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post #1 of 14 (permalink) Old Mar 23rd, 2008, 5:57 pm Thread Starter
 
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Fork Seals

Got only 30K on the clock and the fork seals are already leaking. The workshop manual says to use a special drift to drive home the seals. Is this absolutely necessary or can I just drift the new seal home with use of a socket like the rest of the sane world?

Sounds like I have aleady answered my own question but would like to hear any horror stories that may be out there to avoid wasting my time/doiing the job twice
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post #2 of 14 (permalink) Old Mar 23rd, 2008, 8:01 pm
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Quote:
Originally Posted by markpenman10
Got only 30K on the clock and the fork seals are already leaking. The workshop manual says to use a special drift to drive home the seals. Is this absolutely necessary or can I just drift the new seal home with use of a socket like the rest of the sane world?

Sounds like I have aleady answered my own question but would like to hear any horror stories that may be out there to avoid wasting my time/doiing the job twice
First, this is one of the easiest jobs you might have to do. Despite the convoluted procedure in the manual, you can actually replace the seals from the top starting, with the fork yolk. From memory you don't have to dismantle/remove the fork legs. After familiarising yourself it's probably 3/4hour the first leg and 1/2 hour the second. My bike is an older '97 with Showa seals. I noticed the BMW replacements now have a main sealing lip and an outer dust lip.

Old fork oil should be removed via the drain plug near the wheel spindle, I'd flush it through to get any particles out. There's been a lot of guessing as to what weight fork oil BMW used, since you can buy fork oil easily from most bike shops. There's no damping to be affected by oil weight so I think I chose 8 or 10 to keep the oil in. 5 weight is getting a bit thin. You should also check the polished chrome sliding surfaces very carefully for pits, 'dings' or stuck bugs. Polish with 1200 grade wet and dry, paint rubbing compound and or Jiff bath cleaner. Any problem with the chrome surface will knock out new seals very quickly.

I used a large socket I found to tap in the seals, but I did check with a depth vernier that it was as central as I could get it.

Putting the correct oil volumes back is important so measure the oil carefully into each leg. Over fill and you may risk pushing the seals out.

NB Oil in our fork legs is only there to oil the sliding bush, there is no shock absorber in the leg struts. In theory, a fork oil leak should not be an MOT fail unless it is pouring down over the brake disc.



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post #3 of 14 (permalink) Old Mar 23rd, 2008, 11:31 pm
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Just did my first set of fork seals on the bike, after four years and 75k miles. As vox says, it's an easy job. Details of the work are at: http://www.rhhall.smugmug.com/gallery/4566124_YkfYs

Here are some of the steps:

Strip the plastic and support the front end:


Remove the handlebar assembly and loosen the fork tube pinch bolt:


Carefully extract the fork tube, making sure you don't scratch it:


Pry out old upper seal:


This one is showing it's age:


Remove spring clip:


Pry out lower seal:


Clean seal area, lube new seal, and re-install with a seal tool or socket:


Install spring clip.
Inspect fork tube for any nicks, burrs, scratches:


Lubricate seal and install fork tube using a twisting motion, lube upper seal and install:


Install fork tube into triple tree, fill with fork oil to about five inches from top of fork tube.


Reinstall handlebar assembly, torque to specs:


Repeat for other side. Re-skin the bike and go for a test ride.

Sierra Cement: Good for skis, bad for knees.

www.rhhall.smugmug.com
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post #4 of 14 (permalink) Old Mar 24th, 2008, 6:16 am
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Hey Richard, the OP couldn't get better than this from a manual!

Nice presentation to have the key ops and linked photos.



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post #5 of 14 (permalink) Old Apr 8th, 2008, 9:56 pm
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Rich
Thanks for posting this. I'm out rolling around on the garage floor changing my fork seals (I removed the fork leg before I read this) and I am having a little trouble getting the inner seal out. I thought I would pop in and check the website before I applied brute force to it and broke something. This is much better than the shop manual, the pictures are a big help.
Thanks again
Quote:
Originally Posted by rhhall
Just did my first set of fork seals on the bike, after four years and 75k miles. As vox says, it's an easy job. Details of the work are at: http://www.rhhall.smugmug.com/gallery/4566124_YkfYs

Here are some of the steps:

Strip the plastic and support the front end:


Remove the handlebar assembly and loosen the fork tube pinch bolt:


Carefully extract the fork tube, making sure you don't scratch it:


Pry out old upper seal:


This one is showing it's age:


Remove spring clip:


Pry out lower seal:


Clean seal area, lube new seal, and re-install with a seal tool or socket:


Install spring clip.
Inspect fork tube for any nicks, burrs, scratches:


Lubricate seal and install fork tube using a twisting motion, lube upper seal and install:


Install fork tube into triple tree, fill with fork oil to about five inches from top of fork tube.


