'87 K-100LT - electrical problem

[Pier]

Hello everyone,

 

I'm looking for some help if anyone can suggest anything to solve my puzzle.

 

My K-100LT, which by the way ride everyday for the past six years, few days ago started giving me some electrical problem and I haven't figured out what it is yet.

 

When riding front and back lights blinks intermittently. Yesterday, after I got to work and parked, the starter wouldn't even move and the front and rear lights kept going on and off. If the radio is turned on I would hear loud statics cracking when the lights intermit.

 

Yesterday i started the bike downhill by engaging the secong gear, and after that it has always started right away, but lights still blinks. Sometime lights stay off for few seconds and then come up again. This season I ride on dayliglt so it is no problem.

 

Last winter I had similar problem and I fixed it by cleaning with sand paper the hot cable's terminal attached to the starter. I tried the same this time but although the engines starts at first try, the lights still blinks.

 

A Harley rider who works with me told me that he hasd similar problem with his Harley and he said that once he replaced the battery the problem got solved. The puzzle is that the battery seems still powerful because (with the exception of the other day ) the engine starts strongly.

 

I could try to replace the five year old battery but I doubt that is the solution to the problem.

 

Anyone has any suggestion?

 

Thank you,

 

Pier

[duckbubbles]

Hi Pier

 

You are are probably not going to believe me, but that happened to me. I have an older K100RS and I think the electrical systems are quite similar.

 

Try rebuilding or replacing the starter with a new/low mileage one. My local BMW tech told me that the lighting system grounds through the starter brushes. Try to find that one on the schematic!! They get worn or built up with carbon dust and don't conduct like they should.

 

My starter never quit working, but the lights would blink off and on and drove me crazy for a couple of weeks.

 

Frank

[kioolt]

I didn't even half to read all of your message to know what the problem is. It's not exactly true that the lighting system grounds through the starter but that is an easy esplanation. The load shed relay grounds through the starter. The load shed relay purpose is to cut power to all unnecessary electrical load when starting the bike. Lights, radio, heated hand grips and etc are turned off when starting. Your starter is your problem. It can possibly be disassembled and cleaned. I notice that you live in Fairfax, VA. I am in Bel Air, MD. If you could bring it to my house I can probably get it going for you for little or no cost. If a simple cleaning will not take care of your problem I have a starter that I rebuilt that we can put on. PM me if you are interested.

[bmwmick]

+1 A good disassembly and cleaning of the starter commutator should get you going.

 

Mick

[RFW]

You have a bad ground in the system somewhere.

 

RFW's Golden Rule of Electrical Engineering (and I AM an electrical engineer!) is as follows...

 

If something weird is going on, and several completely unrelated things are acting up, in unpredictable ways, the problem is grounding!

 

The loud static on the radio is further STRONG evidence of a bad ground.

 

The reason the starter is not operating is not because of the starter itself. It is because the starter relay (located in the electrical box with much of the rest of the electrical components) is not being actuated.

 

Check the chassis grounds (including the ground lugs bolted to the frame member under the tank).

 

Check the 2 connectors that plug into the back of the instrument cluster. Much of the bike's electrical system feeds into the instrument cluster, and these connectors have been known to cause weird problems. Generally, just plugging them in and out a few times will eliminate any film of corrosion that might be on them. It is a good irea to coat these connectors with a little Vaselene petroleum jelly (NOT REGULAR GREASE!), or silicone grease.

 

In particular, ensure that the motor mount bolts are tight and corrosion free, since these establish the ground to the engine. Also check the battery negative cable to the transmission (near the bottom left side of the battery).

 

In general, go around the entire bike and make sure all electrical connectors and especially ground lugs are tight and corrosion free.

 

There are too many unreated, oddball problems here for this to be anything else, except a grounding problem.

 

Bob.

[RFW]

+1 A good disassembly and cleaning of the starter commutator should get you going.

I disagree. A bad commutator can not cause static on the radio when the bike is running (and the starter is not), and it will not cause lights to flash.

 

Focusing on the starter in this case, is a little like saying that if there is smoke coming out of your muffler, the solution is to replace the muffler!

 

With any problem where multiple "strange things" are going on, it is important find the common thread. See my previous post on this.

 

Bob.

[Boffin]

+1 A good disassembly and cleaning of the starter commutator should get you going.

I disagree. A bad commutator can not cause static on the radio when the bike is running (and the starter is not), and it will not cause lights to flash.

 

Focusing on the starter in this case, is a little like saying that if there is smoke coming out of your muffler, the solution is to replace the muffler!

 

With any problem where multiple "strange things" are going on, it is important find the common thread. See my previous post on this.

 

Bob.

