car plastic anchor remover tool was helpful in getting the dust seal to unseat from the fork recess. The biggest thing that you want to do when removing the seal is to take your time and not mar up the rather soft aluminum fork.

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Next, we'll want to remove the oil seal retaining ring. This is a snap ring that sits inside a groove machined into the fork that holds the oil seal in place. One end of the ring has a notch cut out, allowing us to "hook" a tool underneath it, and gently pry it out.

I chose to use the plastic anchor tool again as not to mar up any of the surfaces. If you need to use a metal tool (be it a screwdriver or a pick), then I would slide the fork tube up, wrap an area with electrical tape, and slide it back down near the oil seal. This will protect the fork tube from any errant damage.

This photo shows the retaining ring removed from above the oil seal.

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Now we will remove the oil seal. Make sure you eat some spinach Popeye, because we will forcefully pull the chrome fork tube away from the gold top tube. This will pop out the oil seal from it's recess in the fork.

This photo shows the oil seal removed from the fork tube, with a washer and two metal (one silver, one brown) bushings below it.

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Here's a picture of how all the pieces stack inside the fork.

Note: #1 is closest to where the tire is held on.

1: Dust seal
2: Oil seal retainer ring
3: Oil seal
4: Metal washer
5: Silver bushing
6: Brown/black bushing

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