Understanding the Position of Intake and Exhaust Valves in a Four-Cycle Gas Engine

Which of the following statements correctly describes the position of the intake and exhaust valves during most of the power stage in a four-cycle gas engine?

Answer: The correct statement is option B. The intake valve is open and the exhaust valve is closed.

Both valves are closed during the power stroke. While the fuel is burning in the cylinder, you want all the force of the expanding gases to push the piston down. You don't want any of the gases or their pressure escaping. If either of the valves was open, even just a crack, then part of the gases would escape out the valve, leading to a loss in pressure that is supposed to be pushing the piston.

Which of the following statements correctly describes the position of the intake and exhaust valves during most of the power stage in a four-cycle gas engine?

• A. The intake valve is closed and the exhaust valve is open.
• B. The intake valve is open and the exhaust valve is closed.
• C. Both the intake valve and the exhaust valve are closed.
• D. Both the intake valve and the exhaust valve are open.

Which of the following statements correctly describes the position of the intake and exhaust valves during most of the power stage in a four-cycle gas engine?

The correct statement is option B. The intake valve is open and the exhaust valve is closed.