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Four Stroke Engine

Contributed By: Enginebasics.com

A four-stroke engine has four main strokes to its cycle.

The first stroke, called the intake stroke, the crankshaft pulls down the piston by rotating. The intake valve is open at this point in the cycle, and air will be pulled through the intake manifold into the motor. After this is complete the camshaft rotates to the low spot on the lobe. This allows the valve spring to close the intake valve.

The second stroke is called the compression stroke. This is because it compresses the fuel/air mixture. While this is happing the intake and exhaust valves are closed.

The third stroke is called the power stroke. Right before the piston/crankshaft reaches the top dead center, or known as the TDC, the spark plug fires. This ignites the fuel air mixture, which then forces the piston downward. In the motion of the piston being propelled downward the crankshaft is turned. This is the only cycle where power is produced.

The fourth and final stroke is called the exhaust stroke. Once the stroke begins upward, the camshaft opens the exhaust valve, and the piston is propelled upward by the crankshaft, pushing the burnt fuel air mixture out of the exhaust. That is the basics of how a four-stroke motor works. The diagram found below will help you visually put the 4 strokes together to see the combustion cycle of a 4 stroke engine.

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