Question 12 MODE01 - Chief MODU Engineer

The Correct Answer is A. **Explanation for A (less cold valve lash):** Valve lash is the small clearance (gap) between the valve stem tip and the rocker arm (or cam follower) when the engine is cold. This clearance is necessary to ensure the valve fully seats even when the engine is hot and the components have thermally expanded. If the valve seats in the cylinder head are worn, material is effectively removed. This causes the valve to sit **higher** in the cylinder head (recess further into the head) when it is closed. Because the valve stem is pushed further up toward the rocker arm, the distance between the rocker arm and the tip of the valve stem is reduced. This results in a **smaller** valve lash, or **less cold valve lash**. If the wear is significant enough, the clearance could be entirely eliminated, causing the valve to "hang open" even when the engine is cold. **Why the other options are incorrect:** * **B) more cold valve lash:** This is the opposite of what happens. Worn seats cause the valve to recess, thereby reducing the clearance, not increasing it. * **C) excessive pressure in hydraulic valve lash adjusters:** Worn seats affect the mechanical positioning of the valve stem. While this change in position might be compensated for by the hydraulic lash adjuster (HLEA or lifter), it does not inherently cause *excessive pressure* within the adjuster itself. The hydraulic adjusters maintain a zero-lash condition based on oil pressure and bleed-down rates, which are not directly altered by the physical wear of the valve seat. * **D) broken valve springs:** Broken valve springs are typically caused by factors such as excessive engine speed (valve float), material fatigue, or coil bind (running out of usable spring travel). Worn valve seats change the static position of the valve but do not introduce forces or movements that would typically lead to spring failure.