🔍 Key Concepts

• Direct-reversing two-stroke diesel engines – how ahead/astern rotation is obtained • What must be changed so that fuel is injected at the correct time for the new direction of rotation • The role (or absence) of intake/exhaust valve cams in many large two-stroke crosshead engines

💭 Think About

• Ask yourself: on a direct-reversing two‑stroke, what component actually determines WHEN fuel is injected relative to crank angle? • Consider which item must be correctly positioned before starting air is admitted, so that the engine will not try to run in the wrong direction or misfire. • Think about which systems (fuel, valves, lube oil) are typically already running and which one must be mechanically shifted when changing direction.

✅ Before You Answer

• Identify which choice directly affects fuel timing relative to crank angle for ahead vs astern. • Verify which components in a large low‑speed two‑stroke are reversible mechanisms (can be shifted between ahead and astern settings). • Confirm that any action taken prior to starting air should enhance safe starting, not deprive bearings of needed lubrication.