Author Topic: New old 1991 K100RS 4V  (Read 2514 times)

Offline riots100

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New old 1991 K100RS 4V
« on: July 23, 2018, 01:43:23 AM »
Found this 1991 K100RS 4V in southern Utah with only 7200 miles.  It is probably the closest that I'll ever be to getting a new K-bike. 







It looks practically brand new.  So we made a deal for the bike and picked her up this weekend and drove back to LA










It looks great in the right kind of light






It is a very clean bike down to the smallest of items
















It even came with the original dealer Standup plaque




The tires are almost brand new, all the rubbery components look and feel nearly new and the fuel pump/tank is in great condition.  The pre-purchase shakedown ride was uneventful and the cooling fan kicked on right when is should according to the temperature gauge.  Brake lines are flexible and crack free.

There are only two known issues with the bike:  the ABS doesn't work (ABS light is on) and there is leaky left fork seal.  Right above the leaky fork seal, there is a black smudge on the fork tube that will not clean off.




I want to fix the known issues, perform preventive maintenance for issues that this bike is known to have and then ride the heck out of it.

Known Issues:
ABS I fault light is on and ABS is non-functional - I will want to restore full ABS functionality on this bike.  I need to read up on ABS reset and fault codes to narrow down the likely culprit.
Leaky left fork seal - not bad, but it is there.

Preventative Maintenance:
Oil change - I was thinking of putting in 20W-50 Synthetic
Brake fluid flush and bleed - after the ABS fix
Large hose clamp near exhaust collector to prevent the known issue of cracking welds
Check air filter and if needed, replace
Change fork oil - after fork seal fix
Add Headlight relay harness from Eastern Beaver
Rear view mirror leashes
Side cover leashes

I would be interested in hearing thoughts about checking the splines on the drive shaft and final drive given the low milage and age of the bike.



  • Los Angeles, CA
  • 1992 K75, 2007 K1200GT, 1991 K100RS
----
BDJ

Offline Martin

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Re: New old 1991 K100RS 4V
« Reply #1 on: July 23, 2018, 02:59:47 AM »
Excellent pickup. :clap: Before you replace the fork seal try using a Seal Mate. They can be bought or made from a soft drink bottle. If the seals are hard try Jo's method, soak a rag in ATF and wrap it around the seal and let it soak.

Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Online Laitch

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Re: New old 1991 K100RS 4V
« Reply #2 on: July 23, 2018, 03:23:19 AM »
Brake fluid flush and bleed - after the ABS fix
Consider doing the flush, bleed and sensor gap check first. That might fix it.
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline Scott_

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Re: New old 1991 K100RS 4V
« Reply #3 on: July 23, 2018, 07:03:18 AM »
Congrats on the bike, it sure does look pristine.

At that age, I personally would consider replacing ALL of the rubber bits, fuel lines, brake hoses, vacuum lines, etc......
As far as the splines go, being a paralever bike the FD splines and transmission output shaft splines don't wear much if at all. The wear points will the the drive shaft intermediate spline(middle of shaft) and the clutch splines.
If you pull the transmission to check the clutch splines I would plan on replacing the clutch nut o-ring. If it isn't leaking now, it will shortly. Death of this o-ring is more related to age, not mileage.
Check the heatsink paste on the ignition amplifier, most likely dried up.
Not sure you may find 20-50 synthetic, but I've been using 15-50 and not had any issues.
As far as the ABS, it's possible that the motors and relief pistons/valve could be stuck from sitting for years.
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Ride safe.


1997 K1100LT 0302488
1995 K1100LT 0302044
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Offline rbm

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Re: New old 1991 K100RS 4V
« Reply #4 on: July 23, 2018, 07:10:07 AM »
Congratulations of finding a good specimen of a K100-4V.  Please please please resist the temptation to strip the poor girl bare and go at her with a cutoff tool.

The tires may look pristine however the rubber compounds used in their construction may have deteriorated and hardened.  Check the date code on the tires and, if they are greater than 5 years old, consider replacing the tires.  Bridgestone T30 Battlax 110/80ZR-18 front and 150/70ZR-17 rear are good choices for that bike.
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline The Mighty Gryphon

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Re: New old 1991 K100RS 4V
« Reply #5 on: July 23, 2018, 08:20:19 AM »
Boy, that's a really nice bike.  Are you going to build a cafe or a scrambler?  How much do you want for the fairing and belly pan when you strip it?

I'm with the other posters regarding the tires.  Hoses and other bits could wait until you have some miles on it, depending on how it was stored they may still have a fair bit of life left in them.  Definitely change all the fluids, especially the brake fluid.  It may be necessary to run a couple quarts of DOT 4 through the system to completely clear out the old crystallized fluid.  With any luck, sitting in dry Utah will have prevented any corrosion in the rear master cylinder.  Just be gentle when bleeding to avoid damaging the rubber seals in the brake system.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '92K100RS White, '94 K75S Dakar Yellow
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'94 K75S "Cheetos"
'91 K100RS "Moby Brick Too

Online Laitch

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Re: New old 1991 K100RS 4V
« Reply #6 on: July 23, 2018, 08:51:45 AM »
Your moto has a Euro headlight switch on the right side, too. You might some German spec model components, based on this video from Chris Harris.
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline riots100

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Re: New old 1991 K100RS 4V
« Reply #7 on: July 23, 2018, 09:56:14 AM »
Boy, that's a really nice bike.  Are you going to build a cafe or a scrambler?

