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Old 03-21-2014, 03:11 AM   #1
hurcomb OP
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Fork dust seal and oil seal replacement.

I'm installing some hyperpro fork springs and while I'm at it I will renew the fork seals.

Question: do I need to replace the dust seals as well as the oil seals?

I found a supplier on line who suggests that that the dust seals will outlast the oils seals many times over.

The bike is a 2009 and has don 40k Kms.
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Old 03-21-2014, 07:11 AM   #2
Moto Mikey
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Quote:
Originally Posted by hurcomb View Post
I'm installing some hyperpro fork springs and while I'm at it I will renew the fork seals.

Question: do I need to replace the dust seals as well as the oil seals?

I found a supplier on line who suggests that that the dust seals will outlast the oils seals many times over.

The bike is a 2009 and has don 40k Kms.
I replaced my fork seals while installing a pair of hyperpro fork springs too.. My recommendation is to replace both dust and oil seals since the entire assembly has to come apart anyways.. no sense being cheap over an extra $30.. especially if your forks start to leak in another 10k Kms since the original dust seals weren't doing their job and cause you to remove the entire assemblies again.

Not sure what brand you're going to get but I recommend the SKF seals. They are half the price of the BMW parts. Do NOT get the Racetech seals; they do not fit correctly.. about .5mm too loose.

SKF: http://www.dualsportarmory.com/skf-fork-seals/

Some pics and info on my blog if you need any help:
http://moto-mikey.com/2013/02/moto-m...ance-and-mods/
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Old 03-21-2014, 08:51 AM   #3
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Unless you don't care about suspension performance, with 40k on it I would give the forks a full service with fresh oil, seals, wipers and check the bushings for wear.
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Old 03-21-2014, 05:32 PM   #4
hurcomb OP
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Tar

Thanks for the replies. Yeah.. that makes sense to do them both while the forks are ripped apart.

And cheers for the SKF supplier link. I could only find the Athena and Kyoto ones previously which did not include the dust seals.
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Old 03-22-2014, 05:20 PM   #5
CaliKarl
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Couple of questions that arose while completing this job:

1. The bottom of one of the fork tube lowers is not smooth (i.e. if you bottom out there is a not-so flat area that the seals will hit). Should I take this to the dealer and see if my warranty will buy me another one? With the fork off, one cannot lift the upper off the lower smoothly like you can with the other for leg. The bike clearly came this way from the factory.

2. Both bushings have little grooves in the same place. Should I replace them?

Thanks!
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Old 03-23-2014, 02:07 PM   #6
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Quote:
Originally Posted by CaliKarl View Post
Couple of questions that arose while completing this job:

1. The bottom of one of the fork tube lowers is not smooth (i.e. if you bottom out there is a not-so flat area that the seals will hit). Should I take this to the dealer and see if my warranty will buy me another one? With the fork off, one cannot lift the upper off the lower smoothly like you can with the other for leg. The bike clearly came this way from the factory.

2. Both bushings have little grooves in the same place. Should I replace them?

Thanks!
1. Does anybody else have a fork tube lower that is anything but smooth near the bottom of the stroke?

2. Replaced with new ones.

Thanks for your replies!
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Old 03-23-2014, 02:38 PM   #7
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Originally Posted by CaliKarl View Post
1. Does anybody else have a fork tube lower that is anything but smooth near the bottom of the stroke?
I'm trying to figure out what you mean? Pics? Are you saying the chrome is damaged? The upper stanchion will not hit the lower leg on bottom out. The damper is your internal stops. Put it together without the spring and bottom it out to answer your question.
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Old 03-23-2014, 03:08 PM   #8
CaliKarl
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Originally Posted by Reaver View Post
I'm trying to figure out what you mean? Pics? Are you saying the chrome is damaged? The upper stanchion will not hit the lower leg on bottom out. The damper is your internal stops. Put it together without the spring and bottom it out to answer your question.
Chrome is damaged at the very bottom of the lower (must have always been as such). So when it 'bottoms out,' the upper stanchion, and the dust seal, does not bounce off the bottom of the lower?

Thanks Reaver!
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Old 03-23-2014, 03:50 PM   #9
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On my recent 800 fork build I found a rock had lodged between the chrome and plastic fender at the bottom. I did the same, built the fork without the spring and bottomed it out showing the damaged chrome is still outside. No, the dust seal stops about an inch short of the the lower leg.

Smooth the chrome with sandpaper to take away the sharp edges. I forget the amount of chrome showing at bottom out but you can place a zip tie on the chrome then go riding. See how low the zip tie goes and that should confirm it.
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Reaver screwed with this post 03-23-2014 at 04:03 PM
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Old 03-23-2014, 04:23 PM   #10
CaliKarl
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Originally Posted by Reaver View Post
On my recent 800 fork build I found a rock had lodged between the chrome and plastic fender at the bottom. I did the same, built the fork without the spring and bottomed it out showing the damaged chrome is still outside. No, the dust seal stops about an inch short of the the lower leg.

Smooth the chrome with sandpaper to take away the sharp edges. I forget the amount of chrome showing at bottom out but you can place a zip tie on the chrome then go riding. See how low the zip tie goes and that should confirm it.
Unfortunate that the fork lower would not be smooth as a result of bad casting (metal is 'bubbly' looking; quite thick). I always thought bottoming out meant the upper stanchion rammed into the bottom; rather, the cartridge hit bottom.

Thanks again Reaver!
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Old 03-23-2014, 04:41 PM   #11
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Originally Posted by CaliKarl View Post
Unfortunate that the fork lower would not be smooth as a result of bad casting (metal is 'bubbly' looking; quite thick). I always thought bottoming out meant the upper stanchion rammed into the bottom; rather, the cartridge hit bottom.

Thanks again Reaver!
If your chome is "bubbly" then it's rusty underneath. Bad processing. It you've got warranty then DON'T touch it! Show the Dealer and get it replaced.

The PRIMARY stops in the forks are the cartridge internals. If that fails, the SECONDARY stops are the upper tube hitting the lower fork ends. Uh, that would be a BAD day.
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Old 03-23-2014, 05:56 PM   #12
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rust

Just fitted hagon springs to my 2009 F800gs. I did the seals and steering head bearings while I had it apart.
On the front at the bottom of both forks was a very small amount of rusty pitting. It looks to be the small part of the fork not protected by the wheel/fork guard. So it is likely it has been hit by small stones.

I cleaned it up with emery paper and then put some clear nail varnish on it. (Any clear lacquer would probably do) It is below the full travel of the seals so not an issue.
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Old 03-23-2014, 06:23 PM   #13
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It looks to be the small part of the fork not protected by the wheel/fork guard. So it is likely it has been hit by small stones.
During normal operation, a thin film of oil is left on the porous chrome to help lubricate and protect. That bottom portion of chrome never sees the inside of the oil filled fork so it dries out and can rust. On aircraft we have to "oil" that bottom part every 3 days.
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