Electrical head scratching

SeanW · Sep 28, 2020

Wonder if someone who understands electric stuff better than me (almost anyone then) can maybe point me towards things to test / likely culprits on my 79 R80/7 which has been doing some odd things for some time now.

The main symptom seems to be the battery going flat. I initially thought it was an old battery so replaced that but it's doing the same thing. Never goes completely flat (lights work etc) but there's not enough charge to turn the starter or even make relays go clickety click. So I can have had it on charge overnight, battery seems fine, engine cranks and starts, but at the end of a 50 mile trip the starter is just dead again. I can bump it OK and it fires up but then on the return trip last night having done that I was getting very brief occasional misfiring, just cutting out for a fraction of a second then carrying on ok. Seemed to be more frequent at higher revs, but that might be a red herring.

The other obvious thing to mention is the voltmeter shows 14.2 volts with the engine running above 3000rpm and lights off and 13.2 with lights on. So presumably the alternator is working ok (ish) - if that's the case how come the battery is just running down during use?

michaelmy · Sep 28, 2020

maybe the 1983 R 100 R thread by Packer, below will help?

Nin · Sep 28, 2020

Maybe worth looking at the brushes on the starter motor itself. That sounds like the problem.

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DrFarkoff · Sep 28, 2020

Do you have a Charge lamp showing on your dash? Is it going out ?? Its it lighting when you switch on the ignition

If not? Then the rotor is not getting its Exciter current! Also from memory its a 3 watt bulb not a 5 watt bulb for it

Have you been at the Diode board or starter recently before or during these symptoms ?

Check that the diode board to starter heavy red wire has not pulled off at the Diode board or the Starter pole
Basically the charge is not making it to the battery this way

And of course brushes if they are getting shorter or the Slip rings are dirty

squibb34 · Sep 28, 2020

No experience on the R80/7, but from other bikes I've had the pleasure of dealing with over the years, I'm thinking reg/rec, the stator starting to fail, or some dire corroded neg/earth connections.

Good luck finding the culprit.

Bubb · Sep 28, 2020

Try the simple stuff first:

Check your battery earth lead is tightly fastened at BOTH ends.

Then check red diode board wire. Then all other earths.

Good luck, wiring is my bete noir too! (abut I am learning...slowly)

SeanW · Sep 29, 2020

Thanks all, will give those things a go and report back

SeanW · Sep 29, 2020

charge lamp behaving as expected, not been messing with diode board or starter, brushes still have life....

so probably broken or corroded wire somewhere. I have had corroded and fractured wires at connectors to relays etc under tank before...

DrFarkoff · Sep 29, 2020

SeanW said:
Thanks all, will give those things a go and report back

BE careful checking the earth at the gearbox!!!! Do not over tighten it!!

If the main earths are bad on the battery or gearbox an Airhead with a Bosch starter will not turn over

SeanW · Oct 3, 2020

Bit of an update. First of all, the starter won’t spin at all now even with a recharged battery or jumped from a car battery. No relay clicking either.

Tested the main earth lead and that’s fine.

Ground to the frame under tank looks OK

Usual three lights come on with ignition on but start button does nothing.

I had a rummage with the relay wiring under the tank where I’ve had broken wires before and found that one of the green-blue wires to the starter relay had indeed fractured under the insulator where it joined to the connector. Great, I thought, that must be the issue. So I repaired the connection and connected everything back up again, hit the starter, and ... nothing still. :confused:

So a bit back to square one. Any ideas for what to check next?

Gelandestrasse · Oct 3, 2020

Sean, It seems there is more than one symptom. Number 1: no starting. Number 2: battery not charging/going flat even with good charging system. Perhaps there are more symptoms?

I love solving electrical problems on my airheads but I don't expect to do it quickly. Absorbing the circuit diagram with the symptoms of an evening and letting it send me to sleep, often a strategy pops in.

Before I look at your circuit diagram, I can have a reasonable stab at no 1. The clutch interlock switch may be inhibiting starting. That would present no starter relay clicking. So check its connections, wiring, switch operation with a meter. Second, the kill switch (if you have one) may also be playing up. A good spray with GT85 or similar and plenty of exercise should help.

ianboydsnr · Oct 3, 2020

SeanW said:
Bit of an update. First of all, the starter won’t spin at all now even with a recharged battery or jumped from a car battery. No relay clicking either.

Tested the main earth lead and that’s fine.

Ground to the frame under tank looks OK

Usual three lights come on with ignition on but start button does nothing.

I had a rummage with the relay wiring under the tank where I’ve had broken wires before and found that one of the green-blue wires to the starter relay had indeed fractured under the insulator where it joined to the connector. Great, I thought, that must be the issue. So I repaired the connection and connected everything back up again, hit the starter, and ... nothing still.

So a bit back to square one. Any ideas for what to check next?

Relay will be either positive fed or earth fed from the starter button, it’s more likely to be earth fed, in that the relay is powered from the ignition and the starter button provides the earth to engage the relay,

So try the relay with a direct earth, if it doesn’t work, make sure the relay has power connected, if it has both and it doesn’t click then it’s broken, if it then does work, the wires supplying the power or earth are broken somewhere

It’s easier to do such checks with one of these
https://www.ebay.co.uk/itm/Sealey-P...306455&hash=item2c9110306e:g:h-IAAOSwotJd5mlS

You connect it to the battery and one side of the switch gives power to the tip, the other side gives earth, but it’s circuit protected

SeanW · Oct 7, 2020

ianboydsnr said:
Relay will be either positive fed or earth fed from the starter button, it’s more likely to be earth fed, in that the relay is powered from the ignition and the starter button provides the earth to engage the relay,

So try the relay with a direct earth, if it doesn’t work, make sure the relay has power connected, if it has both and it doesn’t click then it’s broken, if it then does work, the wires supplying the power or earth are broken somewhere

It’s easier to do such checks with one of these
https://www.ebay.co.uk/itm/Sealey-P...306455&hash=item2c9110306e:g:h-IAAOSwotJd5mlS

You connect it to the battery and one side of the switch gives power to the tip, the other side gives earth, but it’s circuit protected

Thanks to Ian! I checked the continuity of the live and earth feeds to the relay using a test light, both were fine, so following your logic, ordered a new relay. Starter now works perfectly.

Now we will see whether I was just imagining the battery was going flat cos the starter wasn't working. Hopefully charging and battery will both be fine. Though relay problems wouldn't explain occasional cutting out / misfiring, so I may be back shortly if that's still happening. I bought a new solid state regulator at the same time as the relay as one of the terminals was close to breaking off; maybe that will fix things?

Electrical head scratching

SeanW

Registered user

michaelmy

Active member

Nin

Well-known member

DrFarkoff

Grumpy Ole Git!!!

squibb34

Well-known member

Bubb

Dogsbody

SeanW

Registered user

SeanW

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DrFarkoff

Grumpy Ole Git!!!

SeanW

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Gelandestrasse

Well-known member

ianboydsnr

Well-known member

SeanW

Registered user

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