mag cap for Farmall A

Bryan Monaco · Oct 21, 2008

I have a 1947 Farmall A. I was looking to replace the magneto cap. My old one is rather nasty. According to my manual the tractor has a H-4. I bought a cap for an H-4 and it didn"t fit all that good. I put it on and it ran like crap. I put the old cap back on and it ran fine. The old cap and the H-4 cap I bought are different. The original cap isn"t as tall. The local parts store shows only the H-4 cap in their book so I am at a loss of what I really need.

What cap should I buy?

Andy Motteberg · Oct 21, 2008

YT has the cap for the H-4 magneto.

Bryan Monaco · Oct 21, 2008

I already bought an H-4 cap, but it didn't fit. Is there another magneto besides the H-4 for an A.

Andy Motteberg · Oct 21, 2008

You can still buy a new H-4 cap that fits. The place you got your cap gave you the wrong one.

Bryan Monaco · Oct 21, 2008

I ordered a cap from a parts store in town and I will get that in the morning and compare it to the "H-4" cap I bought, that doesn't fit, at Rural King.

John M · Oct 22, 2008

Sounds like you got the cap for a distributor, or you have a distibutor and got a mag cap.

rustyfarmall · Oct 22, 2008

First, are you sure you have an H4 magneto, or has it been changed over to a battery ignition distributor?

Bryan Monaco · Oct 22, 2008

It is a magneto for sure. If it is an H-4 I don't know for sure. The package for the cap I bought says IH H-4 magneto cap.

D.redgreen · Oct 22, 2008

A distributor and a j4 cap while resting on the table will have all five wire plug holes essentialy the same height. On the H4 the center one will stand noticably higher than the four around it. None of the three caps are interchangable.

Bryan Monaco · Oct 22, 2008

I just got back from the parts store and the cap they had for the H-4 is the same as what I already had. We looked over the cap that was on the tractor and compared it to the photos in the book. It looks like my A has a J-4 magneto. According to the manual the A didn't use the J-4, but I guess somebody stuck on on somewhere along the line. The H-4 cap is too tall and the notch doesn't line up correctly.

ScottyHOMeY · Oct 22, 2008

I suppose it's possible that you have another make of mag on there. I've got a tractor book here with a picture of a beautifully painted C on the that has a mag that on it that is very obviously NOT an H4. Wico, FM?? Can't tell an don't know enough to guess. Point is that the H4 would have been factory but it appears that there are others tha will fit/work.

An H4 is pretty easy to identify. It'll have a rectangular bakelite or plastic cover on the top, with the secondary wire running to the cap coming out the rear side of it. The distributor cap is the conventional round configuration. On the body, below the coil cover, it will read a all about being made by IH . . . At the bottom of all that, on a narrow machined flat spot will be a serial number that begins with H4.

If what you've got is nothing like that or enough different, I'm wondering if it might be one of the mags that fit on the F12s or F14s. Try hailing magman on here in a separate post. He'd likely know for sure what the options are for other mags that would fit and help you identify what you have.

ScottyHOMeY · Oct 22, 2008

MagMan is farmallmagneto.com, though his site says he works mostly with H4s and J4s (Cub)

Another is mainelymagnetos.com. He's up in northern Maine and seems to work with older and other makes of magnetos. Might be worth a try, as well.

mag cap for Farmall A

Bryan Monaco

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Andy Motteberg

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Bryan Monaco

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Andy Motteberg

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Bryan Monaco

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John M

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rustyfarmall

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ScottyHOMeY

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