For the operation and maintenance of your vehicle, it is helpful to understand basic engine technology. Typically, today's cars are built with a four-stroke engine. The four strokes refer to the cycle of intake, compression, combustion (power) and exhaust that occur during rotations of the gasoline or diesel engine.
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The cycle begins when the piston starts at the top dead center (TDC) of the cylinder on its way to the bottom dead center (BDC), the lowest point in the cylinder. On the intake stroke, a mixture of fuel and air is forced into the cylinder through the open intake valve. The exhaust valve is closed at this time. The piston begins its descent, reducing the pressure inside the cylinder. A mixture of fuel and air is drawn into the cylinder through the intake port. The intake valve then closes and the compression stroke begins.
During the compression stroke, the piston begins at the BDC, moving toward the TDC of the cylinder. Both intake and exhaust valves are closed, forcing the air-fuel mixture into a smaller area called the combustion chamber. Just as the piston reaches the TDC, a spark plug fires and ignites the fuel-air mixture, thus forcing the piston down with tremendous force. The resulting pressure of buring gases pushes the piston through to the power stroke until it reaches the BDC. It is this stroke that drives the engine to power the other cylinders and the car.
The exhause stroke is the fourth stage in the four-stroke engine cycle and the piston now begins its upward movement toward the TDC. In this stage, gases remaining in the cylinder from the combustion are removed from the cylinder through the exhaust valve and exhaust port. The gases are forced up to the top of the cylinder as the piston rises and are pushed through the opening, which then closes. The intake stroke starts again to repeat the process once more.
Tech Tip provided by Charles Whitehouse, YATC Lead Technical Instructor