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Normal Topic K100 Front end rebuild (Read 377 times)
Tony Smith
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K100 Front end rebuild
02/22/18 at 01:23:30
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Here goes nothing, third attempt at posting this, I think that problem was my overly large photos.

Anyway, as some here will recall I bought what was sold to me as a K100RS front end to upgrade the front suspension of my R65. I boought "sight unseen" via Gumtree, a antipodean poor-man equivalent of Craig's List.

When the bits arrived I cast my eye over them briefly, simply to confirm that everything seemed to be there and put them into stock, not that looking more closely would have done anything, but the last few days have revealed a few things I should have spotted and addressed a long time ago.

Stripping the fork legs out of the triple clamps revealed that the butcher who owned this front end previously was a dab hand with a hammer - anything that didn't fit perfectly first time got a good does of percussive assistance.

See the photos of the tops of the fork legs, not only was he a dab hand with a hammer, he had serious anger issues I suspect. The second photos shows my initial rough removal of high points on the OD so that I could get the legs out of the triple clamps - a few minutes work with a bastard cut mill file.

Once the fork legs were out removing the lower race was a bit of a battle. In the past all I've needed to do on most BMW steering spindles is make one or two passes over the inner race and the heat usually causes them to expand enough to fall off. Not this one, it hung on grimly till I had ground all the way through for a significant portion of its length and then deployed the cold chisel to deal with the bits that were too close to alloy. It was a grim struggle, but I won in the end.

Inspection of the triple clamps reveals that Mr Butcher (or his cousin) probably fitted the last set of bearings, the grind markings on, and divots out of the spindle are surprising, but fortunately I don't think they have in any way compromised strength. I looked long and hard at the underside of the bottom clamp looking for evidence that the spindle had ever been pressed out (in which event the triple clamps were for the bin, but found none (thankfully).

With the forks out of the triple clamps it was time to start tearing them down, and therefore sadly time to face up to the horrid damage done to the ends. I used my bearing puller to press the caps into the forks and then used my Dremel to clean up the tops of the fork legs.

Because of access problems I used a fine burr and did what I thought was the minimum amount to get the caps out. One came out cleanly but the in the case of the other Mr Butcher had flogged the cap so hard the channel that partially retains the retention clip was collapsed on the clip - the only way I could get the cap free was to clamp the clip in a vice grip and then apply main force to pull the clip fractionally through the slot in the cap which only took about 20 repetitions of the process to get the by now VERY mauled clip out of the cap and fork - at which point the caps came out with minimal persuasion.

Once the caps were out I was able to remove the spacers and springs and then leave the fork legs inverted in an old saucepan for a couple of hours to get most of the oil out - see the photo for the truly horrid mess that came out.

My rattle gun dealt easily with the bottom retaining bolts and in a jiffy the legs were out of the sliders. Given how everything else had gone I was pleasantly surprised when the sager clips and valve bodies were easily removed, allowing the damper rods and the utterly worn our damper piston rings to simply fall out.

See the general arrangement photo - just like an R65 fork - only better (I hope).

I mentioned that these forks were sold to me as being from a K100RS. This simply is not possible as the sliders are clearly marked "BREMBO" and bear a 1984 casting mark which is a bit before the RS model was released. More to the point, only the very earliest K100s had brembo forks, BMW moving production to Fictel & Sachs and then ultimately (with the 16 valve model) to Showa.

As an aside, after my recent go-around with the KLE forks, I want to deal with another set of Showa forks like I want an additional hole in my head!








  

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1978 R100RS| 1984 R65 | 1984 XT350 | 1992 KLE500 | 2002 R1150GSA
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Tony Smith
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Graduate, Wallace and
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Posts: 1786
Location: Cairns, Australia
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Re: K100 Front end rebuild
Reply #1 - 02/22/18 at 01:33:21
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Continued.....

First photo is of the "Brembo" casting mark on the fork legs - perhaps I should try and sell them to a collector of K-bike antiquities, they are quite rare, or so I'm told.

With the forks stripped, the last thing to do was to try and neaten up the tops of the fork legs - I'm quite proud of the results. The caps now fit easily and the O ring will seal on the undamaged section of the legs.

So there it is - a lesson in carefully inspecting goods purchased unseen, preferably before a couple of years has passed along with any possibility of taking the seller to task.

I'm confident that once re-assembled these forks will work perfectly and the damaged tops can be hidden under the new plastic covers I bought for them and hopefully be further disguised by the R65 instrument binnacle.

