Farmall A H4 Magneto problem

winds1sj · Nov 19, 2008

I have a 1941 Farmall A with the H4 mageneto on it and I am getting no spark. I replaced the rotor, cap, and wires. I took it off and when the points are sepearted it is grounded as well as when the points are connected. The coil shows 10.2K ohms between the primary and secondary wires. Any help would be appreciated.

winds1sj

Anonymous-0 · Nov 19, 2008

howdee.
how bout the impluse spring? sometimes they get weak or broken. or the pawl springs. happens to them also.
when turning the mag coupling, there should be a good bit of resistance before the impluse trips.

good luck with it.

J in Pa

ScottyHOMeY · Nov 19, 2008

Am I reading correctly that the points are grounding whether they are open or closed?

winds1sj · Nov 19, 2008

yes, it seems that the primary wire and the ground are connected because there is no resistance, I guess the primary wire would be grounded. Is the coil bad or is it something else. I had some voltage coming out of the secondary but it was really high and fluxuated all over the place. Is there supposed to be a constant voltage.

winds1sj

ScottyHOMeY · Nov 19, 2008

The springy side of your points shouldn't stay grounded when the points are open. Could be a bad coil. Could also be a short in the mount of your points. You didn't mention replacing them or the condenser.

Another couple possibilities come to mind quickly.

1) The primary wire between the coil and the points is shorting to the maf body. It runs through a narrow channel and chafed or broken insulation could cause it to short. Check its condition.

2) Either one of the two (inside and outside) insulators around the ground stud of the condenser could be broken with age or from having been tightened down too hard. Look them over as well.

Either one could cause your poins to be grounding when they shouldn't.

Just to add a third idea to go with the same thought, check out the condition of the insulator that the spring side of your points mounts to.

winds1sj · Nov 19, 2008

Took the coil off and everything checks out as it is supposed to. So i took the coil off and checked the primary wire to the ground and found it was grounded. so i think it is the coil. The condensor looks new and seems not to be grounding out. So i am guessing i need a new coil.

El Toro · Nov 19, 2008

Clean the points with some 320 wet or dry before buying a coil. Check the magnets for magnetism using a screwdriver. It should attract that with a lot of effort. Make sure the point gap is .013". Hal

Bob · Nov 19, 2008

Even with the the points "open", the primary coil winding is connected between the movable (insulated) point and ground.

I can't remember the coil primary resistance "spec" offhand, but it is quite low, and will seem like a "short" unless checked with a low-Ohms setting an an Ohmmeter, even if the coil is good.

Bob · Nov 20, 2008

How many Ohms from the primary wire to the ground tab?

winds1sj · Nov 20, 2008

Hi,

I replaced the coil with no change. So, I looked at the cap and rotor again and found that the new rotor was bent down just a little bit from the manufacturer. Bent it up a little and I have blue spark. Thanks for the help.

winds1sj

Farmall A H4 Magneto problem

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