Reinstall handlebar assembly, torque to specs:


Repeat for other side. Re-skin the bike and go for a test ride.
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post #6 of 14 (permalink) Old Apr 27th, 2008, 2:12 pm Thread Starter
 
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Fork Seals

Fantastic; didn't realise/think about doing it from the top. I have done it from the bottom [a lot more work]. got my seals from a so called specialist and after a couple a days they were leaking. After investigating, turns out there are two distinct differences between rotary and reciprocating seals. DO NOT USE ROTARY SEALS.

As i'm a DIY enthousiast [deep pockets and short arms/squeek when walking], I couldn't resist trolling through the local bike shops instead of forking out 35 quid for a BM set [what a rip off].

So - Once upon a time, In the deep dark dusty depths of a medieval scooter shop basement I found GOLD.....

"VESRAH"

VESRAH of all people make the perfect seal for the K12. Although normally only made for Jap-Crap race machines they are a perfect size for the Marcozi shocks and of a much, much higher build/material quality with steel casing. Code is AR-3502 size is 35x47x10 and cost me a whopping 8. The only difference in size/shape is that they do not have the .5mm raised dust lip [why they have them in the first place is as queer as a bottle of chips cos they have a separate dust cover]

I have to say: comparing seals side by side, I will be amased if I ever need to replace these seals.

So here's to BMW for using absolute pants equipment.

But hey guys, just remember one thing BM might get it wrong from time to time but don't go Jap. Riding a jap bike is like bonking a pro; great ride - until somebody sees you with one
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post #7 of 14 (permalink) Old Apr 27th, 2008, 5:45 pm
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I did something similar after forking out several times for the crap OEM seals (BMW part number 31-42-2-333-409 Seal Repair Kit for Marzocchi @ $38CDN x 2!). I found Leak Proof seals for a KTM application that fit and are leak tight. Details: LeakProof seals, Motovan part #s 155-128 Fork Seal Kit, 36x57x10mm and 157-139 Dust Seal Only Kit KTM SX G5 02-07 (ref. Goallballs.com) @ $30CDN total.

Glen M.
'97 K12RS
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post #8 of 14 (permalink) Old Apr 28th, 2008, 11:28 am
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For most seals obtained from a bearing/seal supplier you just need the sizes (Oem parts list gives you that for most seals).

The dust lip is an option, so you're more likely to find a seal without than with. Yes the application is important (whether sliding or rotary shaft) and the pressure rating is on the damper (but not forks).

I put gaytors on my forks, so I'm not worried about bugs getting stuck to the slider and damaging the seal now.

Perhaps I'm fortunate in having a seal/bearing shop where I take a seal, tell them the application and they find me an alternative (but I always check the spec.). I've bought very few BMW seals and bearings. The needle bearings in the swingarm are dificult to second source, and if you aren't convinced about Teflon seals, most of the others are easily got in traditional format shape and not needing special sleeves to fit.

Do alternatives last as long? Well judging by the frequency with which certain seals (fitted by manufacturer and dealers) cause aggravation and need changing, replacement intervals in my humble opinion are down to the oem design and seal application, rather than the seal itself. So why spend $$'s at the stealer on oem stuff?



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post #9 of 14 (permalink) Old Apr 28th, 2008, 1:33 pm
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I replaced mine several years ago and the brand new ones leaked almost immediately. The BMWNA rep looked at the new and the old seals and could not explain why I had leak issues. As stated previously, the oil does no damping, just lubricates the fork legs. I ended up putting slightly less oil in each fork that the manual suggested and no leaks since 2001 and 50,000 miles!

RRG
98' Red Checkered
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post #10 of 14 (permalink) Old Apr 28th, 2008, 2:45 pm
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There is some back pressure equalisation going on and the less air space at the top, the more pressure will be on the seals before it equalises. I'm sure I thought about this at the time and looked for where the pressure would equalise. I may be wrong 'cos it's been all of 3 years now and no leaks, but I've a feeling there's a slot across the threads at the top where the cap goes on to let air in and out. If there isn't there should be something like that.



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