Oilhead Fork Seal Replacement

By: AdvWisdom
Title: Oilhead Fork Seal Replacement
Sourced From: advwisdom.com/a/oilhead-fork-seal-replacement/
Published Date: Mon, 20 Jul 2020 00:52:37 +0000
Replacing Fork Seal (oilhead)
I’ve busted another (it’s the 2.nd in 4 months) fork seal and I intend to replace it myself. I’ve searched the wisdom here and it looks simple. Just to make sure, can the wrench gods confirm the following steps:

a) With a 15 mm and a 19 mm loose the stanchion from the top triple clamp

b) once loose, the stanchion will move down inside the slider.

b) remove the plastic black band at the top of the stanchion.

c) unscrew the cup (is it a sort of dust seal ? is it screwn in?)

d) remove a retaining clip

e) pry the busted seal off. (anyone knows standard seal dimensions?)

f) Install new seal, reverse the rest of the operation

g) take front wheel and axle out, take air purge plug at top of stanchion out and drain fork leg at bottom drain plug.

h) fill 0.47 l of SAE 5 susp. oil.

Is it something like this or am I totally wrong? Why do these shites blow if there’s no susp internals inside? Are we supposed to purge the air regularly like on real forks?



jdiaz 10-07-2003 01:09 PM

Don’t remove the slider at all. Just remove the fork brace bolts, the axle, and the brake caliper, and the fork lower drops right onto the garage floor. At least, that’s how my memory remembers it. I do know that there is nothing positively attaching the slider to the lower fork leg.

The rest of your procedure sounds fine, although I wouldn’t even bother changing oil.



cj1150gs 10-07-2003 03:54 PM

1 Attachment(s)


Sorry, it may be my english. I am calling stanchion to the inner fork tube (attached to the top triple clamp) and slider to the outer tube (attached to the bottom triple clamp / telelever arm).

So do I need to loosen the lower (outer) fork leg? I though that, by releasing the inner from the top triple clamp, this inner would move down inside the (outer) bottom fork leg, allowing me to take the seal out by the top part. Hum… maybe a drawing…


I just redid my left fork seal, and the upper (shiny part) of the left fork, today for the 2nd time since doing both in Achorage early this May, I tried to do it with out taking the entire fork out of the mounts. But it will save you time and knuck skin if you just take the bloody hold thing out. Rememer to re-aline the front axel before putting the tire back on. i tighten the bolts that #4 on preivioius pict. withthe axel in then put the tire back on.

as for replacing the fork seal. by taking the entire lower fork off you will have the ability to remove the bad seal easier. they are really tigith fit. also be very careful on putting the new one back in not ot damage the inner seal ring part of the seal. I used a large socket for to evenly get the seal to sit flat on the metal o-ring that goes below it. I had BMW Anchorage show me how to do it with their BMW speciality tool, I used a large socket that just fit into the lower fork section. If you have a friend with mechanic shop they should have a large enough socket. .

in addition, i put a bit of extra grease on the top cap to help keep dust getting into the seal and wearing it out quicker. To get old seal out is a pain and you need a L shaped hook type of tool to pull it out. that is why i take the lower section, so i can use my feet and legs to get a good hold on the fork to pull the seal out.

thing to check while doing seal replacement
take the tiem to clean out any grime in the bottom of the fork lower section, i use a little but of desiel fuel as a solvent and clean inner part of the fork of and grime fork oil that did not drain out.

the uper part of the fork (shiny part) will slide in easily if the seal is sitting flat on the lower metal o-ring. also take out the tiny hex bolt on the top of the upper part of the fork to let air in as you re-insert the lower part back onto the upper part. and then when everything is at the right place tighten the tiny screw back to seal the fork.

In addition, you should check you upper fork section to see if there are any fine scratches… i had some bad ones from all the dirt roads i ride in Colorado, that could be the reason you seals are wearing out so quickly. And buy a pair of fork covers.

Remove front wheel and brake callipers:

Loosen the inner top from the top triple clamp:

Loosen the pinch bolts on the bottom triple clamp:

Lower the fork tube in the lower triple clamp, let the cup(dust seal ) rest agaisnt it and push down to extract the dust seal.

how it looks once out:

Now remove the air purging little bolt from the top of the inner tube. Then pull the inner from inside the outer. Beware oil spillage!

Now remove circlip:

Then pry the seal out with a big flat blade screwdriver. Protect the top of the outer tube with some plastic piece or something:

Bellow the seal there’s a large washer (rusty in my case):

Where it all seats (once cleaned):

All in pieces:

Now, when I took the inner from the outer I saw that the seal didn’t have any visible damage. The inner is also in good aparent shape without scratches… humm.. I begin to suspect crash is right. Let’s put the inners in the truing stand:

Shit. Crash is Right. About both inner tubes.

I didn’t have my feeler gauges handy. But I had a book 1 cm thick and a 100 pages :): . I can slip 2 pages but not three bellow the middle of the inner. So I guess it has a runnout of 2 to 3/10 mm. Is this acceptable? I can turn the inners inside the outers with no effort…

The Telelever A-arm looks OK. (Apart from the fact that it hits the Hepcko & Becker crash bars :splat.

I can’t see the dreaded cracks in the paint.

The grease under the dust cup is common practice on dirt bikes (real ones, that is). But the manual of my KTM says to put new grease in every 15 riding hours! So, I guess it is a good thing to do if we do ride off-road, but it should be at least inspected on a regular basis (like monthly?)

I borrowed a friend’s micrometer and built a pennytech measuring stand:

As expected, the tubes are more or less inside spec (0.016″)regarding runout. (one is at 0.015″ and the other at 0.018″).

Well then why does the shop manual say to do so?

BMW Shop Manual Page 31.9]
• Install fixed tube.
• Install washer (6).
• Push the lightly oiled shaft sealing ring fully up to
the stop on the slider tube, then press home by
tapping lightly and using threaded bush,
BMW No. 31 5 611, expander,
BMW No. 31 5 612, and reducing adapter,
BMW No. 31 5 613.
• Install retaining ring and dust wiper.
• Insert bleed screw (1).
• Bleed telescopic forks under zero load.