in a normally operating engine, intake and exhaust valves are opened by a cam and closed by the _
The Correct Answer and Explanation is:
Correct Answer: Valve Springs
In a normally operating internal combustion engine, the intake and exhaust valves are opened by the camshaft lobes and closed by valve springs.
Explanation:
The camshaft is an essential component of the engine’s valve train. It controls the timing and movement of the intake and exhaust valves. As the camshaft rotates, its lobes push against the valve lifters, rocker arms, or tappets, depending on the engine design. This action opens the valves at precisely timed intervals to allow air-fuel mixture to enter (intake valves) or exhaust gases to exit (exhaust valves) the combustion chamber.
The role of the valve springs is equally critical. Valve springs are tightly coiled components that are installed around the valve stem and press the valve closed when the cam lobe moves away. These springs are designed with sufficient tension to overcome the forces acting against the valve, such as the inertia of the valve train components and the pressure from the combustion process inside the cylinder.
Why Valve Springs Are Crucial:
- Valve Closing: The springs ensure that the valves close firmly and quickly after being opened by the camshaft. This prevents the loss of compression and maintains efficient engine operation.
- Maintaining Valve Timing: By keeping the valves in contact with the camshaft lobes, the springs prevent valve “float” or loss of control at high engine speeds, where the inertia of the moving components can cause the valves to stay open longer than intended.
- Durability: Engine valve springs are designed to withstand the stresses of millions of cycles without failure, ensuring long-term reliability.
A failure in the valve spring could lead to serious engine problems, such as misfiring, loss of power, or even damage to the engine if the valve contacts the piston. Thus, valve springs play an indispensable role in the engine’s operation, working in harmony with the camshaft to maintain proper timing and performance.