🔍 Key Concepts

• Purpose of an exhaust valve spring in a diesel engine valve train • How a camshaft lobe moves the valve from closed to open and back • The idea of preload or initial tension on a spring in machinery

💭 Think About

• Think about what the valve spring must do when the valve is fully closed at maximum cylinder pressure—does the spring need to be relaxed or pushing hard? • As the cam lobe rotates and starts to lift the valve, what happens to the length of the spring—does it stay the same, get longer, or shorter? • Is a valve spring designed to ever go completely loose (no compression), or is there always some force on it to control the valve motion?

✅ Before You Answer

• Check whether a valve spring needs some compression even when the valve is closed to keep it tightly seated. • Consider whether the spring force should be greater, less, or the same when the valve is open compared to closed. • Verify if in real engine design a valve spring is ever allowed to be totally unloaded (no tension or compression) during the cam cycle.