When you are troubleshooting electrical or ignition problems on your tractor, one of the first things that you need to know is where the power for your tractor is coming from – either a magneto or a distributor. Since many tractors have been converted from magnetos to distributors, you can’t necessarily rely on the year and model of your tractor to know which one you have. Understanding the basics behind the two systems can help you get the right replacement parts and decide if it’s worthwhile to make a conversion from one to the other.
First, a review. All gas-powered engines need two things to run: gas and spark. To simplify, the spark (electricity) fires the spark plugs in rhythm, igniting the gas in the combustion chamber.
That spark has to come from somewhere – either a stored electricity source (a battery) or a constantly-running electricity source (a generator).
When tractors were first invented, batteries weren’t a part of the picture. Instead, operators hand-cranked a sort of generator inside the tractor. This generator, called a magneto, would then supply electricity for the tractor as long as it was running. Magneto technology has been around for a long time – the little crank you’d turn on an old-fashioned telephone was a magneto, too.
A well-designed magneto can generate plenty of spark, and they are a reliable way to run a tractor. Magnetos have also been (historically, at least) easier to come by than battery-powered systems. During World War 2, even tractors that were normally produced with a battery/distributor combo switched back to magneto technology due to shortages.
Battery-powered systems have their advantages, though. While a well-maintained hand-crank starting system can work very well, nothing beats the convenience of an electric start. Battery-powered systems also have the extra power available to run headlights. In a battery-powered system, a separate distributor moves the electricity from the battery to the engine. An alternator is also necessary to re-charge the battery.
Now, here’s where it gets tricky. Did you notice that I wrote that a battery-powered system has a SEPARATE distributor? That’s because a magneto still has a distributor cap and wires, which sends the power to the individual spark plugs. This is different from the distributor on a battery-powered system, which is a separate part of the tractor.
So – should you switch from a magneto to a distributor, or a distributor to a magneto? Making a switch will most likely involve an entire re-wiring of your tractor. It’s not overly difficult to do so, but it will take time and parts.
Which do you prefer on your antique tractor–a magneto or a distributor? Comment below.