 

Yes it is a bad ground. To the load shed relay, which grounds through the starter on these bikes. This is a long-standing known issue with a known fix - clean the starter commutator.

 

Andy

[bmwmick]

Hi Pier

 

You are are probably not going to believe me, but that happened to me. I have an older K100RS and I think the electrical systems are quite similar.

 

Try rebuilding or replacing the starter with a new/low mileage one. My local BMW tech told me that the lighting system grounds through the starter brushes. Try to find that one on the schematic!!

 

Frank,

It's pretty easy to see why his starter relay and the load-shed relay are not grounding properly on this diagram:

http://web.inter.nl.net/users/BMW-K100RT-page/manual/wire_diagrams/k100RS_RT_LM.htm

The BOTH find their ground through the starter commutator.

The very first thing he should do is remove and clean the starter.

Mick

[RFW]

Yes it is a bad ground. To the load shed relay, which grounds through the starter on these bikes. This is a long-standing known issue with a known fix - clean the starter commutator.

Good point. Thanks, Andy. I must say that I still remain dubious about the radio static, depending on what he actually means by "static". If it is true static that occurs on an otherwise normally-operating radio, then I cannot see this as being caused by the radio's power being switched on and off by a chattering load shed relay. On the other hand, if by static he means the radio actually cutting in and out, then there's no doubt that the problem is as you have described.

 

Bob.

[Boffin]

Yes it is a bad ground. To the load shed relay, which grounds through the starter on these bikes. This is a long-standing known issue with a known fix - clean the starter commutator.

Good point. Thanks, Andy. I must say that I still remain dubious about the radio static, depending on what he actually means by "static". If it is true static that occurs on an otherwise normally-operating radio, then I cannot see this as being caused by the radio's power being switched on and off by a chattering load shed relay. On the other hand, if by static he means the radio actually cutting in and out, then there's no doubt that the problem is as you have described.

 

Bob.

 

The other thing that can cause static here is the poorly grounded wires in the harness. They can pick up ignition noise and re-radiate it at high enough power to be picked up by the antenna. That said, a more likely route in would be via the power lead, again poor ground can allow that to pick up noise and conduct it in. If there were no other issues, the first place I look for static on a radio is the antenna ground - easily overlooked but the cause of many noise problems.

Unintentional signal broadcasting from poorly grounded systems can be so usefull in my job......

 

Andy

[kioolt]

There's no doubt in my mind that IT IS the starter. Like I said in a previous post the load shed relay which switches power to the radio, lights, and other accessories. When the starter brushes get worn or excessively dirty the load shed relay will turn on and off. Rapidly sometimes. This will cause noise in the radio. I know I had it happen to me through my intercom system. I'm not an electrical engineer but I have been an electrical troubleshooter for about 30 years.

 

For the electrical engineer in the discussion here is an explanation of how the load shed relay coil is wired. The positive side of the coil is hooked up to the plus side of the battery through the ignition switch. The minus side is tied directly to the starter plus side. When the starter is at rest you have continuity through the brushes to ground for the load shed relay. Since the relay coil is such high resistance compared to the starter motor practically all of the battery voltage will be across the starter relay coil thus engergizing the relay turning on the light and other accessories. When the starter button is pushed the starter relay engergizes sending 12 plus to the plus side of the starter. Remember I said the load shed relay minus side is hooked up to the plus side of the starter. When this happens you have plus voltage on each side of the load shed relay thus de-energizing it which will then shed the load to give more power for the starter.

[RFW]

For the electrical engineer in the discussion here is an explanation of how the load shed relay coil is wired.

Yes, that was me. I am familiar with the grounding of the relay coil via the starter. This is exactly the same bit of cleverness that many Bosch automotive starter solenoids use to control one of the solenoid's two internal windings. Problem is, when I wrote my previous post, I had forgotten about the load shedding relay entirely.

 

Good call.

 

But as I wrote earlier, I was also puzzled by the original poster's comments on radio static. To me, static meant interferance, not a radio that is rapidly being switched on and off by a chattering relay.

 

It'll be interesting to see a report of the real "fix".

 

Bob.

[Pier]

Thank you very much to everyoone for your thoughts and suggestion. Because I had a 5 years old battery, today I went to buy a new one. Replaced the battery and the problem is still there. Now the stater does not turn and the front and rear lights do not turn on when I turn the key. I only see the lights on the instrument panels. I have been reading all your posts and at this moment I believe the problem lay on the starter. I still don't understand why the lights go on and off intermittently when the engine is running considering that the starter is not running, but I'm sure there is an explamation for it.

