Magneto Distributor Cap

[LeoM]

I have a Magneto that came off a Cub that I cannot fit the distributor cap back on. The cap was not installed when I got it. With the rotor installed there is a gap of .25" - .5" between the bottom of the cap and the top of the distributor housing. I tried a different installed on another Magneto Cub and the problem is the same. I cannot find the number J 4 on the Magneto. There is a serial number H 4983289, a number cast on the housing under the rotor 6483DX and a patent number 2,232,508.
Are there different style caps or different versions of the J - 4 Magneto, or am I just missing something obvious ?

[Don McCombs]

Can you post a photo of the mag?

[Eugene]

Photo of the magneto interior and exterior, and any markings on the magneto. It's possible that it's not a J-4 magneto or a magneto for an IH manufactured tractor.

I would have to do some research as to the time frame, but some time back the tractor and magneto manufacturers went to a standard magneto mounting base.

[Jim Becker]

That is an H-4 magneto, used on other letter series Farmalls. It uses different tune-up parts than the J-4. The H-4 magneto is not a good fit on a Cub. The physical size makes it difficult to install and the lag angle is way off for a Cub.

[LeoM]

I believe Jim is right. It is marked as a IHC Magneto and when I was turning the drive end hub I noticed that the angle of the rotor was way different than what I thought it should be. I'll post some pictures as soon as I figure out how to.

[LeoM]

[LeoM]

Sorry for the poor quality. If needed I can retake.

[Glen]

Hi,
I think in your pic it shows H 4 at the beginning of the number stamped in the magneto.
Like Jim said, they were used on several other models of IH tractors.
They do use a different distributor cap than a Cub.
If you are using it on a Cub, it would be better to buy a J 4 magneto, or a Battery Ignition Unit for it.
Here is a pic of a H 4 on a tractor.

[Jim Becker]

. . .
I think in your pic it shows H 4 at the beginning of the number stamped in the magneto. . . .

Yeah, the clue was in Leo's first post.

There is a serial number H 4983289,

The H4 prefix identifies the model. The serial number 983289 says it was made in November 1947.

You would definitely be better off with a J-4 mag or a battery ignition unit (from a Cub to get the right advance curve).

[LeoM]

Thanks to all.

"Wrenching with Rachel" has a very good video of rebuilding a Letter Series magneto. I will attempt my first rebuild on this 1.

I have an A and 2 Super A's that are in line to rebuild. The 1 Super A was a father and son project that got interrupted when the son discovered girls. The engine is disassembled. I am planning to take it to the Deep South Cub Fest next Feb. to get help putting it back together. If this Magneto fits I may use it on that tractor.

[Jim Becker]

I have not watched that video. However, Rachel has been known to miss a detail or two. So I suggest watching the video then reading the applicable section of the right service manual.