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H4 Mag on Super A-V quit

C

ccaissie

Member
Client was running '48 Super A-V and it quit. I checked for spark...nada
Noted that I wasn't getting the usual magneto impulse coupling click, so pulled it off and disassembled on bench, and find the pawl springs pretty weak.

But I read that these springs were later added, and the pawl mechanism/ impulse coupling is only for low cranking rpm's, so weak pawl springs was not the cause of the stall.

Yes?

So, really I need to check other factors in the magneto, like coil resistance etc.

Yes?

Anything else I can check out while it's on the bench? The pawls are really floppy, and springs are weak. Tractor ran pretty well, with an occasional miss and stutter that wouldn't respond to carburetor adjustments.

Oh yeah, client had carb off when it wouldn't start one day, and now it takes a whiff of ether to start...choking it will flood it. Float too high or too low? Plugs show tan insulator/black nose, but likely from oil burning.

C
 
Usualy when a mag dies its because of the coil when it cools down it will have spark again till it warms up. It was recomended that the mag be removed once a yr and the impulse area to be washed with kerosene. A weak impulse will still fire enough to start.
 
Touch the magnets with a flat blade screw driver to check for magnetism. They may be getting weak. Hal
 
The magnet in an H4 seldom if ever needs recharging. A condenser can go weak when it gets warm just like the coil.
 
do the easy thing first. check the points. Clean them and re-gap them. If still no spark, you can go deeper, like condenser and/or coil.............

Also, are you wires copper core or composite. Mag's do NOT like composite wires.................copper only.
 
One of the pawl springs broke while assembling it..obviously was worn and weak.

Even if that was not the problem, gotta replace it.....

Local IH dealer can't source it new. From TC-39, it's part # 51303 D.

So, I've checked condenser and points...ok. Condenser shows increasing resistance when testing....after discharge, it shows the same rise, so i assume it's not shorted or open. Was new a couple years ago.

Magnet seems strong, all else looks good

How do I check the coil & windings? Primary? Secondary? I'll search other posts, but could use a quick reply on this.

Thanks,
C
 
Coil test instructions seem to leave out a couple of clues.....

There's a solid iron core that is obviously zero resistance.

There's a metal clip that looks like it's coming out from the iron core, but shows no continuity with the iron core.

The metal clip shows .5ohms to the wire exiting the coil, but nowhere else.

Every other combination shows open circuit/ no continuity.

With descriptions like "12k" or "6200ohms on the secondary", I'd expect to find something like that somewhere on the coil, but i believe
i've got a bad coil.

Thanks,C
 
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