Author Topic: 1985 K100RS start mystery (Read 36117 times)

Lawrence · « **on:** October 27, 2011, 11:00:59 PM »

After work tonight I tried to finish the last "little" tasks subsequent to lubing the splines on my K100RS. I discovered in now refuses to start. When the ignition is on, the instruments are lighted but the starter simply makes an odd sound, and very faint at that. I first thought the battery was kaput after sitting about 10 days with the help of the trickle charger. Then I noticed that, even with the ignition off, the headlight (only) was on. What the *%!# have I screwed up now? Have I mixed up the connections to the battery posts? Fried an extremely expensive electrical wigget? The cabling to the battery seemed very simple and straightforward and I didn't bother to label them. Mistako!
The bike has one smallish cable that seems to exit the bottom of the airbox, and a a large gauge (starter?) cable that is in a sheath with another smaller cable. Both of these I attached to the positive post. The only cable on the negative post is the amazingly small ground cable. Are those the proper wiring connections?
On the other hand and if I'm lucky, maybe its just a dying battery that has caused this mystery. I disconnected the ground and hooked the battery to the trickle charger; the red light illuminated straight away telling me the battery is weak. But could this explain the headlight remaining lit?
Some ideas of where to go from here, please.

johnny · « **Reply #1 on:** October 27, 2011, 11:38:31 PM »

freakadelic there lawrence

pictures are our friends here at motobrick.com...

a photo of your battery and how you gotts it wired would be helpful...

j o

Lawrence · « **Reply #2 on:** October 27, 2011, 11:57:18 PM »

Okay, I'll try to post a pix of each battery post. Note the cables attached with the colored (red, black) flags are for the pigtail that I use for the trickle charger. That's the only cable I can be certain is correctly connected.

Lawrence · « **Reply #3 on:** October 27, 2011, 11:59:49 PM »

And then the positive post ....

johnny · « **Reply #4 on:** October 28, 2011, 12:17:00 AM »

im at work... using my phone... i can not see the battery...

im thinking 1 unobstructed overhead shot of the battery is what i need for the phone...

sorry...

j o

kennybobby · « **Reply #5 on:** October 28, 2011, 12:21:03 AM »

And what is the damn battery voltage? If you measure it with a voltmeter it can help you determine many things about the problem...but ya gotta have some data.

johnny · « **Reply #6 on:** October 28, 2011, 12:33:37 AM »

lawrence...

are sure you didnt turn the key to far ccw to the parking light position...

j o

Lawrence · « **Reply #7 on:** October 28, 2011, 09:26:25 AM »

The damn battery measures 12.6v at the terminals. My camera's batteries decided to die, so I can't provide an unobstructed pix from above the battery just now. As for the key position in the switch, I turned it as far as possible counter clockwise and the headlight remained illuminated. It only went out when I disconnected the ground wire.
The bike started easily before I disassembled the rear half to lube those pesky splines. When I have a mechanical issue, I have found it productive to check the last thing I did to the bike -- thus, the question about the connections to the battery. In essence, my question is this: On a 1985 K100RS that is bone-stock other than a pigtail for a battery charger, should there be any cable other than the ground strap connected to the negative post of the battery? The wiring diagram in the owner's manual indicates no, but I've grown suspicious of BMW docs of late. There are some inconsistencies.... hence my question to this forum. Thank you.

kennybobby · « **Reply #8 on:** October 28, 2011, 10:29:16 AM »

No other cables connect to the battery negative terminal except the ground strap/wire that runs to a [~~lock-tited~~]socket-head cap screw on the left rear side of the [transmission] housing in the region above the footpeg. Don't try to remove that cap screw--they intended for it to be permanent.

