🔍 Key Concepts

• Relationship between spring tension and the pressure needed to lift valve I off its seat • How changing the length of stem III affects when the starting air control begins to move the valve • The meaning of advancing timing in an air start system (air admitted earlier in the crank angle)

💭 Think About

• If you want the valve to open earlier, do you want it to open at a higher or lower control air pressure acting on the top of the piston? • Does tightening or loosening spring II make it easier or harder for the valve to lift at a given pressure? • If stem III is made longer or shorter, does the operating lever begin to move the valve sooner or later in its travel?

✅ Before You Answer

• Trace the force balance on valve I: control air pressure vs spring II compression • Look at how motion is transmitted through stem III and where free play/clearance might be adjusted • Decide which adjustment causes the valve to start to lift at a smaller crank angle (earlier in the stroke), which is what "advance" means