🔍 Key Concepts

• four-stroke diesel cycle (intake, compression, power, exhaust) • what makes a valve move back to the closed position after the cam has stopped pushing it • the difference between opening force (cam/lifter) and return force (spring)

💭 Think About

• When the cam lobe rotates away from the valve, what force brings the valve back toward its seat? • If there were no valve spring, what could happen to the valve during compression or power stroke? • Which answer choice describes what happens every time the cam is no longer acting on the valve?

✅ Before You Answer

• Identify which part actually opens the valve (cam/follower vs. spring). • Think about which option describes a function that must occur on every stroke where the valve is not meant to be open. • Eliminate any choices that suggest the spring’s job is to hold the valve open or to act only during one specific stroke.