Forum

[Hugh]

It seems that alternator has given up charging my battery as I get no reading across the battery when I rev bike. it used to rise to about 14v but now remains at 12.6ish. how easy is it to change the stator or to test it. I have uprated the bike to 12v. It has a new rectifier/control box in the electrical system. The magnito starts the bike and I don't use it at night but thinking about electronic ignition inside the magnito rather than a rewind as its 60 years old and as I know from my Bonneville such a system demands a fully charged battery. Hugh

[PeteF]

Disconnect the leads and see what voltage is coming straight off the alternator.
If that's OK then work your way up to find the problem. Most electrical problems are just loose wires.

[Adrian]

The alternator stator has just has three nuts holding it onto the mounting studs, easy enough to swap over, though if you still have the original rotor as well , that could have lost some magnetism.

If yours has the earlier type of alternator you'll have to replace the whole unit if the old one's duff, earlier rotors were smaller O/D, you'll probably also need an adapter ring to mount a new stator. Other option is to use a more recent Indian Bullet inner primary cover, the RM21 Lucas and Sparx 005 stators fit straight on, as will your original Redditch outer cover.

I'd be suggest that you DON'T to eviscerate the magneto if it's still working, and keep the ignition independent of the other electrics. The Lucas SR1 magneto was one of their better bits of kit, but there are plenty out there if you want to get a spare, either a good sparker, or non-runner which you can buy (cheap) and get rebuilt ready.

A.

[Jools G]

First off, as already suggested, is measure the output from the alternator itself. Disconnect it from the loom and measure the voltage output across the wires, bearing in mind that it's AC voltage at this point. The voltage should rise and fall with engine rpm. By the way, ensure that the engine is hot when you conduct this test as it's possible that it will work when cold but break down with heat (it's happened to me).

If the alternator is working ok, connect it back up and disconnect the regulator/rectifier outputs from the loom and measure the voltage coming out of this device. The voltage is now DC having been rectified, so don't forget to reset your voltmeter. If that's working ok, then it's a wiring problem from there on to the battery/ground.

[Adrian]

A much cheaper fix, if that's the case!

A.

[John-M]

A second vote for keeping the SR1 magneto, they are bullet-proof.
I have one on my trials Bullet and it has been totally reliable, (if you discount one occasion when I submerged it in a river.)
They have good spares availability, parts are easy to replace and it is easier to have a separate ignition system if you need fault find.

[Chris Tindal]

Mine suddenly stopped charging. On close inspection I found a broken wire on the stator. Quick solder and it’s been fine for two years.

[Hugh]

Thanks All. Will keep magnito and test wiring later for stator. Everyone helpful as usual. magnito seems to stop working when hot. Changed condenser and points so maybe a rewiring etc. certainly with electronic would need a fully charged battery a new coil and output from alternator. Cheers all on a very stormy day in wales. Hugh

[Jools G]

If the magneto stops working when it's hot, then the shellac coating of the motor windings is past its sell-by date and the mag needs re-winding (running when cold & failing when hot are the classic symptom). The shellac melts as it gets hot and the windings then short out, leading to your loss of sparks.

I fear a re-wind won't be cheap, but the SR1 does generally have a very good reputation. Failure with old age is common to most things (including us!).