My 1985 K100RS is alive!

[stevenm]

Hi all,
I recently purchased a 1985 K100RS, unmolested, with 18,000 miles.  After changing the oil and filter it went dead, as in dim dash lights, no response from the starter button at all.  Was scratching my head like a monkey.  Joined MOTOBRICK, read your tech articles, and it was the ignition switch, the one they don't make anymore.  Following your instructions, I rebuilt the switch, as well as tightened the starter relay cable, which for some reason was loose, and it started right up.  Can't say thank you loud enough.  I also changed the coolant, and noticed the fan did not come on.  Generally, how long is it supposed to take for the fan to come on for an idling K100?

[Laitch]

Welcome to Purgatory, stevenm!

Regarding the fan: Take a thin dowel or screwdriver and determine if you can move the fan blade easily. It won't spin like a roulette wheel but it should move without your straining or beating on it. If it does then it's likely to start up within 15 minutes of idling in the climate of beautiful Culver City. It'll run for a minute or so then shut off if you have sufficient good quality coolant in the system. If it doesn't, there are plenty of posts describing diagnostic procedures for locating the fault.

Good luck with your moto and enjoy the ride!

[stevenm]

Hi Laitch,

When I looked at all the wiring under the tank I thought I was in purgatory.  A lot more going on in there than my trusty and much loved R65.  The good part of going through this repair was getting familiar with the bike.  Glad it ran into trouble in my driveway instead of out on the road.

The fan spins smoothly.  I didn't want to overheat the engine but being new to it I'm not familiar with how hot it should get.

I plan to make is a foil faced cardboard dam between the radiator and the air boxes/fuel tank to smoothly lead the heated air to the right side vent.  Not really any room for that towards the left vent.  I've also read about insulating the fuel lines which seems like a good idea as well.

What my bike needs more than anything else is to have miles put on it. 

[Chaos]

In moderate climates the fan will rarely come on except at long traffic lights.  I was running around all summer with my fan froze up, just tried to stay moving.  I wouldn't recommend that but you'd be fine for short rides even if the fan was inoperative.

[natalena]

I plan to make is a foil faced cardboard dam between the radiator and the air boxes/fuel tank to smoothly lead the heated air to the right side vent.  Not really any room for that towards the left vent.
 

Using aluminum foil tape (for ducting/insulation) on pizza box cardboard works really well. I made a Johnny Blanket under the seat that way (pictures somewhere on site here) and it's made a huge difference in heat flow/transfer.

[stokester]

That's a nice looking survivor.

Good on you figuring out the problem after checking the site.
There is a great deal of information on the site and many members willing to assist.  It is always beneficial to add to the site knowledge as you have done, thanks.

[stevenm]

Took my K100RS out to warm up the gearbox and final drive oil.  Short drive, fresh gas, then stopped at my friend Steve Beck's Check Point Automotive in Mar Vista to show him the bike, and check out the museum quality very early real Cobra he was working on.  While idling, the fan came on!  Then as I rode away, it turned off.  One less thing to worry about.

Swapped out the gearbox and final drive oil with new BMW 80/90.  Ready for a shakedown drive up the coast early one weekend morning.

[natalena]

Swapped out the gearbox and final drive oil with new BMW 80/90.  Ready for a shakedown drive up the coast early one weekend morning.

Super cool to see an actual Cobra being wrenched. You've probably already done it with the fluid change, but lubing the FD splines before your trip is easy peace of mind. *Yellow House breakfast is always a good stop along the PCH north of Hell-A. Enjoy! :)

[stevenm]

Don't know if I will make it to Santa Barbara.  Maybe Ojai for breakfast.  Depending on what's going on with the fires...

Steve always has interesting cars in his shop: Cobras, GT350s, real GT40s, Gullwing Mercedes, etc.  And he's a factory trained BMW guy, so if the Jetronic goes south on my bike he will know how to deal with it.  He's a modern day Phil Remington.  Best shop in town.  I'll stop before I sound like a commercial...