Your damn battery is not fully charged-- the voltage should be 12.8 or higher. The static surface charge on the plates can give a reading of 12.6 making you think it might be okay, but when it is put under a load (headlights, starter, fuel injection, etc.) the truth will be revealed. Connect the voltmeter and watch what happens to the voltage when you turn on the ignition switch and headlights, then what happens when you pop the starter button. If it gets pulled down below about 10.5 then it is suspect and on it's last legs.

frankenduck · « **Reply #9 on:** October 28, 2011, 10:31:57 AM »

Quote from: johnny on October 28, 2011, 12:33:37 AM

lawrence...

are sure you didnt turn the key to far ccw to the parking light position...

j o

JO: The two valve Ks have a different ignition switch than the 4 valvers.

frankenduck · « **Reply #10 on:** October 28, 2011, 10:38:29 AM »

Quote from: kennybobby on October 28, 2011, 10:29:16 AM

No other cables connect to the battery negative terminal except the ground strap/wire that runs to a lock-tited socket-head cap screw on the left rear side of the motor in the region above the footpeg. Don't try to remove that cap screw--they intended for it to be permanent.

If yours was Loctited then it wasn't done at the factory. I've pulled apart/serviced tons of Ks and never found Loctite there on a single one. It's not meant to be "permanent."

It bolts to the left side of the transmission, not the engine block.

Quote

Your damn battery is not fully charged-- the voltage should be 12.8 or higher. The static surface charge on the plates can give a reading of 12.6 making you think it might be okay, but when it is put under a load (headlights, starter, fuel injection, etc.) the truth will be revealed. Connect the voltmeter and watch what happens to the voltage when you turn on the ignition switch and headlights, then what happens when you pop the starter button. If it gets pulled down below about 10.5 then it is suspect and on it's last legs.

12.6V is more than adequate to start a bike. As I mentioned earlier, it's the cranking amps it can put out that matter more so load-testing is the only reliable way to test battery health.

frankenduck · « **Reply #11 on:** October 28, 2011, 10:51:36 AM »

Quote from: Lawrence on October 28, 2011, 09:26:25 AM

On a 1985 K100RS that is bone-stock other than a pigtail for a battery charger, should there be any cable other than the ground strap connected to the negative post of the battery?

The only thing on the negative post is the ground cable to the left side of the transmission. While you have the battery cables off it's a good idea to hit the cable terminals with some coarse steel wool or a metal brush to clean them off to improve their conductivity.

frankenduck · « **Reply #12 on:** October 28, 2011, 10:57:50 AM »

Quote from: Lawrence on October 28, 2011, 09:26:25 AM

As for the key position in the switch, I turned it as far as possible counter clockwise and the headlight remained illuminated. It only went out when I disconnected the ground wire.

This is very suspicious behavior. Does you bike have headlight relays installed? (They would not have been installed by the factory but it's a common owner mod.)

Lawrence · « **Reply #13 on:** October 28, 2011, 02:15:06 PM »

I've never removed the fuel tank and traced the wiring to the front of the bike. However, I have to believe that if there was a headlight relay, there would have been more cables to attach to the battery posts. (I have order a headlight relay from Eastern Beaver just this week). After work today I will remove the battery and take it to get a load test. I don't know if I want it to pass or not ::) If it passes, that means a continuing mystery in the electrickery; if it fails, I'll have to pony up for a new battery :-\
Sure would like to put some miles on her before it becomes much colder....

frankenduck · « **Reply #14 on:** October 28, 2011, 02:16:33 PM »

A lot of people (smart guys like me for example) power headlight relays in the relay box at the power input terminal for the starter relay.

johnny · « **Reply #15 on:** October 28, 2011, 02:24:23 PM »

and smart people con others into loaning out their catz azzure white 4100k 55/60 cause it blows away their chinese junk thats hooked to their starter relay...

j o

frankenduck · « **Reply #16 on:** October 28, 2011, 02:41:24 PM »

Quote from: johnny on October 28, 2011, 02:24:23 PM

and smart people con others into loaning out their catz azzure white 4100k 55/60 cause it blows away their chinese junk thats hooked to their starter relay...

j o

Dude, whenever the Big Brain lets you come back down here we'll go out at night and my $4 90/100 Chinese Xenon will make your Catz ch1t look like kitty litter.

kennybobby · « **Reply #17 on:** October 28, 2011, 06:08:42 PM »

Quote from: Lawrence on October 27, 2011, 11:00:59 PM

subsequent to lubing the splines on my K100RS.

Did you happen to remove the ground strap on the transmission when you did the spline lube?

