Question 132Motor Plants - Assistant Engineer

The correct answer is C) hydraulic "push rods". In modern, large, low-speed main propulsion diesel engines, the opening of the exhaust valves is typically actuated by hydraulic "push rods" rather than direct action of the overhead camshaft, compressed air pressure, or direct action of the main piston moving down. Hydraulic "push rods" provide a more precise and reliable method of valve actuation compared to the other options, which may not be suitable for the demands of a large, low-speed diesel engine. The other answer choices are incorrect because: A) direct action of the overhead camshaft is more common in smaller, high-speed diesel engines; B) compressed air pressure is typically used for engine starting, not valve actuation; and D) direct action of the main piston moving down would not provide the precise control required for proper valve timing and opening.