🔍 Key Concepts

• Valve train components in a four-stroke diesel: cam, push rod, rocker arm, valve, and valve spring • How a valve moves open vs. how it returns to the closed (seated) position • Difference between forces from springs and from gas/air pressure inside the cylinder

💭 Think About

• Look closely at the parts directly surrounding the valve stem in the illustration—what component would push the valve back against its seat when the rocker arm is no longer pressing it? • When the piston moves and cylinder pressure changes during the cycle, does that pressure reliably close the valve in every stroke, or is a dedicated mechanical device used? • Which of the listed choices is designed specifically to provide a constant closing force on the valve, even when there is no pressure in the cylinder?

✅ Before You Answer

• Identify the coiled component around the valve stem and consider its purpose in the mechanism. • Ask yourself which option would still seat the valve when the engine is stopped and there is no gas or air pressure. • Confirm which listed item is intended to hold the valve tightly against its seat to maintain a gas-tight seal.