I'm reconstructing a crashed K100 RT (1986 I think) I have an extra set of forks. LH side & RH side forks appear to have dissimilar lengths


I should qualify "dissimilar length": One LH fork is disassembled - so I'm comparing the assembled LH one with the two assembled RH forks. With the forks removed from the bike, if I push the stanchions down until I can feel it pressing against the spring, let's call it take up the "free play", the LH one is shorter. If I pull the stanchions up as far as they can go the forks are the same length. The "free play" in the RH one is less than in the LH one.

I'm not yet able to establish how the disassembled LH one would compare lengthwise at this stage. However, if after assembly it turns out to be the same length as as the RH side forks I still have the dilemma of one "shorter" fork; which do I use in my build 1 long and 1 short or 2 long ones? What's going on; dissimilar forks seems strange?

I read in Haynes that there are differences between LH & RH forks on the K75S, but as far as I know my forks are all from K100.

I'm unable to identify if they are Fichtel & Sachs or Showa; I'm guessing F & S. The lower legs do not have lugs for a fork brace. There isn't an "s" stamped on any of them. I disassembled one RH fork and it has a single main spring and a single spacer.

Some have a spacer on top of the spring, could be that is missing or the spring is shagged but there should be no free play.
K100 forks are 41.3mm and K75 are 41mm and K1100 are 41.7mm.
AFAIK the K1100 forks are the only ones that are different left to right as they have compression damping in one leg and rebound in the other and no lugs is K100.

RicK G wrote: AFAIK the K1100 forks are the only ones that are different left to right.

TS is correct about the K75S fork, it have damping only in the left leg.
This so called sport fork (marked with "S" at the spring retainer) was later
used on the rest of the K75's untill they changed to Showa ~91.
All the K100RS special edition models did also have this fork.

Do agree that it shoudn't be any play in the up/down movement,
seems like a PO have done some mods to the spacer(s).

Inge K. wrote:

RicK G wrote: AFAIK the K1100 forks are the only ones that are different left to right.

TS is correct about the K75S fork, it have damping only in the left leg.
This so called sport fork (marked with "S" at the spring retainer) was later
used on the rest of the K75's untill they changed to Showa ~91.
All the K100RS special edition models did also have this fork.

Do agree that it shoudn't be any play in the up/down movement,
seems like a PO have done some mods to the spacer(s).

Thank you charlie99, Inge K & RicK G

I measured the stanchions, all 41.3

The "short" one behaves exactly like one would expect if that spacer has been removed. I will be opening it and will be able to confirm

Thanks again

It took me a while to disassemble. A woodworking clamp, about 1.5 meters, was useful. I MacGyver-ed a puller and also a slide hammer. I took care not to damage the inside surface of the stanchion. Fortunately I have a spare spring, spacer etc.

Anyway, it is now obvious, the fork was salvaged from either

• A burnt out bike
  
• Or a bike that was left in the sun on a very hot day
  

take your pick