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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: frankenduck on September 07, 2011, 07:00:06 PM

Title: Fork Maintenance
Post by: frankenduck on September 07, 2011, 07:00:06 PM: Draining forks: Be sure to put some aluminum foil over the rotor, wheel and tire below the drain hole before removing the drain plug. When you put the drain plug back DO NOT OVERTIGHTEN IT. The threads in the fork lower strip fairly easily. Just get it nice and snug so it doesn't leak or fall out.

Fork Oil: I use Honda SS-8 10W fork oil with good results. Note that fork oil weights are not standardized so 10W from one manufacturer may not be the same as 10W from another manufacture. For example, if you look in the BMW approved fork oils in the K75 Rider's Manual you'll see a whole slew of numbers and weights:

see k75forkoils.jpg below..

Fork Oil Quantities: Brian Curry did a nice write-up on this topic over at IBMWR: http://www.ibmwr.org/ktech/fork-oil.shtml (http://www.ibmwr.org/ktech/fork-oil.shtml)

Attached to this thread are PDFs of the fork portion of the 1988 Haynes Manual for K75s and K100s as well as the Clymer Manual fork portion for 4V K bikes.

edit by scott_ 10-13-13 to update missing photo
Title: Re: Fork Maintenance
Post by: billday on January 03, 2012, 05:08:46 PM: Drake,

Thanks for this useful info, I will be doing some fork maintenance this winter.

The link to the Haynes gets me a 404 error message, can you check?

Regards

Bill
Title: Re: Fork Maintenance
Post by: frankenduck on January 03, 2012, 05:23:02 PM: Quote from: billday on January 03, 2012, 05:08:46 PM
frankenduck,

Thanks for this useful info, I will be doing some fork maintenance this winter.

The link to the Haynes gets me a 404 error message, can you check?

Regards

Bill

Some attachments got blown away when I upgraded our forum software. Thanks for the heads up. I'll reload those in a few minutes.

UPDATE: I have reloaded those attachments so they should work now.
Title: Re: Fork Maintenance
Post by: Wescoe on January 08, 2012, 04:03:52 AM: Well I blew a fork seal today. Looks like I'll be replacing both while its apart, obviously replacing the fluid as well. Pondering progressieve springs (Works performance) and Rancho boots in place of BMW gaiters. Thoughts?

Anything to look out for or is it a pretty straightforward fork seal replacement? I've never done it on my '94 K1100RS.
Title: Re: Fork Maintenance
Post by: mystic red on January 08, 2012, 07:45:51 AM: All sounds good to me. As for seal replacement, it is straight forward until you hit the little retaining clip. Seems everyone has a different way of getting them out. Just don't get frustrated and scratch things up. #2 in the fiche.

(http://www.maxbmwmotorcycles.com/fiche/DiagramsMid/B0000626.png?v=03252011)

I like my Works springs. And I ran gaiters for a few years with no seal problems, took them off for a summer and had to do the seals again. So back on they went.
Title: Re: Fork Maintenance
Post by: Scott_ on January 08, 2012, 08:41:53 AM: I've got seals ordered. They have come down in price.... $17.50 ea from Max's.
Only to now find them direct from Marzocchi(part #528134) for half that. €5.95 converted to us $ is around $7.50
But then there is the international shipping $ to add to the Marzocchi price too.

http://www.marzocchi.co.uk/moto/528134.html (http://www.marzocchi.co.uk/moto/528134.html)
Title: Re: Fork Maintenance
Post by: frankenduck on January 08, 2012, 12:35:07 PM: The stock springs on a K1100 are progressively wound. The Works springs "crossover" from a softer spring to a stiffer spring beyond a certain point of compression.
Title: Re: Fork Maintenance
Post by: billday on January 08, 2012, 04:10:45 PM: Quote
UPDATE: I have reloaded those attachments so they should work now.

Am I the only one having this problem? When I click on the links I don't get a .pdf, I get a link to a blank page and a prompt to save or open a .php file. Shouldn't the link just open a .pdf? Thanks, Bill
Title: Re: Fork Maintenance
Post by: Scott_ on January 08, 2012, 04:16:18 PM: Could be your application you are using.
I'm using IE8, and am able to download or open both files.
Title: Re: Fork Maintenance
Post by: Wescoe on January 10, 2012, 09:24:28 PM: OK so after further reading, seems my dust seals (rubber parts visible from the outside) are not cracked but oil is seeping past the dust seal on the left side. This means I have an issue with the "gasket," part #3 in the microfiche, correct? I have also read that part #5 can be damaged too. This is a new bike to me so when I take the for legs apart, I'm not sure what I'm going to find.

