Question 19 MODE01 - Chief MODU Engineer

The Correct Answer is C ### Explanation of the Correct Option (C) **C) reduce valve gear pounding** Hydraulic valve lifters (or hydraulic tappets) are designed to automatically maintain zero clearance, or zero lash, in the valve train. They achieve this by using engine oil pressure to continuously adjust their internal length, compensating for thermal expansion and wear of the various components (camshaft, pushrods, rocker arms, etc.). By eliminating mechanical clearance (lash), the lifter ensures that the rocker arm makes contact with the valve stem (or pushrod) gently at all times, rather than hammering into a gap. This continuous, cushioned contact significantly reduces mechanical shock, noise, and wear, which is collectively referred to as **reducing valve gear pounding**. ### Explanation of the Incorrect Options **A) create longer valve duration** Valve duration (the length of time the valve is open, measured in degrees of crankshaft rotation) is determined entirely by the profile and shape of the camshaft lobe, not by the type of lifter used. Hydraulic lifters affect the timing and noise level, but not the inherent duration designed into the cam. **B) obtain greater valve lift** Valve lift (the maximum distance the valve opens) is also determined solely by the geometry and maximum height of the camshaft lobe. Hydraulic lifters operate within the constraints of the cam profile and do not increase the maximum lift designed by the engine manufacturer. **D) increase valve operating lash** The primary function of hydraulic valve lifters is the exact opposite: to **eliminate or minimize** valve operating lash (clearance). Increasing lash would lead to excessive noise, reduced valve opening, and increased impact forces (pounding).