Have you replaced the forks springs in your K?

[diversity48]

I recently ordered some fork springs from BMW2valve.com for my 85 K100RS. They are Wirth progressive springs and even came with instructions in German! The folks at BMW 2 valve were quite accommodating and did supply me with instructions translated to English. If you have replaced fork springs in your K bike, were the replacement springs longer than the originals? According to the instructions that came with my springs the new ones are "probably" longer than the originals. My dilemma is that although the replacement springs are progressively wound, they are about 2 1/2" shorter than the originals. My solution would probably be to cut a new spacer 2 1/2" - 3" longer from plastic pipe and use that. Not having a whole lot of experience with suspension modifications, does anyone here have experience with such a situation? I have a call in to BMW 2 Valve but have not heard back from them as of yet. Any suggestions? 

[TimTyler]

BMW2valve has Wirth part# 3142904 listed for "K75 and K100-series BMW models, up to 1991 with Sachs fork"

However bmwbayer.de has Wirth part# 3141030 for "K75S/RT bis 91, K100 bis 1990"

It's hard to find Wirth info online!

[diversity48]

Ya, I agree. It's hard to find anything available in the way of progressive fork springs for an 85 k100rs. I've been looking for a while without much success. apparently the pre 91's all came stock with the sachs forks, from all that I can find. The Wirth springs will fit, but I would think an upgraded spring would at least be the same length (but more than likely longer) than the stock ones. If I cut a spacer 2.5" longer than the one that's in there, it would work, just not sure if it will accomplish what I want from the suspension (less dive at braking).

[TimTyler]

Might be of some help:

http://www.wirth-federn.de/products/en/Gabelfedern/BMW/BMW-K-75-S-91-SACHS.html

Product No.: Spring3040 (FNR13199)

Can you tell if that matches the part you received?

[Inge K.]

BMW2valve has Wirth part# 3142904 listed for "K75 and K100-series BMW models, up to 1991 with Sachs fork"

The above listing is the problem.....K75's and K100's have a different fork from Fichtel & Sachs.
K75's have the sport version with different internals and springs, the only K100 that have this fork is the
limited production models of K100RS.

[subforry]

Both of the 2 sets of fork springs I have installed (one in the K1100) required PVC pipe spacers.  This is not uncommon.  You can use you old springs as guides for the length of the spacers.  If you want pre-load then cut them longer.  I cut mine long.  After a few rides and measuring the pre-load I cut them down to adjust the pre-load.

[TimTyler]

Jack, How long are the springs you received?

The K75 "S" spring spec is between 395-401mm AFAIK.

[diversity48]

Not sure about the length of the springs I removed. But they are 2.5" longer than the new worth springs. I dont mind making new spacers but considering the length of the old spacers, the new spacer would be almost 6" to equal what i'm talking out. Would that defeat the purpose of spring replacement?

[TimTyler]

So the new or old springs are not available to be measured?

K75's and K100's have a different fork from Fichtel & Sachs.
K75's have the sport version with different internals and springs, the only K100 that have this fork is the
limited production models of K100RS.

Your K-knowledge is limitless, Inge! I wonder if the 85 K100RS in question is part of that limited run? (or did you mean all 100RS's?)

Also, who know what previous owners have installed in your forks.

Service Guide says 395-401mm.
Progressive Suspension #1126 says 457mm

[diversity48]

Both sets of springs are avail to be measured. I'm just not home to measure them. Will be home in about 5 or 6 hrs and get some measurements then.

[Inge K.]

I wonder if the 85 K100RS in question is part of that limited run? (or did you mean all 100RS's?)

First limited production model was in -86, painted white pearl, black engine and wheels +++, 1000 was made.

Service Guide says 395-401mm.
Progressive Suspension #1126 says 457mm

I think the 400 mm is the standard springs....the sport version is shorter due to one more spacer.
To begin with only the K75S did have the sport fork, other 75's later...exept K75C.

[TimTyler]

I just pulled my Progressive #1126 springs (installed  50k miles ago) and they are still 457mm / 18".

[Inge K.]

I just pulled my Progressive #1126 springs (installed  50k miles ago) and they are still 457mm / 18".

That makes sense, as the spacers looks much shorter.

[diversity48]

ok, the measurements I just took are:

Stock Springs (or at least the springs that were in the fork) are 18" long.

Wirth Springs are 15 3/4" long.

Spacers that were sitting on top of the springs when I removed the top plug are 2 3/8" long.

I have a partial record of some (not all) of the servicing that was done on this bike before I got it and there was nothing about changing fork springs, at least no record of it in the notes I received.

Tim, in the wirth website you mentioned above, I didn't see any springs listed for an 85 k100rs.

[TimTyler]

http://www.wirth-federn.de/products/en/Gabelfedern/BMW/BMW-K-100-RS-90-4-Ventiler-o-ABS.html

and

http://www.wirth-federn.de/products/en/Gabelfedern/BMW/BMW-K-100-RS-90.html

Is there a product # on the packaging you received?

[Inge K.]

Just would mention that a -90 K100RS have a Marzocchi fork, which is different than the earlier used Fichtel & Sachs

[diversity48]

two sets of #'s on the package:

3142904

JM No. 743.00.28

I think the "4 ventiler" means 4 valve??

Both of those captions are for a '90 k100

[Inge K.]

It seems to me that the springs that allready was in your fork is from Progressive, same as Tims.
(the OEM springs is linear and usually two piece).
The Wirth springs have the same length as the standard springs.

[diversity48]

The spring that was in it is not progressively wound... (not tighter at one end).

[Inge K.]

Of some other brand than Progressive, but the same length then............ :dunno.
How about the spacers, the OEM ones is around 1,5 times the length...compared to the ones in Tim's pic.

[TimTyler]

Stock Springs (or at least the springs that were in the fork) are 18" long.
Wirth Springs are 15 3/4" long.
Spacers that were sitting on top of the springs when I removed the top plug are 2 3/8" long.

It sounds to me like a previous owner upgraded the springs (to a non-OEM spring) but re-installed the OEM spacers (trimmed?) with the new, longer springs.  Although my spacers are about 2" too (I cut the OEM spacers). Hmmm.

With both wheels on the ground, put a small level on your valve cover and see if it's mostly level (front to back). Mine is.

If you use the original spacers with the new Wirth springs, maybe it'll be level?

[diversity48]

Thinking I may just try 15 weight oil and send the new springs back.

[kris]

"ventiler" = valve....please let me know how you make out with the 15 weight oil. I've got to put new oil in mine and was thinking maybe that's the way to go. I believe my springs are stock. If the bloody winter ever ends I'll be able to get Heinz on the road!! (once I put her back together :clap:

[diversity48]

ya, kris. I'm looking forward to getting this thing back together with the different oil in the forks and will let you know how it responds. it appears that upgraded fork springs are no longer available for the bike, so I'm thinking this is the next best thing.

[TimTyler]

I'm thinking about adjusting my spring pre-load....

With the K75 on the center stand, rear wheel slightly off the ground, would anybody mind measuring the length of their Sport forks from the center of the front axle to the metal top of the fork above the top triple-tree?

Hoping to learn the average / norm. Mine currently is 31-3/4 inches.

Just found an April 2014 post of mine here where it measured 32-1/8 before I cut 3/4" off the PVC spacers, so the springs have not sagged in two years (26k miles).