🔍 Key Concepts

• bearing lubrication and oil film formation in diesel engines • differences in loading direction and timing between four-stroke and two-stroke cycles • how reversing vs constant load affects oil wedge formation on journals

💭 Think About

• Think about what is happening to the crankshaft journal and main bearings during each stroke in a four-stroke engine versus each cycle in a two-stroke engine. • Ask yourself: does the direction of force on the crankpin and main bearings stay the same or change more often in a four-stroke engine? How might that help spread oil? • Which choice describes a fundamental mechanical difference between 2-stroke and 4-stroke operation, rather than something that depends on how a particular engine is equipped or on fuel type?

✅ Before You Answer

• Focus on the mechanics of the pressure direction on the journals, not on fuel grade or oil consumption. • Check which options describe design-dependent features (like specific lubricating systems) versus inherent cycle characteristics of 2-stroke vs 4-stroke engines. • Verify which situation would help maintain a more uniform oil film (oil wedge) around the entire bearing surface by changing the loaded area.