Cole Farm Equipment, Inc.

There is more to an engine running than putting gas in it and taking off. If you want to know more, that is why we created this section. Below is basic information on how an engine operates. Right now, this only covers 4-cycle gas engines, since they are more prevalent. This section is not meant to prepare you for working on engines (you should not attempt that unless you know what you are doing), but to give you rudimentary knowledge of how they run. In the future, we will expand to cover more types of engines, as well as adding more information in general.

Gasoline powered engines are known as internal combustion. In other words, they run by having tiny controlled explosions occur inside of them. This is a fairly simple procedure, but there are numerous steps involved. Let's start with the fuel.

Fuel is brought into the carburetor, usually by gravity or suction (a fuel pump or diaphragm). Inside the carburetor, the gas is mixed with air drawn in from outside through the air filter. This is an important step, because only gas vapor burns, not the liquid. Once the fuel and air are mixed in the proper ratio, the mixture moves into the combustion chamber, or cylinder.
Inside the cylinder, the air-fuel mixture is compressed by the piston. The mixture is then ignited by the spark plug. This causes the explosion, and drives the piston down. The downward motion of the piston causes the crankshaft to turn. The crankshaft then transfers the power to whatever is attached to it (in most cases, a deck and transmission) and (along with the flywheel) keeps the piston moving.
For a short demonstration of this, click here.

Now, that is the basic operation of the engine, but there is much more involved than just the above. For example:

Oil is essential for the engine to run. It helps keep the engine clean (which is why it needs to be changed regularly) and it takes heat away from the cylinder area to keep it cool.
The flywheel, as mentioned above, helps the crankshaft to keep turning, but it does more. It has fins on it, which force air to move in and around the engine, providing another source of cooling. The flywheel also powers the coil.
The coil or module is what makes the spark plug spark. It contains coils of wire which, when passed by the flywheel magnets, produce current. This current then travels to the plug, and start the combustion.
The alternator, if equipped, is what charges the battery, and, in most cases, keeps you from having to charge the battery manually.

This is really just the tip of the iceburg, as technology improves, so do engines. Many are now coming equipped with fuel injectors instead of carburetors. This does give you the basic theory of operation.