The Internal Combustion Engine

 The engine in the 172 is a four cylinder, horizontally opposed configuration. There are many different models of engines as well as engine sizes that can be found in the various models of the 172.

One example is the O-320 Lycoming: The "O" stands for Opposed. (horizontally opposed)
This means that the cylinders are situated across from each other.
The "320" stands for 320 cubic inches of displacement. What this means is that the combustion cylinders of the engine are cylindrical in shape. If you were to compute the volume of each cylinder and add all cylinders together, they would add to 320 cubic inches.

Lycoming is the manufacturer's name.
Let's examine the operation of the engine.
The engine works on the principle of compression and expansion of air. The surrounding air is pulled into the engine where it is filtered upon entry by means of the air filter. This filter element takes out all but the smallest of debris particles. The filtering is necessary in order to preserve the cleanliness of the internal workings of the engine. Debris entering the engine can lead to premature wear of engine components and eventually engine failure. The air then continues into the carburetor where it is mixed with atomized fuel. The fuel-air mixture then passes into the cylinders through the intake valves. These valves are opened precisely at the correct time by means of a cam shaft.

The piston is moved by means of a crankshaft fitted into the engine block along the horizontal axis. The crankshaft is a shaft with offset throws. These throws are able to move the pistons when the shaft is rotated. (see engine animation)
These throws work with the same principle as a bicycle crank.

     *Imagine yourself riding a bicycle. Your knee caps would represent the pistons while your legs represent the connecting rods. (The connecting      rods do just that, connect the pistons to the crankshaft.) As the bicyle crank turns, each leg alternates rising and falling, which imitates the      actions (or strokes) of the pistons.

The combustion cycle is comprised of 4 different strokes, they are as follows:
  1. Intake stroke
  2. Compression stroke
  3. Power Stroke
  4. Exhaust Stroke
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