Where is tappet clearance measured in an engine?

Tappet clearance is measured between the valve tip and the rocker pad. This measurement is crucial in ensuring that the engine valves properly open and close without causing damage or inefficient operation.

When the rocker arm pushes down on the valve, it must have a small gap — the tappet clearance — to allow for thermal expansion and ensure that the valve completely seats when closed. If there is too much clearance, it can lead to increased wear and valvetrain noise, while too little clearance can prevent the valve from fully closing, leading to performance issues and potential engine damage.

In this case, measuring the tappet clearance between the valve tip and the rocker pad directly checks the effective contact area where the force from the rocker arm is applied to the valve, making it a critical dimension in maintaining engine performance and longevity.

The other choices do not accurately represent where tappet clearance is conventionally measured, focusing instead on areas that do not directly influence the functional operation of the valve mechanism in the same way.