The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: Stephen Foster on 19.10. 2022 19:16
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Ive got the 1954 plunger A10 running perfectly now but can get the magneto to cut out ?
Ive tried 3 magneto end caps ,remade the cable ...tested it with and without the cutout button on the handlebars ..shorting the cable against handlebars ,engine studs , etc .
The Earth brush is in place and fine .
The points bolt is fine and contacts the magneto end cap carbon brush .
Ive run out of ideas now ?
Thanks for any suggestions ?
Steve ..
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G'day Steve.
I'd revisit the earth brush. Clean where it contacts the armature and inside it's keeper. Is it and the spring long enough?
One of the sparky's will be along soon.
Cheers
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Can't get it to cut out? Normally it's the other way round ...... *smile*
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G'day RD.
Yes not often we would complain aout that
I had the same problem with mine the first time I started the 51 A7. No internet back then. I made a new brush out of the carbon center of a size C battery!
cheers
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I agree with Musky's thought ref the earth brush. It's the most likely area for reasons he suggests.
To check, a meter from mag spindle to mag body should show very low resistance, close to zero ideally, if the earth is doing its job. (Have to allow for a degree of error at low readings on many meters though.) If you see an obviously high reading there, t'ain't right and could be the problem.
Let's assume, though, that there is perfect continuity between it and the armature inside . . .
Have you tried holding a bare wire (pre-attached to an earth) against the (clean) head of the cb centre screw while the engine is running? Ie bypassing the cut-out arrangement and button completely?
That ought to stop it. If it does, fault is in the cut-out arrangement - however unlikely as you've revisited it several times.
Some basic info if you want to confirm health at the cb end . . .
A meter from centre screw to mag body, points open - about 0.5 ohm.
With the points shut - 0 ohm.
(0.5-0.6 ohm is the approx resistance of the low tension winding.)
From the cut-out wire itself to any earth you'll probably see a few ohms - that's the brush and spring. But it shouldn't be a high number.
If readings are all good and the engine still won't stop using a direct wire off the centre screw, then we're in very weird territory.
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Thank You all for the suggestions .
Unfortunately I have tried them all now ..Earth brush fine ,3 different mag end caps ,new cable.
Cable offered onto the points stud and shorted onto barrels ,crankcase ,horn bolt ,etc .
No different ..Im baffled now ..the bike starts and runs perfectly just wont stop !
No idea where to look next ?
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Hi , mine was exactly the same today and it was the wire from the cut out switch , Where it go,s in to the endcap it had been soldered on to a little brass disd and the face was manky and wire hanging on by only 1 strand when i looked closely . remade connection and it works fine .
Cheers dave
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Thank You all for the suggestions .
Unfortunately I have tried them all now ..Earth brush fine ,3 different mag end caps ,new cable.
Cable offered onto the points stud and shorted onto barrels ,crankcase ,horn bolt ,etc .
No different ..Im baffled now ..the bike starts and runs perfectly just wont stop !
No idea where to look next ?
Do you have a spare set of points? If you have, try changing from brass type to steel type or vice versa.
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Thank You for the helpfull replies .
I do not have steel points as the ones fitted are brass ?