I have had a couple of times where I had some dramatic failures occur on my Tractor engines. One time I had a chain snap and the chain made a ferocious clunk and then fell off the Tractor. The funny thing is that the engine kept running, and I had to shut it off.
I replaced the chain and ran into a peculiar problem. The engine would not start.
This is where most of us, with NO engine experience just throw up our hands and kick the Tractor and go away. Then we throw it in the back of the pickup and bring it over to "Smokin Joes Lawnmower Repair." There we spend about $200 to have the engine fixed.
I am here to tell you forget about going to "Smokin Joes.
First of all a basic understanding of ignition systems is required. (I am assuming that you understand the Otto Cycle or 4 cycle engine theory, so I will dispense with that SnoozeVille explanation)
Ignition systems are basically partial generators. The flywheel has a magnet, and the Magneto has a coil of wire in it. The theory behind electric current is that when a wire (a simple wire ) is passed through a magnetic field that an electric current is induced into the wire.
And conversely, when a wire is induced with an electric current it gives off a magnetic field.
The Magneto (the device that the spark plug wire comes out of) has a coil of wire in it plus a core of iron to attract or concentrate the magnetic flux lines into the wire.
The wire then gets an instantaneous jump in electricity as the magnetic field in the flywheel passes by it. The sudden increase in electricity is concentrated as high voltage which is released as a spark in the spark plug.
The timing, or the firing of the electricity to the spark plug is regulated by circuitry. This particular circuitry is activated by a small magnetic sensing switch (which looks like a small cylinder of steel tucked in with the coil). When the magnet passes by the magnetic field activates the switch. The switch then releases the coil energy into the spark plug.
The spark plug is nothing more than a glorified jumping bridge for electricity. We all are familiar with this static discharge when we scrub our feet against the floor and the reach out and touch somebody. A spark jumps when we get close, like .125 inches and closer.
The design of the spark plug is to keep the electricity isolated up to the bridge. Once the electricity from behind shoves real hard, it forces the electrons in front to jump. Kind of like getting pushed off of a bridge.
So the white part of the spark plug is non-conductive and an insulator. The metal part is isolated from the rest of the spark plug and only becomes integral when spark completes the circuit or jumps across the gap.
Obviously, sparks cause the right concentration of Oxygen and Combustible gases or even dust, to ignite. Ignition is the excited state of electrons jumping from one molecule to another. This excited state releases heat and light: we call that flame or ionized gas.
Next time we will discuss how to trouble shoot the ignition system so that you do not have to pay Smokin Joes what you just have learned...and will learn.
