BASIC ENGINE OPERATION
TWO-STROKE ENGINES Two-stroke engines are found in many motorcycles as well as devices such as chain saws and weed cutters. This type of engine only has two strokes or cycles of operation:
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1. Intake/Compression When the piston is at the bottom of its downward travel (bottom dead center), the intake port is uncovered. Air and a mixture of gasoline and oil flow into the cylinder. As the piston moves upward, this mixture is compressed. 2. Power/Exhaust When the piston is near the top of its travel (top dead center), the spark plug “fires,” which ignites the mixture. The pressure from the burning fuel forces the piston downward. As the piston moves downward, it uncovers the exhaust port, which allows burnt gases to escape.
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Two-Stroke Engine Advantages: Powerful, lightweight and simple in construction. Two-stroke engines produce power once every revolution versus four-stroke engines, which produce power every other revolution. Two-Stroke Engine Disadvantages: Requires a mixture of oil and gasoline to operate. Lack of a dedicated lubrication system means twostroke engines do not last as long as four-stroke engines. Difficult to control exhaust emissions.
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