 

About the radio: If I leave the radio turned on, when the lights go on and off intermittently I can hear the speakers cracking very loud; in fack, I don't even hear the radio anymore when that happens, so now I turned the radio off.

 

Well, I still don't know how I will get the stater off and either try to clean or replace the brushes, but this will be my next step.

 

Right now if i want to go in anywhere with the K-100 I have to push it to start. When it start it is not a problem because I will not ride at night.

 

I will keep you posted on the fix. I have two more nikes and I'm suppoed to go for a 5K miles ride in two weeks. I really hope I can fix the K- commuting bike before that. In any case i will keep you posted on fix.

 

Thank you all again.

 

Pier

 

b_pier@hotmail.com

 

http://community.webshots.com/photo/446190833/1462816422078004862JcsRtq

[duckbubbles]

Pier-

 

The starter is located above/behind the ingition coils on the laft side of the bike, on top of the transmission. It is held in place by two 5mm screws and is plugged into the back of the engine with an o-ring to seal off oil. There is one wire connection on it.

 

The consensus is that if you get the starter fixed, new brushes, or clean the brushes and commutator, the problem will be fixed. This should take care of all the paoblems you are having with the lights and starting. Probably even the radio.

 

Good luck.

 

Frank

[Pier]

Unfurtunately I was only able to read all these post about an hour and a half ago, but once I finished reading I couldn't resist to start dealing with the started immediately.

 

So, in about 75 minutes I was able to take off the starter, open it completely and clean the brushes and the copper coil where the brushes touch, with very fine sandpaper, mount it everything back and start the bike.

Problem solved, at least for the time being. I even installed a new rubber ring that I found in my workshop. I tried startinmg the bike several time with no problems at all.

 

However, I noticed that on brush was considerably shorter than the other one. One was about 1/4" long and the other one only about 1/8". My feeling is that the problem may reoccur in the future but now I'll watch out for a used starter when I see a fair deal.

 

I just want to thank you all very much for your help. Today I spent more than three hours in the Washington DC area's traffic to go to the BMW dealer to buy a new battery. Had I read all thse post earlier I could have saved myself three hours and $95. Well, my battery was about 5 years old so it would have died very soon anyway.

 

You have all a great weekend.

 

Pier

 

 

 

[duckbubbles]

Good job, Pier!

 

From the measurement you said, I would say that the brushes are almost worn out. The new BMW part numbers for the brushes are 12411459295 and 12411459567. They are not too expensive and you should replace them before too long. You don't have to buy a starter as all the separate parts are available.

 

Good going- Frank

[kioolt]

I'm going to agree with duckbubbles that your brushes are worn out. If you were able to take the starter apart and clean it you should have no problem replacing the brushes.

 

I bought a starter on eBay about a year before I actually needed one. I knew that I was going to keep the bike practically forever and since it had almost 100k on it at the time I knew that I would need it someday. I seem to remember that I got it for around $20. When my original starter started doing the same thing yours was doing I use my eBay starter to get going. I then went to Bob's BMW and bought brushes for my original starter. So I now have a spare starter again.

 

If you decide to buy a starter on eBay you can use one from any K75, K100, K1100 or K1200RS but not the K1200LT. They are all the same.

[Pier]

Thank you for the info about the starter. I didn't know that many models use the same starter, including the K-1200RS.

While trying to unscrew the two bolts to open the starter I busted the phillips head of one of the two screw. In order to reuse the screw I had to cut the head in the middle with a metal saw so I could tight it in with a regular screwdriver. So now I would need the two brushes plus a new screw. No less than $30-40 at Bob's I suspect.

 

Thanks,

 

pier

[bmwmick]

Pier,

Congrats on the fix.

If it happens on your trip, here is a tip that might help, put the transmission in gear (2,3,4,5)with the engine off, clutch engaged and bump the engine backwards by pushing the bike backwards just engough to nudge the engine. This causes the starter to be rotated just a hair and it 'may' clean up the brush-to-commutator contact area enough to allow it to work for a while.

Mick

[duckbubbles]

That trick can also be applied to high mileage bikes that are starting to have starter sprague problems with oil sludge buildup. In that case, the starter spins but isn't turning the engine over. My K100 engine started doing that after about 180,000 miles.

 

Frank

[Dennis Andress]

However, I noticed that on brush was considerably shorter than the other one. One was about 1/4" long and the other one only about 1/8". My feeling is that the problem may reoccur in the future but now I'll watch out for a used starter when I see a fair deal.

 

Without reading this entire thread I am going to jump in a suggest you replace the brushes. BMW sells a resonably priced kit with two brushes and the plate they attach to. I once cleaned my starter only to have the problem return -- on a cold day in desolate West Texas.

 

Dennis