Magneto vs. Distributor

Fri Mar 15, 2013 9:58 am

My all original (so far) '47 Cub has a magneto & distributor ignition. However the later models only have a distributor.

Was a magneto essentially unneccessary when hand cranks became a thing of the past?

What's the difference between a magneto and a distributor? Since my tractor has both, I presume they're not that closely related. What makes the latest models not need a magneto?

For what it's worth, I'm going to be converting this tractor to 12V and wondering if I want to keep the current magneto/distributor combo or go with a later distributor only setup. BTW, I don't ever plan to hand crank this thing.

Re: Magneto vs. Distributor

Fri Mar 15, 2013 10:41 am

Unless you've got something very strange, you have one or the other, not both.

Both magneto and distributors have a distributor cap and wires. Perhaps that is where your confusion is?

The difference is that a magneto generates its own electricity. A distributor uses battery power to make the spark.

The reason they went to a distributor is because it's less maintenance and cheaper to build.

Re: Magneto vs. Distributor

Fri Mar 15, 2013 10:42 am

The magneto has a distributor cap, so that it can distribute power to the individual spark plugs It is not the same as a regular distributor. The reason a magneto was used was for the base model tractors that did not have headlights or electric start, is that the magneto generates spark mechanically therefore the tractor could operate without a battery. Also, that was the technology of the day, and as many can attest, they still work today with little problems.

With the addition of electric start and headlights, the magneto still provides spark for the engine, and the generator charges the battery. That's it, and the two sides of the electrical system do not really interact. This tractor will still operate without a battery, however the starter and lights will not function.

When you change to 12v power, you need a coil, starter, generator(or alternator), regulator, etc., and a wiring harness that provides all the wiring to put everything together. The tractor will not operate without a battery or if the battery dies.

Personally, If I had a 1947 tractor that was basically complete, I would fix up the magneto system and keep it original. There's not any real benefit in going to 12v system, other than light bulbs are less expensive and you can jump start it from a car. The down side of going to a 12v system is buying all new components, rewiring everything, fitting in new components, etc. You're probably looking at a couple hundred bucks just for the distributor and alternator alone, not including all the other components you will need. On the other hand, you can probably get a magneto rebuilt for $100, and re-use everything you already have.

If the tractor is tuned properly, it will start, run, operate exactly the same, 6v magneto, or 12v battery. Anyway, just my thoughts.

Re: Magneto vs. Distributor

Fri Mar 15, 2013 12:16 pm

In many ways the magneto is BETTER than a battery ignition. A good magneto will provide a hotter spark than a battery ignition can ever hope to make. A magneto will let the tractor start even though the battery is dead.

Now don't quote me on this but I *think* that battery ignitions give you better advance capability than a mageneto. The battery ignition can advance the timing further as the RPMs increase, giving you better power and better fuel economy.

Re: Magneto vs. Distributor

Fri Mar 15, 2013 12:28 pm

Pardon my ignorance as I was barely around before everything was EFI.

I think I was led astray by the '47 operators manual that discusses the magneto, and then discusses the distributor gear and distributor cap on the next page. So in this sense, the distributor is part of the overall magneto.

Re: Magneto vs. Distributor

Fri Mar 15, 2013 1:09 pm



Distributor (battery ignition)


Thanks to TM Tractors for the photos

Re: Magneto vs. Distributor

Fri Mar 15, 2013 1:44 pm

I have a magneto on my Cub and just love it. It took some tuning but it'll generally kick over on the first pass of the hand crank (unless it's in a mood, or it's cold out, or its raining, or sometimes when the day ends in 'Y', but I digress). :wink:

My wiring harness was in pretty bad shape when I first got the tractor so crank starting was my only option for a couple of years.

Re: Magneto vs. Distributor

Fri Mar 15, 2013 5:13 pm

The distributor is much more reliable in my opinion. And cheaper to operate. You would do well with a distributor while converting to 12 volt, which is also more reliable. You will hear many say that 6 volts works just as well as long as you keep it serviced on a regular basis. All my cubs are 12 volt, I have few if any trouble starting them even after that have set for 12 months or more. If you want to keep it original go with the mag and 6 volt, if you are going to use it regularly go with the distributor and 12 volt with an alternator.

Re: Magneto vs. Distributor

Fri Mar 15, 2013 7:35 pm

I second Boss on this one.

Re: Magneto vs. Distributor

Fri Mar 15, 2013 9:35 pm

Stick with the mag & 6 volt. IMO :D

Re: Magneto vs. Distributor

Fri Mar 15, 2013 10:22 pm

Thanks for the info guys.

The plan is looking to go to a 12V system with a distributor. It looks like when you add in a core charge, I can get a rebuilt distributor for a little bit more than it would take to have the magneto rebuilt.

I plan to take some time with it tomorrow. Taking a few more electrical items look (bad wiring). Probably end up fixing up the fuel delivery first.

Re: Magneto vs. Distributor

Sat Mar 16, 2013 3:09 pm

Do yourself a favor and save the old stuff.