Hi folks.
I had to remove the forks to replace the gaitors the other day.
After taking the wheel and mudguard off, I was suprised to find that the left slider could be almost fully slid off the stanction. The only thing stopping it pulling apart had been the wheel spindle and mudguard!

Nothing for it but to strip the fork down and investigate. That's when I found that the circlip at the bottom of the stanction had come out and was rattling about inside.

That was a relief, I imagined something very expensive had broken! But this was easy to fix. I just hope it doesn't happen again.

Unfortunately I lost quite a bit of the oil from this leg,so I was wondering if anyone could give me some advice on changing the fork oil, best way to do it, and what weight and quantity do you recommend.

Many thanks.
Steve.

Kcrank,
I forget where this info; came from but it may be what you want.

On the Fichtel Sachs fork you can remove the lower legs without removing the fork tubes from the triple clamps. Remove the brake calipers ( wrap them in rags and bungee them away from the fender ) remove the wheel and front fender. If you look at the bottom of the fork slider you will see a 6 mm allen screw recessed into the slider above the axle. There is an opening in the bottom of the leg to allow you to use a long allen wrench to unscrew this screw. It will probably require an impact wrench to break the torque on it. Drain the fork oil before removing this screw, but removing this screw allows the fork slider to be removed from the fork leg. The screw holds the slider to the damper rod. Once the slider is in your hands, work a big flat screwdriver blade under the seal and gently twist the blade to work the seal loose. Once the seal is out, thoroughly clean out the slider with solvent.
To install a new seal I use the BMW seal driver. Otherwise, you could place the seal in the end of the slider and lay a flat piece of wood over it then try to gently tap it into the hole with out getting it cocked sideways or damaging the seal lip. Oh yeah, really important, you must sand the damage to the fork leg that caused the original seal to fail. Some little sharp edge from a nick in the fork leg damaged the seal and caused that leak. What I do is use a strip of 400 grit silicon carbide paper to sand the front and back surfaces of the leg in a cross hatched pattern, rubbing the paper across the leg at an angle in a manner like you would use a rag to shine the toe of your dress shoes. If you don't do this you will immediately damage the new seal.
Put plenty of white lithium grease on the new seal when you slide it back up the fork tube so you don't damage the seal on installation.
Ajays

Fork Oil for "Fichtel/Sachs" Forks I assume you have this type?

K100 330+-10cc [11.62+-0.35imp fl oz.] or [11.16+-0.34US fl oz]

Oil is available light/Med/Heavy. take your pick.

Ajays

Thanks Ajays. I don't know what grade oil is in there now, so I guess I'll try a medium weight and see how it feels.

Much obliged,
K'c.

I chose 10W in my 'new' set of 'S' forks on my 1987 K100RS which I've fitted recently. After a hard week's use I think it's a tad too stiff for mine and the bike's weight. I'm going to try 5W. In my other BMWs using 5W (or even 7.5W) the suspension seems to respond better to slight irregularities in the road surface. 10W can make the suspension feel a bit jiggly which can be felt through the 'bars. Unless you're a bloody great beast yourself or ride fully laden with a cuddly, doughnut loving pillion I'd stay away from heavier weights. I used it because I'd a new unopened container of it on the spares shelf and thought the bike needed to be more firm upfront. Not so, I have found. The 'S' fork's shorter travel and stiffer feel take care of 'firm' all by themselves!

Cheers for that TWB, I don't ride particularly quick, and prefer a softer ride, so it looks like 5W oil would be a good bet for me.

Just out of interest, has anyone else had the same problem with the circlip coming loose.

The circlip fits into the bottom of the fork stanction, and holds the damper mechanism in place, which is being pushed against the circlip by the fork springs.

Without the circlip. the whole damper mechanism can slide straight out of the stanction, as it's attached to the fork slider and will move with it.

The only thing stopping me from simply pulling the slider off the stanction was the vacuum created in the fork by pulling on it.

