1991 K100RS 16V - Starter/Ignition Switch/Relays/Ground issue?

[WHITE91K100RS]

Hello all,

Longtime lurker, first time poster here. Hoping you would all be so kind as watch this short video of my 1991 BMW K100rs 16v and help me diagnose this wonky issue I’m having with my starter/ignition switch/starter relay/load shed relay?

When key is turned, headlight intermittently comes on. While starting the bike, the starter kind of ‘chugs’, sounds almost like it is being turned by the engine.  If the bike does start, the headlight goes out. I’ll hit the kill-switch and try to start bike again, and it won’t start (hear click, I believe is the starter solenoid opening and closing). You can see this in the youtube video linked below.

I thought maybe it was a dirty starter commutator or burnt out starter brushes. Took the starter out, cleaned it, replaced one of the brushes which was significantly more worn than the other. Reassembled starter. I also purchased a new (aftermarket) battery. Unfortunately, the problem still persists. My next thought is to clean out the ignition switch because I understand that carbon buildup in there can cause these same problems. Unfortunately, the 1991 K100 has the ignition switch housed in the triple-tree, and I need to drill out the ‘security-bolts’ to get in there, or so I'm told (so, I haven’t dug that deep yet)

Please see short video of described symptoms here:


Any thoughts?

[kioolt]

I watched your video.  Despite the fact that you cleaned and replaced one brush in the starter it still looks like a starter problem.  It would be real simple to determine with a voltmeter.  Place the voltmeter on the starter terminal while pressing the start button.  If you have battery voltage there and it isn't starting then IT IS the starter.  You can get a voltmeter at Harbor Freight for about $5.

[WHITE91K100RS]

Hey, thanks for taking the time to help me diagnose this bugger.

Yes, I have a voltmeter.

While the new aftermarket battery was installed (and when that video was filmed 2-3 days ago) I metered 12.6 at the starter terminal before starting. I did not however meter at the terminal while the starter was engaged (doh!).

I expect to have a BMW installed in the bike this weekend so I can do some more troubleshooting. Until then, I wanted to clean up the ignition switch, but that has proven difficult with it's location in the triple tree. I think I'm just going to squirt some Deoxit contact cleaner in the key hole and hope that sufficiently cleans the ignition switch (ya..?)

[TimTyler]

I don't think the problem is in the key switch.

Make sure the battery cables are in good shape and are tightly connected at both ends. Clean those battery and starter cable connections. Re-seat your connection to the alternator too.

Have a look here too http://hrsbstaff.ednet.ns.ca/bvogel/K100/download/bike-wont-start1.htm

[kioolt]

If you've got 12.6 volts at the starter under any condition and it is not running it is bad.  There is no need to do anything to your ignition switch.  The click you hear when pressing the start button is the starter relay.  That in itself shows your ignition switch is ok. 

[WHITE91K100RS]

If you've got 12.6 volts at the starter under any condition and it is not running it is bad.  There is no need to do anything to your ignition switch.  The click you hear when pressing the start button is the starter relay.  That in itself shows your ignition switch is ok. 

Ok, so that's good news for my starter relay and ignition switch then... no need to continue to troubleshoot there.

What should the starter terminal be metering before crank and during crank?

[kioolt]

The starter terminal should be very close to zero before cranking and very close to battery voltage when cranking.  I've never measured the voltage under either condition but my 35 plus years of being a professional electrical trouble shooter and what I know about the wiring on the K-bikes is what I am basing my answers on.  I went to trade school for industrial electronics and I have an Associate Degree in it.  After school I went to work as an electrician in several industrial plants where I did electrical trouble shooting, maintenance, and installation.

[WHITE91K100RS]

Well, now you have me thinking that when I metered the starter at the terminal I must have had the bike on (this was 2-3 days ago when I had a battery). I will confirm voltages when I have a battery installed, hopefully this weekend.

Also, I must add; Whenever the headlight is out and the starter relay clicks but bike is not starting (as seen in video linked above).... if I give the starter a whack with a wrench, it brightens up and the headlight comes back on. With the same symptoms, if I give the relays under the tank a whack with the wrench, the headlight comes on as well.

[kioolt]

I'm 99.99999% sure it's the starter.  Another test you can do is to put the bike in gear.  By rocking the bike forward and reverse you will probably get the headlight going on and off.  This is another indication that it is the starter.

[WHITE91K100RS]

I cleaned up all the grounds and hot terminals with a wire brush and contact cleaner, put a new BMW battery in there and problem solved. Thanks for your input fellow brick enthusiasts. safe riding