test for points spark on magneto ignition

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test for points spark on magneto ignition

Postby Joe in Pa. » Sun Nov 22, 2009 9:02 am

I've been helping out with a rebuild of a "48" and after changing out the points-condenser, we have no spark at the points.
Reading back through the posts I still have a question or 2:
On a Magneto type ignition, can you check for spark at the points?
I have done mine {coil-type} and can see the spark when turning the motor over with the key on, but am unable to on this particular tractor, anything I might be missing, I'm kinda stumped? Thanks in advance,Joe
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Re: test for points spark on magneto ignition

Postby Bigdog » Sun Nov 22, 2009 10:23 am

The magneto must be turning for a spark to be generated.
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Re: test for points spark on magneto ignition

Postby Eugene » Sun Nov 22, 2009 10:42 am

I bench test magnetos. Gently install the magneto in a bench vise. Drive the magneto with a variable speed electric drill and socket. Make sure the coil wire has a spark plug and the spark plug grounded to the vise/magneto.

To add to BigDog's comment. The magneto rotor (magnets - not the distributor rotor) has to be moving at some speed to induce/create the electricity in the coil. Normally the snap of the impulse coupling is sufficient to create the electricity/spark.
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Re: test for points spark on magneto ignition

Postby Jim Becker » Sun Nov 22, 2009 11:28 am

Eugene wrote:The magneto rotor (magnets - not the distributor rotor) . . .

"Armature"
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Re: test for points spark on magneto ignition

Postby Eugene » Sun Nov 22, 2009 11:37 am

Jim Becker wrote:
Eugene wrote:The magneto rotor (magnets - not the distributor rotor) . . .
"Armature"
Yup armature. I used the term magneto rotor which is used on one of my reference books. The book also use the term distributor rotor.
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Re: test for points spark on magneto ignition

Postby Jim Becker » Sun Nov 22, 2009 12:20 pm

I probably should have left this topic alone! This post was probably best left unwritten and surely should be left unread.

This terminology gets confusing, especially when MEs and EEs don't even use the same ones. On things that rotate, generaly an "armature" has to carry electricity. The rotating part in the Cub magneto is a magnet with no windings. Thus it is a rotor, not an armature. The IH Parts Catalog uses that terminalogy, exactly as you did in your first post.

A lot of the older style magnetos have a big horseshoe magnet around the outside, with the rotating part between the magnet poles. In that style, the rotating part has windings that produce electricity and really is an armature. With the confusion factor of the "distributor rotor" also built into most magnetos, I usually just stick with "armature" for the rotating part of any magneto.

If you look at the parts breakdowns of generators and starters, the rotating part is called an armature. The rotating part of an alternator is called a rotor. Even though an alternator rotor carries some electricity, it produces the magnetic field. The output electricity flows from the stator. The stator could arguably be called an armature, but by convention in AC equipment the stationary part is conventionally called a stator. IH and Delco (and as far as I know everyone else making those units) use the same terminology.

That should have confused things enough!
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Re: test for points spark on magneto ignition

Postby Boss Hog » Sun Nov 22, 2009 12:47 pm

When the mag is qpperating as it should, you can turn the mag be it by hand or on the tractor, and when it trips there will be a bright blue spark at the coil wire. The wire should be held close to the mag itself, about 1/4 to 1/2 inch.The trip I am referring to is the impulse. If the impulse is not working. It will not crank as it should. If turning by hand you can feel the spring winding up till it trips. I hope this helps. There is no fire at the points like on a dist. The spark is generated by the mag. itself while turning. I hope I have not confused an already confusing topic.
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Re: test for points spark on magneto ignition

Postby Boss Hog » Sun Nov 22, 2009 12:49 pm

I should add, I know just enough about mag.s to be dangerous
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