🔍 Key Concepts

• Thermal expansion of metal parts in an engine as temperature increases • Purpose of valve lash (clearance) between the rocker arm and valve stem • How engines maintain proper valve timing and sealing as temperature changes

💭 Think About

• When metal valve stems get longer as they heat up, what would happen to the valve operation if nothing compensated for that change? • Which of these choices directly relates to a small, intentional clearance in the valve train that can change as parts expand? • Do all of the listed systems act on the individual valve stem length, or do some control something more general, like speed or cooling?

✅ Before You Answer

• Identify which option is specifically about mechanical clearance in the valve train, not force or cooling. • Ask yourself: which choice exists mainly so that at normal operating temperature the valves open and close fully without staying slightly open? • Eliminate any options that act on overall engine speed or temperature rather than on the valve-to-rocker mechanical gap.