The supprising thing is, I never noticed any quirkiness in the handling with only one fork working properly, although as it was probably like it when I bought the bike about a year ago, hopefully I might notice an improvement now.

Steve.

An old trick for finding the rock cut on the surface of the fork tube (without cutting your hands):

Use an old pair of pantyhose, and lightly draw them over the surface of the fork tube. The hose will 'catch' on the snags in the surface.

 oh yes, the pantyhose trick. It reminds me of my dating days ...  my then girlfriend and I were driving along late at night when a charge light went on... I got out looked under the bonnet and found that the fan belt was missing. I calmly opened the door and said: " would you please give me your pantyhose?". The look on her face was priceless  Yes, I did have to explain. That panyhose/fan belt got us home, a good 30 min drive. 

Hi Ned,
Bin there Dun that....did you stop on the way?
I see some of the lads from FB are here.
Ajays

The BMW fork oil I have for my K100 RS is SAE 10, broadly speaking if 10 is too thick for you try a 50/50 mix of 5 and 10 if you can't buy 7.5 locally and you would like to try it.
Regards,
K-BIKE

My bike shop sells fork oil in tins marked Light / Medium / Heavy. That is all that is required really.
Ajays

We stocked and regularly sold a range from 2.5W, 5W, 7.5W, 10W, 15W, 20W and even up to 30W fork and suspension oils in our shop. But I s'pose that gets to be like a pub with too many draught choices.
Cheers!

I'm new to BMW fork oil change but I have done others.....This is how I am going to do my R100RT which I am going thruat the present time. ( please advise if I am wrong)..1. pull plugs from top of forks
2. remove drain plugs at bottom of each fork,do not mix up bolts you take out
3.Drain as much oil as you can compress the forks several times and let sit over night.
4.put plugs back in the bottom of each fork leg
5.Get proper oil and amount required in each leg(EXACTLY) no more/ no less.
6. Get two plastic baby bottles/fill each exactly with the oil you need.
7. One for each leg don't spill a drop/ tape wire in place or hold till morning till all has drained in each fork,that way you have the VERY EXACT PECISE oil in each fork.
8.Put top plug back in..done!

I have not done any BMW work but in the past this has been what I have done.. to triumphs,yamahas,hondas Harleys etc..

You won't hurt my feeling if this is wrong on the beemers..I never want to give out bad info.
Ried Safe.


Sprocket

Good plan, that is the way to do it when you are prepared to take your time over night. If the oil that comes out is dirty or smelly when it comes out consider doing a rough fill and then going for a reasonable ride with the forks pumping up and down on speed humps etc. and then drain and refill that will help flush out dirt.
Regards,
K-BIKE

Thanks for the replies folks, It's got me pondering..... I've always read how important it is to get the oil quantity exactly the same in each leg, and tried my best to do so, but I'm wondering why it's so critical.

As I understand it, the oil passes through holes in the damper rod, hence the thicker the oil, the greater the damping effect. So as long as the oil is full enought to cover the holes, it will work.

Is it the volume of air above the oil that's the important thing? I assume the pocket of air will have some effect on the forks performance as it compresses, but is it really that critical?

Just wondering....

Too little oil and your forks will potentially wallow or feel mushy, too much oil and they will not respond well to the slight ripples in the road surface. It will feel jiggly through the 'bars. It has a lot to do with the air that's above the oil as it compresses. Liquids (fork oil) do not compress as much as 'gasses' (air) do. The engineers have calculated the ideal level, have made the recommendation, and it's been working successfully for most of us for a dog's age.

Well... air will compress and oil will not. My reading on the subject is that if you exclude air the oil passage through valves will be very slow even if you take oil with the least viscosity.
I bit like the brakes... any air will give you that spongy feel you don't want.

I get this discussion started as I don't really have much expertise in this.

Someone goofed.. In changing fork oil I measured carefully one fork had 1and1/3rd cup and the other was shorter on oil.....
They are draining overnight and refill in am as soon as SOMEKIND sole tells me how much oil go in there..I am not good at math especially LITERs.. If not I will figure it out.

