Dist interchange

Can a battery ignition unit from an A be put on a M?

Yes (except MD)
It would be best to make sure the centrifugal advance springs and weights are the same, or the advance curve will be off some, But it will work. JimN

Jim, I failed to say that I want to replace a magneto with battery ignition. Would weights and springs transfer from a mag to battery type?
I an going to use a electronic type with 40,000 volt coil. Reading other posts I figure I could open SP gaps to .040...? Thanks

No common parts between mags and Dist. Look up the part numbers in caseih.com web site and see which part numbers are on the components.

I have been running battery ignition from Super M on my A for over 25 years and it runs fine. There is some difference in advance curves but you will never notice it if you set timing by ear as most do, after all magneto has no centrifical advance and some people swear by them.

As mentioned earlier, the advance is different but not much. The tractor magnetos had a 35° advance, the ag distributors have 40°. I doubt if you'll notice much difference at rated rpm. I am running a spark plug gap of .045" with a Pertronix electronic ignition module and 'hot' coil on my '51 H. You'll be impressed with how much easier it starts.

The magneto has no centrifugal advance - only a fixed ignition retard built into the impulse coupling. (It retards timing only at cranking speeds.) Therefore there are no centrifugal advance parts in a mag that can be transplanted into a distributor.

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As JimN and NDS point an A distributor will work fine on an M. It might cause the M to develop just a tad less power - probably not enough less to notice however. It also MIGHT cause an increased tendency to backfire on a sudden throttle closure. But then so does the "correct" distributor as the advance parts wear - so it's really not a big deal.

If it were mine go ahead and use it...

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A word of caution on your high voltage coil: The 40KV coil will indeed fire .040 plug gap. HOWEVER the distributor is designed for lower voltage (20KV or less). So long as the cap and rotor are in good shape and clean it'll work fine. But the HV coil and the wide plug gap may result in arcing inside the cap (and consequential misfiring) as the cap ages, accumulates internal dust and moisture, etc. Bottom line is you may be better off using a conventional coil and standard plug gap with your electronic ignition.

(quoted from post at 11:19:27 10/28/08) As mentioned earlier, the advance is different but not much. The tractor magnetos had a 35° advance, the ag distributors have 40°.

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The advance available in the distributor is determined by the size of the hole in the plate to which the weights attach. A plate stamped 22R would have 22 degrees of distributor advance designed to run right hand rotation. Crankshaft degrees will be twice the amount of distributor degrees.

Yeah, what Owen said. The rate and speed at which the advance comes in is determined by the springs. Unless someone has been swapping internal parts around, you can tell which version you have by the code letter stamped into the distributor mounting flange (not the battery ignition unit flange).

The early distributor for the A was code A, the same as the M used. Later A distributor was code J.

Wrights salvage in Quincy Illinois has two Farmall tractors,one a c and one an h, they both use GM hei distrubuters Right angle drive on the dist drive. Looks funny But works. Bernie Steffen

Yes.