Question 8 AEL01 - Assistant Engineer - Limited

The Correct Answer is C ### Why Option C ("valve lash adjusters") is correct: The valve stem, cylinder head, and block all expand as the engine warms up. This expansion reduces the clearance (known as valve lash) between the end of the valve stem and the rocker arm (or cam lobe, in an overhead cam design). If this clearance were to completely disappear or become negative, the valve would be held slightly open, leading to compression loss and burnt valves. **Valve lash adjusters**, particularly modern **hydraulic valve lash adjusters (also known as hydraulic lifters or followers)**, automatically maintain zero or near-zero clearance between the cam and the valve train components across all operating temperatures. By constantly compensating for thermal expansion and contraction, they ensure the valves open and close properly throughout the engine's warm-up cycle. ### Why the other options are incorrect: **A) valve springs:** Valve springs are crucial for closing the valves quickly and keeping them sealed against the valve seat. They provide the force necessary for valve closure but do not compensate for changes in the physical length of the valve stem or engine components due to temperature changes. **B) hydraulic governor:** A hydraulic governor (typically found in automatic transmissions or some fuel injection pumps) is used to regulate engine speed or control shifting points. It has no function related to compensating for thermal expansion in the engine's valve train. **D) cooling system:** The cooling system’s primary function is to manage and dissipate heat generated by combustion to maintain the engine at its optimal operating temperature. While it controls the overall temperature (and thus the extent of thermal expansion), it is a passive control mechanism for this issue; it does not contain components that actively adjust the mechanical clearance in the valve train to allow for the expansion that occurs during warm-up.