I am not going to turn this machine into anything other what she already is.  It will remain a stock BMW K100RS 4V.  To do anything else to this pristine specimen would be an aesthetic travesty.  The only thing that I would consider doing would be to replace the fairing with one from an 1100RS.  I do like the look of that bike quite a bit.  Spec wise, the two bikes seem to be almost identical.  I also may replace the seat with an aftermarket one.

Although the Metzlers look in excellent condition, the date code is 3412.  So they look to be just over 5yrs. old.


Your moto has a Euro headlight switch on the right side, too. You might some German spec model components, based on this video from Chris Harris.

Yea I saw this video as well.  According to the video, the items on my bike that match the German spec are:
- headlight switch
- motronic connector color (white)
- power outlet plate (single outlet, aluminum)
- Bilstein rear shock

The video also indicates that the 1100RS fairing was an option for the K100RS.  So fitting the 1100RS fairing would keep the bike on the stock side of the equation.

If the seals are hard try Jo's method, soak a rag in ATF and wrap it around the seal and let it soak.

Where would I find Jo's fork seal restoration method in more detail?  It's worth a shot.
  • Los Angeles, CA
  • 1992 K75, 2007 K1200GT, 1991 K100RS
----
BDJ

Online Laitch

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Re: New old 1991 K100RS 4V
« Reply #8 on: July 23, 2018, 10:28:50 AM »
Where would I find Jo's fork seal restoration method in more detail?  It's worth a shot.
Read this and the entertaining and informative posts attached to it.
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline riots100

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Re: New old 1991 K100RS 4V
« Reply #9 on: July 23, 2018, 11:35:37 AM »
Read this and the entertaining and informative posts attached to it.

Entertaining and informative, I may have compromised the seal due to fork compression while trailering the bike. Rats.
  • Los Angeles, CA
  • 1992 K75, 2007 K1200GT, 1991 K100RS
----
BDJ

Online Laitch

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Re: New old 1991 K100RS 4V
« Reply #10 on: July 23, 2018, 11:47:04 AM »
Entertaining and informative, I may have compromised the seal due to fork compression while trailering the bike. Rats.
You might have, but the treatment johnny describes is possibly an antidote. Give it a try. It's next to effortless.
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline Chaos

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Re: New old 1991 K100RS 4V
« Reply #11 on: July 23, 2018, 11:58:42 AM »
Love the bike.  And it's a survivor, K1 in RS clothing. 
  • sw ohio
1987 K75S    VIN 0231
Original owner, Original litter
200,000 miles (plus or minus) and 5 paint jobs
2012 Ural 2WD sidecar (BMW's bastard step child)

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Re: New old 1991 K100RS 4V
« Reply #12 on: July 23, 2018, 12:36:28 PM »
Great looking bike, congratulations.


As well as the other things mentioned above I would fit mirror tethers to the mirror pods and another set to the glass.  Both these parts are now very hard to find and the mirrors have been known to pop off quite easily, my tethers have saved me at least four or five times.


I fitted a K110 RS faring and it is a pretty straight forward job.  I like the look of it as well but have to say now that I have owned the bike a while I am actually considering going back to the standard fairing, the look of the engine is growing on me I guess.
  • San Jose, Costa Rica
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Offline Skunky

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Re: New old 1991 K100RS 4V
« Reply #13 on: July 23, 2018, 03:21:50 PM »
Very Nice  :2thumbup:
  • Derby GB
  • BMW K100lt
Rebuild it and they will come..
90 K100lt
Triumph Thruxton 900
Honda CB400F

Offline riots100

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Re: New old 1991 K100RS 4V
« Reply #14 on: July 23, 2018, 06:46:25 PM »
Ordered the braided stainless steel brake line kit. 

measured front ABS sensor gap: 0.48mm (0.35mm - 0.55mm spec.) measurement falls within spec.
measured rear ABS sensor gap: 0.70mm (0.35mm - 0.65mm spec.)  seems to be a little loose, measurement falls outside spec.

I'm going to check the ABS diagnostic codes to see if it correlates with my observations.
  • Los Angeles, CA
  • 1992 K75, 2007 K1200GT, 1991 K100RS
----
BDJ

Offline The Mighty Gryphon

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Re: New old 1991 K100RS 4V
« Reply #15 on: July 23, 2018, 07:45:57 PM »
I put the 1100RS fairing on my bike as well.  Was very straightforward.  I only needed the lower panels with the knee pads and the belly pan.  I kept the original battery covers.  No big deal if you can't get the rear bracket for the belly pan, I made my own from a chunk of stainless sheet.  The rest of the mounts are the same as the old fairing.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '92K100RS White, '94 K75S Dakar Yellow
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'94 K75S "Cheetos"
'91 K100RS "Moby Brick Too

Offline riots100

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Re: New old 1991 K100RS 4V
« Reply #16 on: July 23, 2018, 08:24:44 PM »
I only needed the lower panels with the knee pads and the belly pan.

