H4 Magneto Rebuilt But No Spark to Distributor Cap

Farmall Super A, AV, 100, 130, & 140 1939 - 1973
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southern-jim
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Zip Code: 65704
Tractors Owned: Farmall A
Location: Missouri

H4 Magneto Rebuilt But No Spark to Distributor Cap

Postby southern-jim » Sat Jul 30, 2022 3:20 pm

Hi Everyone,

I hope someone out there can offer some advice to my problem here.

I've rebuilt my H4 magneto for my Farmall A with all new parts.

I get a solid spark from the coil cover, through its wire to the spark plug tester.

I do not get a spark to to any of the four plug wires.

I've tested the new plug wires by hooking each of them up to the coil cover and they are all good.

The distributor cap is new and i also tried putting the old cap back on as well. Still no spark.

I've tried 2 new rotor caps and even tried the old cap. Still no spark.

The rotor cap points at the wires once the impulse snaps.

Would anyone know what is going here?

Thanks very much!

Jim Becker
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Re: H4 Magneto Rebuilt But No Spark to Distributor Cap

Postby Jim Becker » Sat Jul 30, 2022 3:43 pm

I'd start by opening up the little gear case that drives the rotor and make sure the gears are in time. Use the "R" mark for a right-hand rotation magneto.

southern-jim
Posts: 7
Joined: Tue Apr 12, 2022 11:22 pm
Zip Code: 65704
Tractors Owned: Farmall A
Location: Missouri

Re: H4 Magneto Rebuilt But No Spark to Distributor Cap

Postby southern-jim » Mon Aug 01, 2022 7:19 am

Thanks Jim. I'll pull the cover off and check that out. Come to think of it I had set the marks on this the other week and that had fixed the problem. Now the problem is back. Perhaps the gear is worn and it is skipping over some teeth? I'll try resetting and seeing if the problem comes back.

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Stanton
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Re: H4 Magneto Rebuilt But No Spark to Distributor Cap

Postby Stanton » Mon Aug 01, 2022 9:28 am

Parts Manual has the Distributor Gear #49420 DX (24 teeth) and the Rotor Pinion #47417 DX. Check to see if the teeth on both those items are intact and not skipping, damaged, or worn.
Stanton
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