Engine dies

[Queenslander]

G'Day
I have just purchased a 1958 G3 LS and am having some electrical problems.
New batter fitted and the alternator has supposedly been replaced.
Bike starts and running with lights on for around 5 minutes, the the motor cuts out.

After checking fuel etc., I switched off the lights and the bike started first time.
But turning lights on an it cut out.
After a few checks that this is happening, I rode bike home without lights operating and all went well.
Once home I put a multi meter on the battery and got 6.2V and good amps.

The Amp meter gauge on the light housing twitches a bit but hardly moves off zero when running and I would not trust that gauge anyway.
I have heard that the magnets in the alternator can become discharged which will stop charging the battery and need re-activating.

Any ideas?
jon

[Trefor]

Try putting a voltmeter on the battery while the bike is running and see if the voltage is maintained when you turn on the lights and rev up the motor. If not, the alternator is not charging enough. I have a 1962 Triumph 350 with alternator and coil ignition, a similar electrical system. The original Lucas system (unless a previous owner has modified it) has a very low output alternator and the charging circuit is unregulated and relies on the position of the light switch (load on the battery) to regulate the charge into the battery. I recommend you fit an electronic regulator and a Led headlamp and taillight. I did so years ago and have no problems with the electrical system.

[Queenslander]

Come to think when I bought the bike; the seller said something about fitting some newer regulator or something.
I will check the charge rate as suggested.
On another point but possibly associated, the key ignition has two settings and the former owner said switching it one way or the other impacted on the charge rate, but he could not remember which way was for low and which for high.
Again a dodgy Lucas switch.
Can you suggest which way is which?

[Queenslander]

Also Trefor, is your bike 6V and if so where did you get the 6V LEDs from in Aus?

[AndrewM]

Good source for solid state regulators and suitable LED bulbs for old British bikes is www.dynamoregulatorconversions.com in the UK

[Queenslander]

Thanks Andrew. Pitty there's nowhere closer.

[SPRIDDLER]

On another point but possibly associated, the key ignition has two settings and the former owner said switching it one way or the other impacted on the charge rate, but he could not remember which way was for low and which for high.

Can you suggest which way is which?

Unless the PO has modified the wiring, the alternator output is increased automatically when the lights are turned on. The switch functions (including the use of the brief period only 'Emergency start' position) are explained on pages 73 and 74 in the Owners Manual and the wiring diagram is on pge 85.
Link here:

http://archives.jampot.dk/book/Owners_m ... Models.pdf

[Groily]

I think it would be good to establish what the PO actually did before getting too far in.

If the alternator was 'replaced', was it replaced with a 3 wire one, or with a 2 wire one do you know? If the latter, then the PO may have fitted a combined 6v regulator and rectifier such as the A Reg 6. These changes have an effect on the basic wiring. You can see how many alternator wires come out of the rear of the primary chaincase with any luck . . .

If the alternator remains a 3 wire one, then the PO will have retained the original switch wiring and a simple rectifier probably - with EM for emergency ignition one way, and normal running the other.
In the EM position (usually marked on the switch with EM to the left, normal ign to the right) the alternator supplies current - AC - directly to the switch and thence to the coil, just for starting when the battery is flat.
Once it's running you swap over to the normal running position or things will start to misfire or the engine might even stutter to a stop.
In the 'normal' position, the alternator delivers DC current via the rectifier to the battery and to support whatever is on, with the wire that supplied the EM IGN feed also being diverted through the rectifier.
The charge rate is increased, or should be, when the lights are switched on. With them off, not all the alternator coils are active. There are 3 pairs, and all three are only active when everything is switched on. This 'coils in and out' function is controlled by the lighting part of the PRS8 type switch.

It would be good to compare what you have with the diagram on p85 in the link supplied by Spriddler.

If what you have doesn't look like that, then you might find something useful in this other thread where there are good diagrams for single and two-switch arrangements (I presume you have the single combined one) using 3 wire and 2 wire stators. The latter is a 12v system but the wiring - if your PO has used a combined 6v reg/rectifier - is equally applicable for the single switch set-up: https: //forum.jampot.com/viewtopic.php?t=29388

It's not that likely that the permanent magnet rotor has given up on you, but it's not impossible. Normally, one would replace it with the stator if replacing the alternator, but it's certainly not a given. Early non-welded rotors can be a bit fickle I believe. Assuming the alternator does actually work, it is more probable, I think, that there is a wiring error causing the lack of charge, lack of activity at the ammeter, etc, which will be revealed if you go through things methodically to see what you have, and then ensure everything is hooked up to suit what you find.

With the engine running at moderate rpm, you'd want to be seeing 7v across the battery and maintained when things like lights are switched on. Fully charged, a good 6v battery should show 6.6v.

[Queenslander]

Thank you guys for the information and the link to diagrams/manuals.
I'm working over the next couple of days and will be studying up before attacking the problem on Thursday.
I do have that 3 way ignition switch on the headlight casing but cannot see any markings so hopefully the diagrams will set me right on this.
Then I'll be giving the multi-meter a workout.
Hopefully I will be able to report a successful outcome by late this week.
Jon