One last thing, this is a piece of real BMW cleverness - run the brake lines down the steering spindle shaft and avoid all the finicky problems of trying to place them so they don't get kinked or are not int he way - they should have done this a long time ago.

My Dremel is a recent purchase as my wife complains bitterly that my air powered die-grinder has a nasty harmonic that drives her insane - it is of course a Chinese copy and frankly it covered its $30 purchase price in cleaning up the fork leg tops.
  

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1978 R100RS| 1984 R65 | 1984 XT350 | 1992 KLE500 | 2002 R1150GSA
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Ed Miller
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Re: K100 Front end rebuild
Reply #2 - 03/06/18 at 11:18:58
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How are these any better than original R65 forks?
  

Ed Miller
'81 r65
Falls City, OR
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Tony Smith
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Re: K100 Front end rebuild
Reply #3 - 03/06/18 at 14:08:05
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Ed Miller wrote on 03/06/18 at 11:18:58:
How are these any better than original R65 forks?


Significantly stiffer (not that the originals are all that bad) is the first consideration, followed by the availability of cartridge emulators not available for the R65 edition. The real advantages are when considering the front end as a whole - wider front wheel to allow more "modern" rubber and twin 4 spot brakes.

I do not expect the difference to be "Earth Shattering" but the K100 front end is a later generation in terms of thinking over the R65.


P.S I do have the fork brace that BMW thought they could omit because the K100 forks were so much bigger than earlier models. BMW were wrong, but with a brace the K100 had a far more stable front end than any BMW that went before.
  

1978 R100RS| 1984 R65 | 1984 XT350 | 1992 KLE500 | 2002 R1150GSA
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Ed Miller
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Re: K100 Front end rebuild
Reply #4 - 03/08/18 at 10:23:07
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Oh!  I was thinking R100, not K100.  Big difference.

I'm curious about those cartridge emulators too.  Luckily I almost never ride modern bikes so I don't know what I'm missing.

  

Ed Miller
'81 r65
Falls City, OR
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Tony Smith
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Re: K100 Front end rebuild
Reply #5 - 03/08/18 at 15:09:32
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Ed Miller wrote on 03/08/18 at 10:23:07:
Oh!  I was thinking R100, not K100.  Big difference.


You know the funny thing is that The  K100 forks are truly just like the R65 forks, only slightly bigger diameter, with a slightly better damper rod and a more modern, shorter spring and spacer system. Anyone who has ever pulled R65 forks apart would feel right at home.

Ed Miller wrote on 03/08/18 at 10:23:07:
I'm curious about those cartridge emulators too.  Luckily I almost never ride modern bikes so I don't know what I'm missing.


Essentially they replace the valving in the damper rod and have screw adjusters so you can play with both compression and rebound damping. Some, (but not the ones I bought) are "cockpit" adjustable on the fly.

Actually, modern bikes are forever ruined for me now. Every time i ride the GSA I am reminded how good the Telelever system is and I find myself wondering why why other manufacturers persist with traditional forks, and most of all why BMW went back to them. Even f you do not go hard (and I certainly do not anymore) riding a telelever front end changes your perception of motorcycling.
  

1978 R100RS| 1984 R65 | 1984 XT350 | 1992 KLE500 | 2002 R1150GSA
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orforester
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Re: K100 Front end rebuild
Reply #6 - 05/16/18 at 18:28:25
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Tony, I have had several K100 RS/RT models and worked on several others RT/LT models.  All of the forks are in the triple tree with some kind of glue cause they are a bear to get out.  I too have ruined a fork beating it out of the triple tree with a socket and hammer, big A## hammer.  Sorry for your troubles, seller should have warned you about the damage.
  

Bob
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Tony Smith
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Re: K100 Front end rebuild
Reply #7 - 05/16/18 at 18:40:01
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orforester wrote on 05/16/18 at 18:28:25:
T  All of the forks are in the triple tree with some kind of glue cause they are a bear to get out.  .



It's not a glue, the cause is good old simple electrolysis. Stainless steel fork leg and alloy triple trees.

There is no need to beat up on them, there is a simple set of tools you can make at home that makes it extremely easy to change any Airhead/K-bike etc forms.
  

Fork_leg_installers.pdf ( 614 KB | 9 Downloads )

1978 R100RS| 1984 R65 | 1984 XT350 | 1992 KLE500 | 2002 R1150GSA
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