Hello Brick Pilots,

I have a K100RS 2V (1986), see my Avatar space for details. I am about to service the forks, callipers and change the front tyre. The forks probably require 330ml of oil and here is my question:
how can i tell which forks I have?

Can anyonetell me how to positively identify them please.

I'd say you've got the 360ml fill forks on your model, same as mine, until I swapped them for the sport forks from a K75S with the tiny 'S' inscribed in the aluminium top cap. Unless a previous owner did something you don't know about that's your fill amount. If you do put only 330cc of oil in, and your forks require the 360cc level, you'll notice the damping feels spongy and vague. Too much oil and she'll jar your fillings over tiny road irregularities.

If your fork legs have a "rib" running down them (on the front edge), they are Fichtel and Sachs. 360 +/- 10cc.

The Showa have no "rib" and are for K75's 1983 onwards. 410cc at oil change or 420cc when dry (from a rebuild for example).

According to the Haynes manual.

Thank you! It looks like 360cc is it.

I have a 1992 16 valve K100rs and my original BMW handbook states 400cc of oil in each leg at oil change!

Hi there, as far as I know if your forks have and S stamped in the top nut (the one you have to retain to release the filling plugs) then your suspension is sport type and requires 280 cc.
Best regards
JAP

My -88RS with an F&S fork has been happy with 370 ml in each leg.
No S stamped.
Don`t overtight the drain plugs when changing oil.
I had to fit helicoil inserts due to hamfisted spannering.
Cheers,Wikur!

Can anyone advice me please?

My left fork is leaking oil, means I need to replace the seal / gasket. On the lower fork bridge it says "Paolo Tardossi" (?).

How much oil shall I put in each fork?

Thanks.

I think you`ve got this.


Its an aftermarket forkbrace for K`s earlier than -88.
Made by "Paolo Tarozzi,Italy".
0,37L in each leg should be fine,works for me.
Cheers,Wikur!

Hello Wikur,

Thank you for the information.

I am travelling out of town now. I will upload the picture of the fork on my bike.

Cheers.

I hate to crack this thread open again, but I guess this place is as good as any to ask.

1985 K100RS. Has 'Brembo' forks with rib on the front, no 'S' on the cap. How much oil per leg? I'd like to do this in the next couple of days.

If your fork legs have a "rib" running down them (on the front edge), they are Fichtel and Sachs. 360 +/- 10cc.

Ok. The leg has "BREMBO" stamped near the top which was throwing me off.

I saved the following which was written by the very knowledgeable Brian Curry so this is all his work.


Front Fluid Quantity and Suspension Response



November 1998
Brian Curry

My latest K75RT, a 92, had Showa
forks. This is the first I had Showa's. The front of the bike was scary under
braking. It dove like crazy. I thought I needed new Progressive Springs.


As part of the prep for running
it to the West, I drained and refilled the forks. For some reason, I checked
the amount of fluid that came out of the first fork, ~360 cc's. Odd number it
seemed. The Non-Showa RT's took 280 cc, and the non-sport suspension was
supposed to take 330 cc and the drained amount was more than this.


I checked the owners manual. It
said 280 and 330 cc's. Hmmm. I checked the manual version date. It was old...
and pre Showa... Time to call the dealer.


Lee Kundrat, of Otto's BMW
Cycles, told me Showa forks were supposed to take 410 cc's.


OK, I tried that and put 410 cc's
of BMW 7.5W oil in each leg.


Then I rode the bike. Even I, the
suspension idiot, could tell the difference. It was a night and day
difference. The dive was much reduced!! The front end suspension felt much more
composed.


Then I thought about it a bit.
The new, proper, larger fluid volume reduces the air volume above it, compared
to the way I got the bike. This means that when the fork compresses, the air
PRESSURE increases much faster than when the volume is larger. Increasing air
pressure acts like a rising rate spring. Effectively, putting more fluid in the
fork increased the spring rate a lot when the fork tried to dive. (Some time
back, HD had a brake dive reduction scheme, by isolating an air chamber that
connected to above the fork oil. It gave a "higher" spring rate, when
you were on the brakes and the fork air volume was cut off from the chamber.)


Having the proper amount of fluid
in the forks IMO, eliminated the need for a spring transplant and made the CC
jaunt much more pleasurable.


So, if you want more
"cushiness" and "plushness" although with more dive, put in
less fluid. If you want more "control" and "firmness" and
"less dive" put in more fluid. Remember there is a limit on how low
or high you can go. If you go too low, you can hear the transition from air to
fluid as the fork valving compresses. Shock "absorption" will vary a
lot depending if there is air or oil going through the restriction orifices. If
you go too high, the fork tube pressure will go REAL HIGH. The suspension may
appear to be "solid" or "locked". You might be able to blow
the fork seals or O-rings out. Either are not be good things. Remember, when
you deviate from the BMW factory values, you are on your own. Travel with care.

BWM specified fork oil
quantities/capacities have varied over the years. Here is a table of values:

Fork Oil
Quantities/Capacities


Model Leg Change Disassembl


K75 Showa L
410 cc 420 cc


K75 Showa R
410 cc 420 cc





K75 BMW L 330 cc


K75 BMW R 330 cc





K75 Sport L
280 cc


K75 Sport R
280 cc


(Has an "S"
stamped on the aluminium plug on top of the leg.)





*16V*


K1100LT L 350 cc 400 cc


K1100LT R 400 cc 400 cc





K1100RS L 350 cc 400 cc


K1100RS R 400 cc 400 cc





K1, K100RS L
380 cc 400 cc


K1, K100RS R
380 cc 400 cc

There is
a Service Instruction 31 026 92 (2547) which is supposed to have additional
information.


A ">" indicates that
the data is correct for models up to that model year from either start of
production, or an earlier date when the value was different.


This data is was correct as of
Oct 4, 1993. After that, you are on your own. But it may be some help. Why does
the amount vary from the Left to Right leg? Don't know. BMW says it does.

Yep, 360 came out, 360 went back in. Thanks fellas.

I have my K100RT original Riders Handbook and it recomends 330ml per fork. I found SAE 5 or 10 Fork Oil too soft and have been using SAE15 with good results for many years.

According to my oldest Haynes manual (`88) 330 ml was used on the model without a fairing.
All models with a fairing should have 360 ml.
My oldest genuine manual (04/88) also confirm these volumes.

And to make the confusion complete.....my riders handbook (3rd quarter `85) recommends
360 ml on all models



...........but it also was a revision on the forks during `85.


Inge K.