'40 Farmall H

Rwverde

New User
Hey guys, my parents have a 40 farmall H that I'm trying to get running for them. They have a farm and have been without the tractor for years now. I guess my dad didn't do his research on the tractor when he bought it and messed up a lot of the electronics for it. He didn't know it was a 6v pos-earth system I guess.

So far, I've gone and rewired the whole beast and plan to convert it to 12v neg-earth. I have the alternator already fabbed up and installed now I just need some help with the coil. Initially, my dad told me that it was missing the coil and so I did my research and ordered an ignition coil(12v) and it turns out that it is in fact not missing an ignition coil, but a magneto coil. Is there any way to convert it from the magneto coil to the ignition coil that I have already ordered and even received now? I'd really rather not have to send it back and get the magneto.

Thanks for any help guys!
 
Buy a distributor or drill a hole for coil wire and
convert the mag ,I don't like messing up a mag but
it's yours . I would fix that mag properly or buy a
distributor.
 
(quoted from post at 22:13:48 03/20/15) Buy a distributor or drill a hole for coil wire and
convert the mag ,I don't like messing up a mag but
it's yours . I would fix that mag properly or buy a
distributor.

I'm sure a lot of people would agree with you on that but in this case, the tractor only serves a functional purpose. It's not worth much and it wouldn't be worth restoring in my opinion. However, it's not even functioning at this time and I just want to get it up and running with whatever I've got.

It has a distributor cap, and the mag is behind it. Isn't that a distributor? Why would I need buy another distributor? I read somewhere that I can convert a mag to ignition coil by taking the wire from the tower or something? I didn't quite understand it. Maybe that's what you're trying to say? Could you explain it in a bit more detail please?

Thanks!
 
A mag and a distributor are 2 different things. They look somewhat similar. A mag is designed for a tractor with no electrical system and if yours is working you can keep it and still have a 12 volt system for your starter and lights. If the mag is not working then the question is does it need new points and condenser (which has to work no matter what) or is the internal coil bad. You can replace the coil or you can add an external coil which you have already bought and make the mag work like a distributor.I don't recall exactly the wiring for that, especially if you are adding an alternator but I'm sure some guys will add to this tread and tell you how it has to go.
 
Here are a few differnt pictures of Mag verse Battery ignition. The third picture is the Delco conversion. My 2 cents "fix it correctly and get the correct coil.
a187062.jpg

a187063.jpg

a187064.jpg
 
I agree with the idea of repairing the mag, or replacing it with a IH distributor. But the question you asked is as follows:
Because the coil is gone, things get some easier.
Remove the cap. The rotor is geared to the mag cam shaft. It has marked teeth using bevel cuts and or other marks to align the gears (mandatory timing issue here)
rotate the engine to get the marks aligned (tiny and might need visual magnification to see)
Remove the rotor and the plate holding the rotor shaft to gain access to the points. Run a wire from the points (movable) to the terminal on the side of the mag (no other connection) Set the point gap at .013" on a high point of the cam.
Replace the plate and rotor.
Install an ignition coil designed for 12volt operation with no external resistor. (NAPA or other parts store)
Connect the negative terminal of the coil to the "MAG" terminal to which you connected the points.
Connect the positive to a (different) ignition switch A simple toggle SPST will work. The original switch is a mag switch and grounds the mag to stop the engine, or does not exist. (early tractors had a cable connected mechanical grounding control. The new switch will go to the amp gauge to get 12v.
A condenser (matching the coil) for the system must also be placed in the circuit. It can be connected to the coil at the negative terminal and the body of the condenser grounded. A coil wire is used to connect the high voltage to the center terminal of the cap.
This will make the existing "MAG" into a distributor. but will not be as smooth as a distributor with timing advance control. If the mag impulse coupling does not snap when cranking, this system will not work. It must have the impulse coupling to allow starting, and the reasonable advance when it starts. Jim
 
From what I'm gathering, all of this information you're providing me with is under the assumption that the mag is still there. The problem is, it's not. My oldest brother tried to fix it years ago and since then it has been lost.

I'm guessing that I will end up having to purchase a mag for it. Will a mag coil work with my 12v conversion? Will I need to run a resistor?
 
No power goes to a mag ever. No resistor is used as a mag is a generator of electricity.
I recommend a standard IH distributor, a smaller investment than a mag, and better for smooth operation because it has centrifugal advance. Many distributors look the same, just get one from the H series tractors (or W4) to assure it has the correct rotation and advance. Jim
 
First, Your posts totally contradict themselves. First you say everything is there except the coil and then you say everything is missing. Which is it?

Second, I suggest you do a little more google searching and learn the basic difference between a magneto ignition system and the delco distributer ignition system principles invented by Charles Kettering.

Magneto: A mag generates its own electrical power for the ignition system. The one wire going to a mag is simply a ground out wire that shorts it out to kill it. In other words the tractor battery supplies no power whatsoever to the ignition system. So if the tractor is 6 volt, 12 volt, 24 volt etc it will not matter to the mag as it is its own self contained power generating unit totally isolated from the battery. Tractors that are hand crank and lack electric start will defiinitely be mags. That said tractors can be electric start and still have a mag as well.

A Delco type distributer: The battery supplies power to provide the spark in this system. You may or may not need a resistor for the coil depending on the coil type used and the tractor battery voltage used.

Hillbilly hodgepodge system: It is possibile to do a hillbilly Charles kettering ignition conversion to an otherwise non-functioning magneto. This is done so the battery can supply power to a mag that has bad magnets or other problems that hinder it unable to generate its own power for the ignition. It is a cheap fix compared to having a mag rebuilt to correct its problems. I would not convert a rare mag, but a common one that is valueless then who cares.

Disadvantage to any magneto system is that there is no spark advance for different rpm ranges when the tractor engine is running. Basically spark advance is optimized for the wide open throttle setting only and is less than optimum anywhere else in throttle range. In short tractor runs slightly less good at partial throttle settings due to this.

Distributer systems often have centrifugal weights that automatically adjust spark advance within the distributer based on engine rpm. So the spark timing is real close to perfect for every rpm range on the tractor instead of just at the one WOT like a mag.

If everything is missing on your tractor then buy a used disributer as it is the far superior system to a mag. No way would I buy a used mag unless I wanted the tractor to operate without a battery.

I have no idea how you could be correcting all the wiring woes on your tractor when you do not even understand what you have: Search Bob M diagrams on this site for very helpful wiring diagrams for each type of ignition system when doing 12 volt conversion.
 
Call me hillbillie or any other name. I have converted mags to distributor by just using the mag frame and points. I would do it again but a magneto coil is not terribly expensive and will last as long as you need it. Only disadvantage to such a conversion is the price of magneto points seem to be more costly. I really like the Delco distributor better than the IHC
 

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