BMW K bikes (Bricks)

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elementalfire

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This story is slightly long winded so please bear with me.

I have been enjoying my 1985 BMW K100 for the last three years and near the end of last season the bike just wouldn't start anymore. After a glorious 1800 km trip through northern Ontario and down the Bruce Peninsula I stopped for gas 80 km from home and my bike would not start. I couldn't bump start it, I could not get it to turn over so, I managed to rent a truck and bring it home to the garage where it sat and waited.

I called my closest BMW dealership 100 km west of here and they had no idea what it could be as they had never worked on a K100. So I started with the cheapest component in the starting system which was the starter relay. It took two months to get it from Germany and it was an aftermarket component, due to the lack of availability of OEM parts for this model and year. So I had to wait till the spring to start working on it again. I installed the new relay and reconnected the battery then due to my absolute brilliance I wired the battery backwards and fried the positive side of the wiring. I then ordered a replacement wiring harness as once again it is impossible to get anything for the K100 so that took several weeks. I then spliced the wiring back together and alas once the battery is connected the battery light and clock turn on but will not start or even get a clicking sound from the starter but the fuel pump does turn on occasionally. The starter appears to work as a jump start from the battery positive side to the starter wire connection gets it to turn but no kick.

The battery is fully charged, I have checked and rechecked the harness and all is connected solidly but the battery light turns on as soon as the battery is hooked up, I have installed the old starter relay and the new starter relay with the same results repeatedly. I have taken the starter switch apart and cleaned it thoroughly and the same results once again. All the fuses are in working order so, now I am at a loss as to what to try next and I'm getting sick of seeing other people enjoy their bikes while I sit in a shed cursing at my bike.

What should I try next?

Thank You,

elementalfire

    

Laitch

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Are you stating that the alternator warning light is lit when the battery is connected but without the ignition switch being turned to On?

Next time you need to disconnect the battery to replace another component, just unfasten the battery ground cable from the transmission then wrap a piece of tape around its terminal so it doesn't contact metal.


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1995 K75T 68,000 miles
    

robmack

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What do you mean when you wrote "... I then ordered a replacement wiring harness as once again ... I then spliced the wiring back together ..."?  Are you saying that you ordered a complete wiring harness from some place, received it and then proceeded to completely swap the old harness for the new one?  Or are you saying you actually tried to splice and solder together parts from one harness onto the old one?  I'm not clear.

Mind you, having the alternator light come on when you connect the battery is not a good sign.



Last edited by robmack on Thu Jun 14, 2018 10:40 pm; edited 1 time in total


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1987 K75 @k75retro.blogspot.ca
2011 Moto Guzzi V7 Racer
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Point-Seven-five

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Does your  bike have an aftermarket speedometer/instrument cluster?  If you have the original instruments, does the green neutral light come on?  Does the gear indicator show a zero?

Does the starter spin when you push the start button?

Are all the fuses good?  You might want to replace them even if they look okay.  They are known to go bad with age.

Does the headlight go out when you press the start button?

Are all te ground connections nice and clean and tight?

How are the starter brushes.  Worn brushes and carbon dust will wreak havoc with the electrical system.


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1994 K75RT
1994 K75S
1992 K100RS

Past:
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Laitch

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Least but probably not last, my used K-bike stalled on my first ride the day after I bought it. Turning the ignition to On and pushing the starter button did nothing, too. After scouting around the bike then reviewing the Rider's Manual, I checked the plug to the electronic fuel injection control unit beneath the tool box under the seat. It was not firmly connected because its latch wasn't holding it tightly. I pushed the plug into position, improved the tension on its latch then away we went—10 minutes riding time lost.

That's the only significant trouble I've had with the bike except riding it so often keeps me from accomplishing much. Smile


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1995 K75T 68,000 miles
    

kioolt

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When you hooked up the battery backwards you may have completely screwed yourself.  Electronics don't like to be hooked up backwards.  That plus side wire that you burnt didn't burn because it cares about polarity.  It was just the path for whatever was drawing such excessive current  As far as your starter problem, get a voltmeter and check your starter relay with it.  You should have 12 volts across the two small wires on it. By across I mean put one probe on one small terminal and the other probe on the other small terminal and turn the key on and press the start button.  If you don't have 12 volts at this point you need to determine if its the plus side or the negative side that is not working.  To do that put the plus probe on either small wire and the minus probe on a good ground.  Turn the key on and press the start button.  If you have 12 volts at this point then your problem is coming from your ignition control unit.  It controls the negative side small wire.