Lawrence · « **Reply #18 on:** October 28, 2011, 07:37:58 PM »

Well yes, of course I disconnected the ground wire. I don't know how to lube the splines without removing the battery and....
Upon return home today, I measured the volts across the battery posts again. 12.9. When I did the recent spline lube, I cleaned all the electrical connections I came across - contact cleaner and wire brush stuff. I'm convinced the battery is strong enough to start the bike. I don't believe this is an insufficient power issue. There's something else going on here. The moment I connect the - lead to ground, the lights come on (instruments, headlight) yet the bike's starter will not operate. I suspect the ignition switch. How can I test it?
I'm hoping there's a simple (read: stupid) mistake I made while learning to lube the splines and not some exotic and expensive component failure at the bottom of this problem.

kennybobby · « **Reply #19 on:** October 28, 2011, 09:14:59 PM »

Edit 2: BrickFlyer has a great link with excellent info in the following post. i have swiped part of Bert's troubleshooting image and added it here to my message.

Edit 1:The load-shedding relay contacts have to be closed for power to reach the headlight. That could happen for two reasons: [1] the relay contacts are welded together, or [2] the ignition switch contacts are shorted, thereby sending power to the relay control coil which is grounded thru the starter motor and pulls the relay contacts closed.

The most likely candidate is [2] due to a dirty or broken ignition switch, but to determine which it is

i would remove the negative ground wire at the battery, and then remove the fuel tank. Trace the wiring harness from the ignition switch down to the right side of the frame to where it enters the electrical box--there will be a four pin connector in that harness. Disconnect the 4-pin inline connector and reconnect the ground wire to the battery. If the headlight comes on then the relay contacts are welded together. If not then the ignition switch is the culprit.

BrickFlyer · « **Reply #20 on:** October 28, 2011, 09:48:57 PM »

<<I suspect the ignition switch. How can I test it? >>

Here's a link that I found helpful when troubleshooting the electrical system on my 85 K100RS.

http://hrsbstaff.ednet.ns.ca/bvogel/K100/download/bike-wont-start1.htm

Inspecting and cleaning the ignition switch is not that tough. I was glad I did it on my bike since I found that several wires were down to a few strands and most of the insulation had rotted.

To remove the switch you just remove the fasteners holding the rubber housing that the ignition switch sits in, then take off the bezel ring around the ignition switch which will expose I think three little slots around the circumference of the switch. These slots let you access some little plastic tabs that lock the switch into the hole. Once the tabs are pried back you push the switch out the bottom if I recall correctly. Don't overdo it as you could break the tabs entirely if you are too aggressive. The article below will give you a feel for what I am talking about.

Then you can inspect the wires and use an ohmmeter to check the contacts. You can also disassemble and clean the ignition switch even though BMW says there are no user serviceable parts inside. That task is documented here:

http://ibmwr.org/ktech/ign-switch-disassemble.shtml

I cleaned all the contacts with CRC, lubed it with dielectric grease and it popped back together.

Your problem and symptoms are different than the issue I was chasing, but if your 26 yr old wiring is as bad as mine was it may prevent a future issue.

pallum · « **Reply #21 on:** October 28, 2011, 10:36:03 PM »

+1 BrickFlyer

Edit: wrong thread, but sound sound advice from BrickFlyer

wmax351 · « **Reply #22 on:** October 29, 2011, 03:34:15 AM »

Just read this over. You may be hearing the fuel pump running, rather than a starter. Kind of a whir/buzz.

What you should do is take jumper cables from the positive terminal and touch them to the starter terminal. You may have a dirty or worn starter. If it doesn't crank the starter with a know good battery hooked to the terminal (Behind coils), that is the answer.

You can also try putting it into 5th, and backing the bike up to turn the starter to a different place on the commutator. Or try bump starting it.

The starter stuff can cause other weird things. The load shed relay is grounded through the starter motor. If the commutator or brushes are worn or dirty, it can cause all sorts of problems.

johnny · « **Reply #23 on:** October 29, 2011, 11:36:04 PM »

CRASH · « **Reply #24 on:** October 30, 2011, 03:24:59 AM »

Quote from: johnny on October 29, 2011, 05:36:04 PM

ROFL ... perfect.

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Author Topic: 1985 K100RS start mystery (Read 36117 times)