The knee pads are the black inserts that fit between the tank and fairings?
  • Los Angeles, CA
  • 1992 K75, 2007 K1200GT, 1991 K100RS
----
BDJ

Offline The Mighty Gryphon

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Re: New old 1991 K100RS 4V
« Reply #17 on: July 23, 2018, 08:29:48 PM »
Yep, there are some subtle differences between them in the lower attachment point that prevents you from using the earlier version.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '92K100RS White, '94 K75S Dakar Yellow
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'94 K75S "Cheetos"
'91 K100RS "Moby Brick Too

Offline riots100

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Re: New old 1991 K100RS 4V
« Reply #18 on: July 23, 2018, 08:54:53 PM »
Any one had any luck with Speed Bleeders as outlined here?
  • Los Angeles, CA
  • 1992 K75, 2007 K1200GT, 1991 K100RS
----
BDJ

Offline Skunky

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Re: New old 1991 K100RS 4V
« Reply #19 on: July 23, 2018, 11:02:20 PM »
What a speed bleeder does is stop the air from going back into the system when you release the brake. The same can be achieved by locking the bleeder before releasing the brake. The sequence should be as follows.

Loosen Bleed nipple a quarter turn - apply brake - tighten nipple - release brake - repeat until bubbles stop. You can do this on a bike because its all within reach.

However if you find it difficult to reach you could use a speed bleeder or an in line one way valve kit which are re-useable and half the cost of a Speed Bleed. Or less if you get one from China

https://www.ebay.com/itm/ONE-MAN-BRAKE-CLUTCH-BLEEDING-KIT-TOOL-BLEEDING-TUBE-ONE-WAY-VALVE-MLR-BME/123006758701?hash=item1ca3c62f2d%3Ag%3A8cAAAOSwm9JaoUWq&_sacat=0&_nkw=one+way+brake+bleed+&_from=R40&rt=nc&_trksid=m570.l1313

https://www.ebay.com/itm/Cars-Motorcycle-Brake-Bleeder-Clutch-Bleeding-Hose-Tool-Kit-One-Way-Valve-Tube/162890858838?hash=item25ed0d4156%3Ag%3AnYMAAOSwPkBaeroM&_sacat=0&_nkw=one+way+brake+bleed+&_from=R40&rt=nc&_trksid=m570.l1313



  • Derby GB
  • BMW K100lt
Rebuild it and they will come..
90 K100lt
Triumph Thruxton 900
Honda CB400F

Offline Skunky

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Re: New old 1991 K100RS 4V
« Reply #20 on: July 23, 2018, 11:10:31 PM »
I guess the advantage of the one way valve over the speed bleed is that you can see if there is still air in the tube before the valve where with the speed bleed its just guesswork.
  • Derby GB
  • BMW K100lt
Rebuild it and they will come..
90 K100lt
Triumph Thruxton 900
Honda CB400F

Online Laitch

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Re: New old 1991 K100RS 4V
« Reply #21 on: July 24, 2018, 05:33:07 AM »
I guess the advantage of the one way valve over the speed bleed is that you can see if there is still air in the tube before the valve where with the speed bleed its just guesswork.
If air is present in the system, it can be seen in the stream of brake fluid using the speed bleeder when the brake lever or pedal is pressed, just like when a standard bleed valve is opened then closed. When air is no longer visible, the bleeder is tightened and the fluid topped up. If the lever pressure is good the job is finished, just like when using a standard bleed valve. I have them mounted fore and aft. The speed bleeders cost me around ten dollars each as part of an Aerostich order years ago.

So far so good.
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline Barry in IN

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Re: New old 1991 K100RS 4V
« Reply #22 on: July 24, 2018, 02:30:53 PM »
That is just beautiful.  A time capsule and extremely versatile and useful motorcycle. 
  • Indiana
  • 1992 K75S Lili Von Shtuppe
A pox on cafe “builders”

Offline riots100

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Re: New old 1991 K100RS 4V
« Reply #23 on: July 26, 2018, 12:27:07 PM »
You might have, but the treatment johnny describes is possibly an antidote. Give it a try. It's next to effortless.

Cleaned up the forks and performed the Johnny treatment with ATF.  Rode the bike over the last couple of days and haven't observed any fork oil leakage.  Hopefully I dodged that bullet.
  • Los Angeles, CA
  • 1992 K75, 2007 K1200GT, 1991 K100RS
----
BDJ

Offline billday

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Re: New old 1991 K100RS 4V
« Reply #24 on: July 26, 2018, 10:06:24 PM »
Brother, we all look great in the right kind of light.

That is a beautiful motorcycle,  enjoy!
  • New York State, USA 10977
  • 1985 K100

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