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Old 19-10-07, 09:07 AM   #1
jemglen
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Default Reviving a non-working magneto

Here's a tip I picked up recently which has brought my M-L MCK1 magneto (1928 Lister A) back from the dead and saved me a hundred quid or so on a refurb.

If, when turning your mag by hand through the 'dead spot' there is no spark (holding the HT lead just a fraction away from the body of the mag as you turn the sprocket) it could be that the armature is dead. Before consigning it to the scrap bin though try this: attach a socket suitable for the nut that holds the sprocket to its spindle to your electric drill (I used the extension bar from a power screwdriver set and a step-up drive adaptor from a socket set). Mount the mag in your vice, attach the drill via the socket to the spindle nut and run it in REVERSE against its normal orientation (ie if, like mine, the mag is an anticlockwise device, spin it in a clockwise direction) at around 500rpm for a minute or two. Don't be over-zealous with time or speed, just a give it a quickish spin up at a reasonable speed.

Back on your bench try the mag again for a spark as outlined above. With a bit of luck, it will have magically (!) come back to life. It could be that you need to try the reverse spin a couple of times to get it to work. If it doesn't, and assuming you've cleaned and set the points and attended to any other routine maintenance, at least when paying for a rebuild you'll know you did all you could. Good luck!

Jerry
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Old 19-10-07, 10:39 AM   #2
buzzy bee
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Hi

Sounds like a good tip, something that we can all do too!

Cheers

Dave
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Old 19-10-07, 01:14 PM   #3
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I thought my motorcycle K2F magneto had died, it turned out to be the ground brush wasn't making contact with the slip ring. I'm not sure if the stationary engine magnetos have these but it too is something to check before considering a full rebuild.
hth Dave.
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Old 19-10-07, 03:22 PM   #4
Paul_Sterling
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hi dave, i have probelms with the magneto on my A1's the ones fitted with a Wico series A seem okay, only i havent fitted the magnetos on them yet (im a coward when it comes to electricity!) but the other one is a completely cast aluminium one, (i think its a wico but not sure) it sparks, albeit poorly and doesnt have an impulse, any ideas on that?

Paul.
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Old 19-10-07, 03:40 PM   #5
djrm
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Quote:
Originally Posted by Sterling_the_legend View Post
it sparks, albeit poorly and doesnt have an impulse, any ideas on that?
Paul.
What is an impulse?

The usual suspects on a poor magneto are the points, the armature, the magnet, and the condenser. The points need to be adjusted for the correct gap, perhaps 12 thou. The armature may have poor insulation or worse, shorted turns, and the condenser may be either leaky or completely open circuit.

On a typical motorcycle (K2F) magneto the condenser is on the end of the armature and quite tricky to replace I believe.

I have heard that it may be possible to fit an external condenser across the points if the old one is open circuit but I'm skeptical whether that would really work.

Sorry but I have had very little experience of the stationary engine kind since about 30 years ago on my old 600cc JAP engined Howard rotavator which had something similar, possibly a Wico.

Dave.

Last edited by djrm; 19-10-07 at 04:06 PM.
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Old 19-10-07, 04:19 PM   #6
Paul_Sterling
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cheers for you help anyway dave

Paul.
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Old 19-10-07, 04:57 PM   #7
djrm
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But what is an impulse Paul?
I see that the internal file website has some magneto manuals available to download.
hth Dave.
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Old 19-10-07, 11:14 PM   #8
gardnerman
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Quote:
Originally Posted by djrm View Post
But what is an impulse Paul?
I see that the internal file website has some magneto manuals available to download.
hth Dave.

Basically as in the case of the WICO A, a spring is fitted to hold back the travel of the armature until a set point then it flicks the mag sharply, giving the point of rotation at the time of spark a higher speed at start up so that it gets the sort of speed you'd get when the engine is revving.
I hope this is clear.
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Old 20-10-07, 04:32 PM   #9
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You can hear the impulse mechanism as an audible metallic click when spinning over an A1 on the handle.

Jerry
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Old 22-10-07, 10:15 AM   #10
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Hi,

I always prefer to have a magneto professionally repaired. Yes, there are 'methods' of getting old magnetos to spark but these in my experience are only temporary measures and at some stage the magneto will fail. After all, an engine is only as reliable as its magneto and if itís been around 50+ years it could be forgiven for being dodgy.

Cheers

Andrew
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