Proper damper rod setup in 1989 K75C Front forks

[fuego]

Hi,

I just dismanteled the front fork of the 1989 K75C, which is undergoing a frame-off restauration alongside my 1987 K75S which is also on a frame-off restauration.

I already discovered the difference in both setups. The C is damped on both sides and the S is damped on one side only. Springs and spacers are different too.

My question :

The Clymer calls for one only rubber o-ring on the damper rod per side. I've discovered two o-rings, one of them mangled in the little spring. Both K's had leaking fork seals and were missing fluid. The C was really not damped anymore (hairy ride !), the S was manageable.

Now is there one or two rubber o-ring on the damper rod and where are they going ?

Anybody have a picture of that ?

The best I found was on e-bay, where a guy sold a complete fork in pieces, and I think I saw 2 o-rings !

Man. I'm going insane over this issue, no picture of this anywhere !

Thanks for help,

Ignace

 

[88bmwjeff]

I ran into this when rebuilding the forks on my 88 R100 RT. The was a second O ring not indicated on the parts fiche. I've been told that the forks on the monoshock R100's of my vintage are somewhat similar to the K bikes. Looking at the parts fiche, they do seem to have a lot of similarities. If they are similar, here's how mine went together. For K75S parts fiche, one O ring is between the flat washer type piece and the small spring--this is indicated to be part 8 on BMW's parts diagram. The second one is not indicated and would go on part 5 of BMW's parts diagram. I hope this helps.

 

[fuego]

Thank Thanks Thanks !

Jeff,

This is an absolutely I N V A L U A B L E information not available elsewhere on the net.

Yes the K75 and the K100 of the pre- 08/1991 era where build the same as I could figure out by my lectures. The one thing that was different is that the K100 was damped on both fork and the K75 on only one.

Just wondering how many K75 and K100 forks are rebuild the wrong way using original part fiche or Clymer illustration !!!

Thanks ! Thanks ! Thanks !

Man I have to say you make my day, and probably the day (and wooos... for the forks with the missing o-ring) of a lot of people around here !

Ignace

1989 K75C
1987 K75S

 

[drneo66]

Welcome to the weird world of K-bike forks! Years, models, different manufactures, and upgrades all make for a fun time!

Looks like the parts fiche only shows one, but if you notice under the "quantity" needed for the job, it lists 4 total (2 per fork leg)

https://shop.maxbmw.com/fiche/DiagramsMain.aspx?vid=51741&rnd=09082020

 

[fuego]

Welcome to the weird world of K-bike forks! Years, models, different manufactures, and upgrades all make for a fun time!

Looks like the parts fiche only shows one, but if you notice under the "quantity" needed for the job, it lists 4 total (2 per fork leg)

https://shop.maxbmw.com/fiche/DiagramsMain.aspx?vid=51741&rnd=09082020

Indeed ! Didn't notice the required field ! But then again we need a place to put them on. Upon dismantling my forks, there was 2 o-rings, one as per the diagram, the other mangled in the little spring, which was obviously not the right place to be.

As for discovering the BMW Motorcylcle world, it's been a real pleasure with the search tool on this forum !!! But yes they have idiosyncraties !

Just got the two bikes on last september. Been riding the S more than the C. What a perfect bike for me (the S). Always used to have bikes. The last one was a Sport Touring one (Yamaha FZ1). 25 kg lighter than the S, nearly twice the power... Impossible to stay under the limit with that one... (few speeding tickets...) . With the S, no such problem, it cruises soooooooo smoothly at 70-75 mph ! A great bike undergoing a frame-off restauration .

Thanks for the info, this forum is so full of nice knowledgeable peoples ! Hope, when the restauration is complete and that I will know the bike from top to bottom that I will be able to help a little bit around here.

Have a nice day,

Ignace

1989 K75C
1987 K75S

 

[88bmwjeff]

Welcome to the weird world of K-bike forks! Years, models, different manufactures, and upgrades all make for a fun time!

Looks like the parts fiche only shows one, but if you notice under the "quantity" needed for the job, it lists 4 total (2 per fork leg)

https://shop.maxbmw.com/fiche/DiagramsMain.aspx?vid=51741&rnd=09082020

At least on the K bike parts fiche, they indicate the proper number; however, the parts fiche for my bike indicates only two. It was a bit of a surprise to realize I needed an additional two to complete my rebuild. That was 10+ years ago though. I will be going through them again with me refresh that I will be starting soon.

 

[88bmwjeff]

Jeff,

This is an absolutely I N V A L U A B L E information not available elsewhere on the net.

Yes the K75 and the K100 of the pre- 08/1991 era where build the same as I could figure out by my lectures. The one thing that was different is that the K100 was damped on both fork and the K75 on only one.

Just wondering how many K75 and K100 forks are rebuild the wrong way using original part fiche or Clymer illustration !!!

Thanks ! Thanks ! Thanks !

Man I have to say you make my day, and probably the day (and wooos... for the forks with the missing o-ring) of a lot of people around here !

Ignace

1989 K75C
1987 K75S

Glad to help