[Cafe racer]

Get some miles on that BRICk and enjoy it

[volador]

Welcome SM

Very nice moto & low mileage, rarer color

Some links for your K journey

Just bought a 2V

Just bought a 4V

Check parts compatibility with BMW MAX Microfiche, BOBS BMW, REAL OEM

https://shop.maxbmw.com/fiche/PartsFiche.aspx

https://shop.maxbmw.com/fiche/PartsSearch.aspx

https://parts.maxbmw.com/BMW___BmwMotorradK.html

https://www.bobsbmw.com/store/microfiche/BrowseSeries.aspx

https://www.realoem.com/bmw/select.do?kind=M&arch=1

https://www.ascycles.com/BMW-Motorcycle-Parts-Fiche

Cross reference parts like Bosch pn#'s, etc....  http://partsplusecat.com/
No spaces in the part number

Parts Vendors

https://www.beemerboneyard.com/

https://www.capitalcycle.com/

https://www.euromotoelectrics.com/

https://www.tills.de/

Headlight relay stuff if you chose to add one

https://www.motobrick.com/index.php?topic=268.0

http://www.motobrick.com/index.php/topic,4962.msg30932.html

http://culayer.com/product/matchbox-headlight-relay/

http://easternbeaver.com/Main/Wiring_Kits/H4_Kits/h4_kits.html  Eastern Beaver site is a great reference for electrical connectors,plugs, etc...

http://www.k100-forum.com/

http://www.kforum-tech.com/Tech-page.html

http://www.kforum-tech.com/electrical/EFI/bike-wont-start-EN.htm

http://www.kforum-tech.com/Downloads/electrical/diagrams/interactive_diagrams.htm

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/k100tshoot/K100.Troubleshoot.Start.2018.pdf

http://kbikeparts.com/index.htm

http://www.kbikeparts.com/classickbikes.com/ckb.tech/ckb.new2k.htm

http://www.kbikeparts.com/classickbikes.com/ckb.tech/ckb.tech.toc.htm

http://www.eilenberger.net/K75S/IgnitionSwitch/

http://www.verrill.com/moto/moto.shtml

this site has a lot of good info and breakdown pictures in the tech and tech resources sections for K1100 alot of the parts are on K75 & K100

http://www.k11og.org/forum/index.php?sid=2df953dde5715fd9001fbe69edec5ad0

https://ibmwr.org/index.php/k-bike-tech-articles/

This site has all kinds of technical specifications on all the BMW models    http://www.bmbikes.co.uk/mechanicalpages/kseriesmechanical.htm

http://largiader.com

http://bmwk10075abs1fix.web.fc2.com/index.html  Toshi ABS site

Hosa D5S-6 CAIG DeoxIT 5% Spray Contact Cleaner, 5 oz.

CAIG Laboratories D100L-25C Contact Cleaner Needle Dispenser

Notable differences of the pre-85/86 K100 are the seat pan design with matching tail cowl section, the water/oil pump design changed, throttle cable design and fuel tank/fuel level sender/fuel return check valve.

Your '85 may have the European "hotter" cams known as "Finest Year K"

http://www.motobrick.com/index.php/topic,3653.msg21985.html#msg21985

https://forums.bmwmoa.org/showthread.php?4534-Why-is-the-85-K100-the-quot-Finest-Year-K-quot&s=66f149b3cadea44550d51fbf0b9ee793&p=42512&viewfull=1#post42512

The pre-1985/86 has molded pillion handles as part of the seat pan, metal or plastic seat pan.
Post-1985/86 removed handles from seat pan and added handles to the tail cowl section.

http://www.bmwkbike.dx.am/CLseats/kbikeseats.htm

Water Pump
pre-1986-87? original design old style impeller 11411461177

Superseded by 11412325850 design change the shaft with gear Z=32 teeth, shaft- 11411461183

Superseded by 11417676366 same shaft with gear Z=32 teeth

latest design 11517676371 design change shaft with gear Z=19 teeth, shaft- 11411461793

Throttle cables have 2 versions and lower brackets. Cable lengths vary with handlebars.
#1 version- have a adjustment sleeve approx. halfway down length
2nd version black plastic collar at the lower end or a white plastic collar

Pre-1985 fuel tank has a rear mounting tab later removed.
Early fuel lever sender is a thermistor type later is a float type.
http://www.kforum-tech.com/how-to/Modification%20for%20early%20gas%20tank.htm

Check condition of the inside of fuel tank. Lowest portions are prone to corrosion when moto is left sitting for some time.