Question 7 OSE01 - Chief Engineer - OSV

The Correct Answer is B **Explanation for Option B (Correct):** Option B is correct because the exhaust valve operates under significantly higher temperatures than the intake valve. Exhaust gases are extremely hot (combustion heat), causing the exhaust valve and its stem to expand more significantly when the engine is running at operating temperature (hot). Valve clearance is measured cold but is primarily set to ensure sufficient clearance when the engine is hot. To compensate for the greater thermal expansion of the exhaust valve components, the initial cold clearance (the gap measured between the rocker arm and the valve stem tip) must be set **larger** for the exhaust valve than for the intake valve. This ensures that when the engine reaches operating temperature, the exhaust valve stem expands, consumes the extra clearance, and still does not run out of clearance (which would cause the valve to be held slightly open, leading to burning the valve). **Why Other Options Are Incorrect:** * **A) When taken cold, a properly adjusted exhaust valve clearance would definitely be less than the intake valve clearance.** This is incorrect. Setting the exhaust clearance smaller than the intake clearance would result in the exhaust valve losing all clearance and potentially running "tight" or being held open when the engine heats up dueating to excessive thermal expansion. * **C) When taken cold, a properly adjusted exhaust valve clearance would definitely be equal to the intake valve clearance.** This is incorrect. This statement fails to account for the differential thermal loads. Since the exhaust valve experiences much higher temperatures and therefore greater expansion than the intake valve, the cold clearances must be unequal (exhaust > intake) to achieve proper zero/near-zero clearance at operating temperature. * **D) When taken cold, a properly adjusted exhaust valve clearance could be less than or greater than the intake valve clearance.** While clearances do vary by engine model, for any given auxiliary diesel engine, the design principle is universal: the exhaust components expand more due to heat. Therefore, the required cold exhaust clearance must *definitely* be **greater** than the intake clearance, not possibly less than.