Proper lubrication of the main bearings is more easily obtained in a single acting four- stroke/cycle diesel engine than in a single acting two-stroke/cycle diesel engine because __________.

Correct Answer: Option A — bearing pressure in a four-stroke/cycle single acting diesel engine is continually reversed

Four-stroke cycle engines continually reverse main bearing loads between upward inertia forces and downward combustion loads. This constant directional shift facilitates wedge-film lubrication, whereas two-stroke single-acting engines experience continuous unidirectional loads that hinder oil film formation.