Oilers/Plant Tenders (HHC) Civil Service Practice Exam

In a poppet valve engine, which parts require lubrication?

1. Air intake manifold

2. Exhaust system

3. Cam and tappet mechanism and the valve stem

4. Fuel injection system

The correct answer is: Cam and tappet mechanism and the valve stem

In a poppet valve engine, the cam and tappet mechanism and the valve stem are critical components that require lubrication for several reasons. The camshaft and tappet system operate together to control the opening and closing of the poppet valves. As the cam rotates, it pushes against the tappets to move the valve stems and allow air-fuel mixture in or exhaust gases out. This mechanism experiences high friction, and without proper lubrication, it can lead to excessive wear, heat buildup, and potential engine failure. Lubrication in this context ensures smooth operation, reduces wear and tear, and helps dissipate heat generated during operation. The lubricant creates a film that minimizes direct metal-on-metal contact, thereby enhancing the longevity and efficiency of the engine. The valve stems also require lubrication to reduce friction where they slide through the valve guides, ensuring easy movement and preventing binding. While other components of the engine, such as the air intake manifold, exhaust system, and fuel injection system, have specific maintenance needs, they do not require direct lubrication in the same manner as the cam and tappet mechanism and valve stems. Therefore, understanding the lubrication needs of the key moving parts in the engine is vital for optimal performance.