This article is from a tractor website but the question is valid when you are building an early hot rod
Magneto or distributor: which do you choose?
A defining trait of the antique tractor is its lack of a conventional battery. One of the first things to know when trouble shooting, restoring or buying, is where its power comes from – is there a battery or not?
At one point, the answer was probably as simple as checking a model, date or serial number. But since so many machines have been modified to convert from magnetos to distributors, those methods might be a little out of date today. Nevertheless, understanding where your tractor’s power comes from is critical to knowing which replacement parts to buy – and to decide if converting to a different power style is worthwhile.
To review, every gas-powered engine needs two essential things to start, a spark and fuel. The spark fires the spark plugs in rhythm, igniting the gas in the combustion chamber. The question as it relates to this post is where that spark comes from.
The main difference between a magneto and a distributor is that a mag is self-contained & DOESN’T need a battery to produce a spark. A distributor, on the other hand, requires an external power source to operate.
Magneto technology has been around for a long time. The unit is essentially a distributor with a generator built in – it still has a coil, it still has a set of points and condenser and it still has a spark rotor and distributor cap. When tractors first came into being, batteries were not part of the picture, so operators needed to hand crank a generator, which then provided power to the tractor.
Magnetos have proven to be a reliable way to run a tractor, and a well-built magneto can produce a similar amount of spark compared to an electrical system. They also have been, historically, easier to come by. In fact, during World War II, tractors that were originally built to be battery powered were switched back to magneto technology due to battery shortages.
(Of note, magnetos can work in conjunction with batteries as well, providing self-produced power to the tractor when the battery dies, but does not require one).
Of course, this is not to say that battery-powered systems don’t have their advantages. Nothing beats the convenience of electric start and most distributors simply produce a stronger spark than magnetos. In addition, distributors can give you the extra power needed to run auxiliaries such as headlights. They are also, generally, easier to maintain and understand for most people.
An alternator is also, then, required to re-charge the battery in an electrical system.
What do you prefer on your tractors? Do you use a magneto, or is yours battery-powered? Have you thought about converting? Tell us below.
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