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The Model T Ford ignition system remained the same throughout the 19 years of production, even though the electrical system was supplemented with a starter, generator and electric lighting in 1919. Henry Ford designed the car with an internal magneto coil and magnet system, fixed to the flywheel of the engine. The magneto provides current to the four ignition coils, one for each cylinder, which in turn intensify the electrical charge to create a strong spark at the spark plug. The discharge from the coil is triggered by collapsing the coil field by earthing the each coil at the correct time by the timer, (commutator) mounted on the end of the camshaft on the front of the engine.
The assembly is made up of 16 iron cores, wound with copper ribbon and linked to the coil next to it in a continual loop and terminating at the magneto post fitted to the top of the transmission cover. These coils are fitted to a ring which is in turn fixed permanently to the engine block. The flywheel has 16 “v” shaped magnets bolted to it, each magnet pole (north or south) sits next to the same pole of the neighbouring magnet. As the flywheel (and magnets) turn, they pass the iron cores in the ring, the magnetic field inducing a current through the coil ring circuit up to the magneto post. The faster the flywheel spins, the higher the current produced. See the pictures below:
Each Model T Ford runs using four coils, one per cylinder, housed in a box that features contact points for a power supply in, contact point to the timer for each coil via a wiring loom and a contact terminal for the spark plug lead. The style and location of coil boxes changed throughout the years the Model T was produced, but all do the same thing (with the early models including the ignition switch)with the style and location of the box also changing.
Each coil assembly is housed in a finger jointed timber box, filled (originally) with tar or pitch as its also known. This tar, not only holds the components in place, but adds to waterproofing and insulating the parts from each other. The parts inside include a primary winding, a secondary winding, a condenser, connecting wires and a piece of glass to divide the components.
In the early cars, there was no battery or starting system provided, so the power supply to the coils magnified to create the spark at the plug leads, was solely produced by the magneto system. This meant that to start the car, the magneto and all the associated ignition systems must be in good condition and correctly cleaned and adjusted.
When the driver hand cranked the engine, they produced sufficient rotation of the magneto on the flywheel to generate the current to the coils. Once started the engine obviously maintained this rotation and the ignition system became self supporting in operation.
In later vehicles, fitted with a dry cell (in the day) battery and or electrical starting system, the car could be started either by switching to the magneto system and starting as above, or, to battery, where the battery provided…