🔍 Key Concepts

• Crankcase pressure – what it is and what normally causes it to rise in a large diesel engine • Difference between problems in the combustion space (liners, rings, relief valves) and problems in the lubrication or scavenge air systems • How blow‑by from the cylinder into the crankcase can occur

💭 Think About

• For each choice, ask yourself: Would this fault allow combustion gases to leak down into the crankcase, or does it mainly affect some other part of the system? • Think about whether lube oil pressure or scavenge air pressure is normally sealed off from the crankcase, and how a change there would (or would not) change crankcase pressure. • Consider which component’s wear or failure would increase the path for gas leakage past the piston into the crankcase.

✅ Before You Answer

• Identify which option is most directly connected with blow‑by of gases past the piston into the crankcase. • Eliminate any options that mainly affect safety venting of over‑pressure in the cylinder rather than creating pressure in the crankcase itself. • Verify which systems (lubrication, scavenge air, cylinder space) are normally separated from the crankcase by seals or rings.