I don't like air in forks..Belongs in ballons(always Leaks)

I am going to put 10 wt in forks, stock from factory has 5 weight according to what I have read.........I am new at Beemers all others not so new....

Moved front end back to factory settings,,previous owner lowered the front forks..( they sell step thrus) HA!

Ride Safe.

Bruce Bilger( Sprocket)
Fremont,Ohio

A stock standard K100RT from 1985 takes 360ml or 360cc of oil in each stanchion, which, if you're metrically challenged, is 12.17 US fluid ounces.
10W is OK but unless you're a regular buffet table attendee or doughnut eater you'll likely find it too harsh. I recently drained the 10W from my bike and refilled with 5W...sweet and supple once again.

Two Wheels Better:

I like Buffet, I eat doughnuts, and at times I am a little HARSH!

Thanks for the correct fork cc's.

I have gone heavier on fork oil in the past and I weigh 245 lbs so I will try the 10wt. If it sucks I will do over.

Thanks for info.

Sprocket
Fremont,Ohio

No, you'll be right on the 10W then. At 80 kilos (couldn't resist) I can punch above my weight but don't settle the suspension like you big blokes do.

I once broke down in Fremont, Ohio. It was back in 1984/5 and I was travelling across your vast country in a huge car from the early '70s. I reckon it was an Electra 225 if I remember it rightly. It was surreal. Got going after a day. The people were friendly. Good memories.

Cheers!

The air above alters the spring rate I believe more oil increases the spring rate less oil reduces it. I put the recommended amount in myself. Although that said I may experiment one day.
Regards,
K-BIKE

NOBODY should break down in Fremont,Ohio....but I am glad they treated you well..............

Sprocket.

I have always been told oil being exact, but why exactly,I don't know?
I drained mine the other night each leg was different.. The ride was
garbage.....today after the exact new 10 wt I couldn't believe it.... I don't think it was 25 years old,Who knows?????????????? But I know its right on the money,and thats as good feeling.!

Ride Safe!

Bilger
(sprocket)

Here is a table with the oil quantities/capacities. Note that for the K11, if you only replace the oil, the quantity is different on each leg.



Bert

Having put 15 wt in my forks I realise this is too heavy so I am changing to a lighter weight. My question is, I have noticed that the rear shock is bottoming on bad road surfaces, will softening the front alleviate this? As a suspension novice a simple explaination of how front and rear interact to changes and what settings should be like would be useful. My bike is an 89 LT and I have recently fitted a Hagon rear shock with 3 position spring adjuster.

Martin

martin sometimes this can be a preload issue ......there are a few posts about this ...spattered across the forum i suggest you read up on it .

try the search feature.

although many older shocks have lost their seal and possibly the contents of the shock chamber damping oil. if you are lucky some of them can be refurbished with seals oil etc

but you need to go through the setup process first to gain a knowledge of your equipment and situation, along with a friend that can take the measurements when required .

but basically you need to setup the preload (spring tension ) so that when loaded ..(you sitting on the bike ) you acheive a sag of about 1/4 to 1/3 of the full travel of the rear shock ....this is just a rough indication there are other factors involved .

have you tried looking for the setup information on the manufacturers website ?

can hagon units be rebuilt , is it new ??

hope this helps

My 85 K100rt needs new fork seals. Lower fork legs say Brembo. What kind of forks do I have?

You got Fichtel & Sachs, aka Brembo, aka Bmw.
Fork seal, part # 31 42 1 451 478.

Thanks Inge. Hoping the dealership has them in stock.

Don't buy the pyramid parts seals off ebay they are garbage of the highest order.

My fork seal on the left is also leaking and I am planning to changed both seals and place a rubber boot after. Any recommendations on good website/place to buy shock seals? Fleabay is scary sometimes.

This guy is in UK but one of the other furumites posted his site http://www.gaiterman.co.uk/