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Very Hot Topic (More than 25 Replies) K100 Front end rebuild (Read 1406 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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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.
  

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1978 R100RS| 1984 R65 | 1984 XT350 | 1992 KLE500 | 2002 R1150GSA
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Semper Gumby
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Re: K100 Front end rebuild
Reply #8 - 06/06/18 at 13:41:28
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Best upgrade I ever did to my R65 Tony.

Watching your work with interest.  I believe they are 38mm forks.  I have a K75 top triple clamp that hard mounts my 12 inch pullback BMW bars.  The the K100 rubber mounts means the bars move around a bit...  Shocked
  

Bill Gould 1980/03 R65 When at first you don't succeed....Moo!
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Tony Smith
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Re: K100 Front end rebuild
Reply #9 - 06/06/18 at 15:47:22
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Semper Gumby wrote on 06/06/18 at 13:41:28:
Watching your work with interest.


Well there hasn't been too much to watch lately, paid work has interfered with my motorcycle mechanic play time. Still things have advanced slowly.

The biggest holdup has been designing the brackets so that I can still use the R65 "plate" that mounts the headlight, instruments, ignition switch and blinkers. I was a little blindsided by this as a lot of what I had read indicated that this was a "bolt up". Perhaps as a result of the fact I have very early model K100 bits this isn't so, the task has been to design brackets that do not alter too much the position of the "plate" relative to the steering head as I do not want to have to get into lengthening all the wiring.

The good news is that I think I've found a way forward and have designed brackets to act as an "intermediary" between the K100 triple clamps and the R65 "plate". The only additional holes I will need to drill in the "plate" will be to effect new lower mounts as the K100 lower clamp does not have any upward facing bolts I can re-purpose and I am simply not comfortable in drilling any holes in them.

I was concerned about the rubber mounts for the handlebars, especially as the rubbers in my triple clamp were not in the first flush of youth and didn't inspire confidence. I was initially going to turn some alloy "slugs" and simply hard mount the bars, but then I discovered that some very cheap urethane bushes that I bought when fixing the suspension of my trailer actually fitted perfectly. As a bonus they are significantly stiffer than the original rubbers .

I have promised to take my R65 on an overnight run to meet up with the motorcycle restorers club from the next city South of here - Townsville. This is a yearly event and the clubs meet half way at a small seaside village called Cardwell. It's a 200km trip for me and the meetup is on  23 June.

Last year I wimped out and took the GSA resulting in a weekend of derision, so if I cannot get the R65 mobile in time I guess I'll have to take the KLE and the thought of sitting on that seat for 200km is a strong motivator.

Over parts of my R65 project advance also. The R75 final drive I bought from Wilcom has been fully refurbished and is ready to be bolted on. Given that most of the miles the R65 does are highway miles I am interested to see how it goes in its R860 guise pulling the higher ratio rear end. If, as I suspect it will, it has no problem at all with the R75 final drive, I will try an R100 final drive I happen to have and see how that goes. Looking at the torque figures claimed by Siebenrock I think that it will have no problems pulling the R100 "moonshot" final drive which would suit me fine as it is in the later housing and is therefore "period correct" for my 1984 R65.

The other little project I am enmeshed in at present is tha I've bought a broken speedo in order to obtain the "can" and I've also bought an 85mm GPS speedo from Aliexpress - when those bits arrive I will pay a local instrument fitter to remove the broken mechanical speedo and fit the GPS device in its place. My hope s that to a casual glance it will look fairly stock.

  

1978 R100RS| 1984 R65 | 1984 XT350 | 1992 KLE500 | 2002 R1150GSA
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Semper Gumby
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Re: K100 Front end rebuild
Reply #10 - 06/06/18 at 16:23:47
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Tony!

If you could tell me the part number for the urethane trailer Bush it would save me some time for the handlebar mount. I would be in your debt.

I zip tied the lowers. If you makes two plates I will pay you for your time. Cool

Woo hoo. You did the r860 cylinder piston install. I must read about this. I saw them the other night. Bit worried about blowing out the bottom end making too much power....
  

Bill Gould 1980/03 R65 When at first you don't succeed....Moo!
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Tony Smith
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Re: K100 Front end rebuild
Reply #11 - 06/06/18 at 23:38:07
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Semper Gumby wrote on 06/06/18 at 16:23:47:
If you could tell me the part number for the urethane trailer Bush it would save me some time for the handlebar mount.



I wish I could. We have a chain of auto parts stores here called "Super Cheap Autos", its kind of like a dime store for auto parts and many of the parts are of "dime store" quality. The bushes in question were simply in a shelving bin marked "trailer bushes" (probably to avoid product liability if someone fitted them to a car) I measured them up based on what my trailer takes and it was only later that I realized that they also fit the  K100 top triple clamp.

Semper Gumby wrote on 06/06/18 at 16:23:47:
I zip tied the lowers. If you makes two plates I will pay you for your time. Cool


Done deal!


Semper Gumby wrote on 06/06/18 at 16:23:47:
Woo hoo. You did the r860 cylinder piston install. I must read about this. I saw them the other night. Bit worried about blowing out the bottom end making too much power....


Well no...not yet. I've pulled the kit out several times intending to fit it, but each time something has intervened and  it all got packed away again.

I made some intemperate comments to someone in the Facebook R65 group the other day as they were holding forth that the R65 engine just isn't suitable for a capacity increase as it is not "strong enough".