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2004 R1150RT 186,800 miles 
1991 K100LT 128,700 miles
1982 R100RT 106,900 miles
Total 422,400 BMW miles

AMA,BMWRA,BMWMOA


The cheapest thing on a BMW is the nut that connects the handlebars to the seat.
    

elementalfire

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Alright, answers to the multiple questions.

1) I remove the melted portions of the wiring harness between the starter relay and the battery connection and the alternator. The I butt spliced the wires with appropriate sized butt connectors and shrink wrapped them.

2) The battery light and clock turn on as soon as the battery is connected. I have checked for parasitic bleed off from the amperage and I do not see any noticeable drop.

3) The instrument cluster is OEM and from all indications is original to the bike. The neutral light, choke light and all other indicators turn on when the ignition is turned on. The headlight does not fade when I press the starter button. I have disassembled, cleaned and reassembled the starter switch assembly. It was slightly dirty but was making contact easily.

4) I have checked the voltage across the starter relay and it displays 12 volts without the key in the ignition.

5) There is absolutely no kick from the starter when the starter button is depressed.

6) All fuses appear to be in good order, I have removed, checked a reinserted all the fuses.

7) If the ground wire isn't making contact with the transmission do I not run the risk of making the entire bike a shock hazard?

Cool I am unaware of the status of the starter brushes but I do know that if I jump start from the battery directly to the starter it does turn over easily but no kick.

9) I removed the ignition coil cover to look at the coils and wires and everything seems to be in good order and connected well.

10) The ground connection at the transmission feels tight and shows no sign of corrosion or breaks in the wiring or sheathing.

Should I be looking at replacing the ignition control module under the seat?

Thanks to everyone,

elementalfire

    

charlie99

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possibly what you need to do  is measure the + terminal at the starter , ignition on , and start button pressed

if the voltage is lower than perhaps 10 volts at that time  you may have an issue of the starter relay

but you do need a very good earth wire from the battery to the gearbox lug - bolt , if that wire is lossy (incapable of carrying the amps required for a start )  a lot of things wont be working correctly during start conditions

btw the head lamps should switch off during start conditions (this is the power shed relay that does that )

you mentioned that the battery lamp illuminates as power is connected to the battery ?

that shouldn't happen until ignition is turned on

perhaps there is still some issues in the loom that you have repaired ?

just trying to offer some help at least

good luck


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MartinW

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@Point-Seven-five wrote:
Does the starter spin when you push the start button?

Does the headlight go out when you press the start button?

Are all te ground connections nice and clean and tight?

How are the starter brushes.  Worn brushes and carbon dust will wreak havoc with the electrical system.
If the starter is spinning but not engaging, suspect sprag clutch.  Not sure what is applicable to an 85 K  does it have a side stand switch? Have you tried pulling the clutch in?
Regards Martin.


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Laitch

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@elementalfire wrote:2) The battery light and clock turn on as soon as the battery is connected. I have checked for parasitic bleed off from the amperage and I do not see any noticeable drop.

3) The instrument cluster is OEM and from all indications is original to the bike. The . . . choke light turn on. . . when the ignition is turned on . . .

Should I be looking at replacing the ignition control module under the seat?
The clock should turn on when the battery is connected but as Charlie has indicated the alternator warning light should not be lit. Just having the clock on is enough to drain a battery after a while.

The choke light should not turn on unless the choke has been moved from its Off position to one of its two other positions.

You shouldn't be looking at the ignition control unit yet.

As Martin has observed, by your description the Sprag clutch component of your starter seems like it isn't working correctly. There are methods that might get it to work without major disassembly, especially if you can get your bike running by bump-starting it.


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1995 K75T 68,000 miles
    

RicK G

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Seems to me tha starter relay is shagged. Put the meter across the t main terminals of the relay and you should see 12 volts then press the start button if the volts drops to zero the relay is operating if 12 volts remain the relay is not operating. It explains why the headlight does not turn off and that the starter turns the engine when 12 volts is directly applied.


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caveman

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It sounds like you are not getting the ground for the load she'd relay (from starter) so not even getting power to the starter relay to energize starter.

    

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