Figure 2-3. - Cylinder, piston, connecting rod, and crankshaft for a one-cylinder engine.

because it is attached to the crankshaft, it must also move in a circle.

When the piston of the engine slides downward because of the pressure of the expanding gases in the cylinder, the upper end of the connecting rod moves downward with the piston in a straight line. The lower end of the connecting rod moves down and in a circular motion at the same time. This moves the throw and, in turn, the throw rotates the crankshaft; this rotation is the desired result. So remember, the crankshaft and connecting rod combination is a mechanism for the purpose of changing straight line, or reciprocating motion to circular, or rotary motion.

FOUR-STROKE-CYCLE ENGINE

Each movement of the piston from top to bottom or from bottom to top is called a stroke. The piston takes two strokes (an up stroke and a down stroke), as the crankshaft makes one complete revolution Figure 2-4

Figure 2-4. - Piston stroke technology.