I asked him which bits were too weak to take a capacity increase and he went silent on me. Then someone else posted about all the horror stories they have heard regarding punched out R65s.

With a big sigh I gritted my teeth and let him have it with both barrels...... Below is an excerpt of what was a very long facebook post:

[start rant]

I have been looking for some time at various strategies to increase the power of an R65,I have heard both the success stories and I have heard the disasters. Firstly I'd like to comment on the bad outcomes. The R65 has EXACTLY the same gearbox as its larger siblings, the final drive box is made of the same metal and has the same sized bearings as the larger bikes, so any drive line failures would probably have happened anyway.

Next if you look at the R65 engine, the oil pump is the same, the crank bearing sizes are the same, the cam chain is the same. In fact the only real differences are the crank throws (shorter stroke), conrod lengths, cam followers (different design to allow deeper contact with the pushrods to lessen the articulation angle. Anything else is merely a dimensional change of a well proven, soundly engineered part. So what is the problem with capacity increase kits?

Until the relatively recent arrival of the SiebenRock kit the general way was to machine down the length of a set of R90/100 barrels and either use slightly altered R65 heads or R75/80/90/100 heads. The big problem with all of this is that the longevity was utterly dependant on the machining skills of the person modifying the new componentry. There was also considerable reliance on the skills of the person doing the assembly, they had to know what they were doing, how to measure and how to further modify the various components for the correct fit.

After having had discussions with people who proceeded as above I have formed the opinion that in many builds that ended badly either the machinist or the assembler lacked crucial skills/knowledge. Of course I have NEVER heard anyone say "I screwed up because I didn't know what I was doing" so it was invariably the fault of the kit or some unspecified inherent fault in the R65 engine that turned what should have been a triumph into disaster.

In a word - BULL$HIT!.

Enter Messrs Siebenrock's kit - specifically engineered so that not too much actual mechanical/engineering skill is required to screw it together. But people still report failure. But then some people cannot manage a top end refresh using stock components as the number of lubrication failures from things such as blocking the flow through the upper studs or fitting the rocker shafts upside down attests.

My own view is that it is a little gung-ho to subject an engine that is at least 30 years old to a 32% capacity increase without at least inspecting crank and rod bearings, camshaft, followers, rockers and valves. Yet people continue to buy Siebenrock's kit online and spend a Saturday bolting it all up and then wonder why the end result was less than stella. 

Some legitimate concern was initially raised regarding the squish arrangements of early kits, the piston crown being not well matched to the heads but that is in the past with the current pistons in the kit specifically designed to match the R65 heads.

[end copied rant]

And so it went on and on... The take home is that I discount anyone's tale of woe if they didn't do a complete engine refresh prior to fitting.
  

1978 R100RS| 1984 R65 | 1984 XT350 | 1992 KLE500 | 2002 R1150GSA
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Semper Gumby
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Re: K100 Front end rebuild
Reply #12 - 06/07/18 at 12:42:45
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I believe your conclusion to your rant is correct: one musts refresh the motor. With 132,000 miles on the original gearbox and motor I am loath to change anything. But if I did this then the motor internals would all get rebuilt and inspected.

For me I was just regurgitating past lore. There has been this general conclusion that R65 bottom end is not suited to up grades unless care is taken to make sure the pistons are of a similar weight to OEM. The R65 has a shorter stroke and a higher redline than the long stroke R75/80/90/100.

I believe the relation ship to of piston velocity and the weight of the moving parts to redline is linear and limiting. If i was to do a bolt up kit, with no other information to go on, I would measure the weight of the piston, wrist pin and rings, and if they were different (I.e. more than stock) then I would crunch the numbers and come up with a new redline. This would be prudent and good to know.

As of yet I know of no documentation of an R65 in long term test of one of these kits. So I say caveat emptor as always. Cool

When you do this install Tony, could you measure carefully for the rest of us the parts (new and old in grams) so that we can see what is going on? That would be invaluable information.

And thanks in advance.

I will take the handlebar bits to a trailer shop and see if I can find similar urethane bits...
  

Bill Gould 1980/03 R65 When at first you don't succeed....Moo!
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Semper Gumby
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Re: K100 Front end rebuild
Reply #13 - 06/12/18 at 21:24:08
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Semper Gumby wrote on 06/06/18 at 16:23:47:
Tony!

If you could tell me the part number for the urethane trailer Bush it would save me some time for the handlebar mount. I would be in your debt.

I zip tied the lowers. If you makes two plates I will pay you for your time. Cool

Woo hoo. You did the r860 cylinder piston install. I must read about this. I saw them the other night. Bit worried about blowing out the bottom end making too much power....


TONY - I don't need the plate.  I zized wheeled my headlamp bracket in half to make room for the new faring mount.  If you have already made let me know and I'ii send some paypal.

It's mounted up to with two new holes and about 6mm of washer spacers to keep the headlamp bracket off to upper triple tree.  I'll take some pics tomorrow.

Shocked
  

Bill Gould 1980/03 R65 When at first you don't succeed....Moo!
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Semper Gumby
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Re: K100 Front end rebuild
Reply #14 - 06/13/18 at 09:09:59
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Tony -  one of the things you must do on this conversion is weld 5/8 bung on the front for a steering stop.  You. An see how I e cut away the plate.

  

Bill Gould 1980/03 R65 When at first you don't succeed....Moo!
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