THE ENGINE: Now let's discuss the engine itself. As we can see in the diagram, in the gasoline engine the air and fuel mixture is drawn in from the carburetor or fuel injection system and is delivered through the intake valve into the combustion chamber. As the piston forces the air and fuel mixture together, the spark plug ignites and causes an explosion. This forces the piston back down into the engine, where this force is translated into rotary motion at the crank shaft. The intake valves and exhaust valves regulate the amount of air fuel mixture that enters the cylinders and exits. This timing, that is when the valves open and close, is regulated by the cam shaft and valve lifters. Together with the push rods and rocker arms, they make sure the valves open and close at the proper time. The main bearings hold the crank shaft to the engine block and allow it to rotate, while the piston range maintains pressure in the combustion chamber. An overhead cam engine eliminates push rods and rocker arms by mounting the cam shaft above the valves and cylinders, thus giving the engine more power.