So looks like I need to order part 3 in the fiche, BMW part #31422312928 correct? Dust seals only need to be replaced if they are visibly damaged, correct?
Title: Re: Fork Maintenance
Post by: mystic red on January 10, 2012, 09:42:01 PM: 1, 3, and 5. Dust seal is how old? It's the last line of defense for the seals. Gaiters are the first. When you get those things all tore apart, you'll think, Shit, for 50 more dollars I could have had new "cups." :yes
Title: Re: Fork Maintenance
Post by: Wescoe on January 11, 2012, 01:25:41 AM: So long story short, I bought this bike with about 54,500 miles on it a few months ago and it now has a tick over 56,000. I have fairly complete maintenance records. I'm showing a Stanchion (31422312032) and gasket (31422312928) were replaced around 49,500mi. The records dont indicate which side, but I'm currently leaking oil out of the left fork leg through the dust seal. I also show a "replace fork seals" service totaling $191.25 completed at 48,200mi on 10/28/08. The "fork seals" (again no part number) were replaced at 40,700mi on 7/22/04. Fork seals roughly ever 8k miles seems a little excessive to me. Is this common on these bikes?

So, I guess I should replace 1, 3 and 5 in both legs so I have known good parts in there. I'm a bit concerned the seals seem to be going every 8k miles recently (last 15k miles or so). At least one stanchion was replaced, I just dont know which one. I'm going to contact the previous owner tomorrow, however I don't think he is all that mechanically inclined. Don't know how much useable info I'll get out of him.
Title: Re: Fork Maintenance
Post by: wmax351 on January 11, 2012, 01:29:10 AM: Something else might be up. Check if the stanchions are straight, and if they are pitted at all.
Title: Re: Fork Maintenance
Post by: Wescoe on January 11, 2012, 01:35:43 AM: Yea, my gut says the right one had a similar problem and was addressed with a new stanchion and now the left leg is experiencing what the right one is. Guess I won't know till I pull it apart, but I like to have all the parts I need to do a job before I start. I'll inspect everything carefully and do my best to figure out if something else is up.
Title: Re: Fork Maintenance
Post by: Rick G on January 11, 2012, 02:09:37 AM: Most of the K100 forks have a bush on the stanchion so the tube and leg don't contact and wear but the bushes do wear and let some slack in and this makes the seals leak. Check for wear and you may have to replace the bushes.
Title: Re: Fork Maintenance
Post by: Wescoe on January 11, 2012, 02:17:27 AM: Is this the same on the K1100 (post '93 models)?
Title: Re: Fork Maintenance
Post by: Rick G on January 11, 2012, 04:50:26 AM: Quote from: Wescoe on January 11, 2012, 02:17:27 AM
Is this the same on the K1100 (post '93 models)?
Yes all the K1100s had showa forks and all were like I described. The ones that didn't have those bushes were I believe the Marrzochi forks on the K100s only.
Title: Re: Fork Maintenance
Post by: Inge K. on January 11, 2012, 05:15:14 AM: Late K100RS 4V and 1100`s share the same fork.

What Rick G. have in mind is the earlier mentioned part #5.
It also is another bush at the bottom of the stanchion.

If part #4 (stepped washer) is mounted wrong way in, it contacts the seal lips
which would start a leak.

Before ordering parts also check part #2 (circlip), if water been present over time
these ones could be so heavily rusted that they breaks when dismantling.

Inge K.
Title: Re: Fork Maintenance
Post by: Inge K. on January 11, 2012, 05:24:24 AM: All 1100`s, K1 and K100RS 4V have Marzocchi forks which also have bushings,
Showa is used on late K75`s.........Showa = 41,0mm.........Marzocchi = 41,7mm.

Earlier used Fichtel & Sachs don`t have bushings.

Inge K.
Title: Re: Fork Maintenance
Post by: johnny on March 23, 2012, 03:37:27 PM: once i replaced the upper and lower bushings on the bug... the seals never leaked again...

just saying...

j o
Title: Re: Fork Maintenance
Post by: eyeofcy on May 06, 2013, 01:25:06 PM: Hey all, is there any documentation (pictures or video) describing fork seal and spring replacement for a K100RS? I have progressive springs coming from Progressive Suspension and would like to renew the wear items while I have it apart. That is, if I can figure out how it all comes apart. I've done a lot of wrenching on the rest of the bike but have never taken a set of forks apart before. Might as well have a look at the head bearings as well as the bike has an incredible amount of head shake if I take my hands off the bars.

Thanks in advance for pointing me in the right direction!