In a normally operating engine, intake and exhaust valves are opened by a cam and closed by the __.
a. Rocker arms or cam follower
b. Valve spring
c. Lifters (tappets)
d. Valve guide and/or pushrod
The correct answer and explanation is :
The correct answer is b. Valve spring.
Explanation:
In an internal combustion engine, the intake and exhaust valves play a crucial role in controlling the flow of the air-fuel mixture into the combustion chamber and the expulsion of exhaust gases. These valves are controlled by the camshaft, which rotates in sync with the engine’s crankshaft. The camshaft has specially shaped lobes that open and close the valves at the correct time during the engine’s operating cycle.
While the camshaft is responsible for opening the valves, the valves are closed by the valve springs. Valve springs are designed to provide the necessary force to push the valve back into its seat after it has been pushed open by the cam lobe. Here’s how it works:
- Opening the Valve: The cam lobe pushes against the rocker arm or cam follower, which, in turn, pushes on the valve stem, causing the valve to open. This allows the air-fuel mixture to enter the combustion chamber (intake valve) or allows exhaust gases to exit the combustion chamber (exhaust valve).
- Closing the Valve: Once the cam lobe moves past the point of maximum lift, the valve spring takes over. The spring exerts a force on the valve, pushing it back into the closed position, sealing the combustion chamber and preventing any further flow.
The valve spring is essential in maintaining the timing of the valve’s closing action, ensuring that the valve remains seated until it is needed to open again. Without a valve spring, the valve would remain open after the cam lobe passes, disrupting the engine’s timing and performance.
Other options like rocker arms or cam followers, lifters (tappets), and valve guides or pushrods play roles in transmitting motion or guiding the valve, but they do not provide the force necessary to close the valve. The spring is the key component for valve closure, which is why valve springs are essential in a normally operating engine.