within the cylinder. The relationship between volume, pressure, and temperature within a cylinder of the engine is explained in the chart below and shown in figure 2-2. Note the changes within the cylinder while the temperature outside remains a constant 70F.

This up-and-down motion is known as RECIPROCATING MOTION. This motion (straight-line motion) must be changed into ROTARY

Figure 2-2. - Volume, pressure, and temperature relationships.

MOTION (turning motion) to turn the wheels of a vehicle. A crankshaft and a connecting rod change their reciprocating motion to rotary motion.

All internal combustion engines, whether gasoline or diesel, are basically the same. We can best demonstrate this by saying they all rely on three things - FUEL, AIR, and IGNITION.

FUEL contains potential energy for operating the engine; AIR contains the oxygen necessary for combustion; and IGNITION starts combustion. Each one is fundamental, and an engine cannot operate without them. Any discussion of engines must be based on these three factors and the steps and mechanisms involved in delivering them to the combustion chamber at the proper time.

DEVELOPMENT OF POWER

The power of an internal combustion engine comes from burning a mixture of fuel and air in a small, enclosed space. When this mixture bums, it expands greatly, and the push or pressure created is used to move the piston, thereby rotating the crankshaft. This motion is eventually sent to the wheels that move the vehicle.

Since similar action occurs in each cylinder of an engine, let's use one cylinder to describe the steps in the development of power. The one-cylinder engine consists of four basic parts, as shown in figure 2-3.

First, we must have a CYLINDER that is closed at one end; this cylinder is similar to a tall metal can that is stationary within the engine block.

Inside this cylinder is the PISTON - a movable plug. It fits snugly into the cylinder but can still slide up and down easily. This piston movement is caused by fuel burning in the cylinder and results in production of reciprocating motion.

You have already learned that the up-and-down movement of the piston is called reciprocating motion. This motion must be changed into rotary motion, so the wheels or tracks of a vehicle can rotate. This change is accomplished by a throw on the CRANKSHAFT and the CONNECTING ROD which connects the piston and crankshaft throw.

The throw is an offset section of the crankshaft that scribes a circle, as the shaft rotates. The top end of the connecting rod is connected to the piston and must therefore go up and down. The lower end of the connecting rod is attached to the Crankshaft. The lower end of the connecting rod also, moves up and down but,