🔍 Key Concepts

• Diesel main bearing failure modes and what each one looks like on the bearing surface • The function of the lube oil filtration system and what happens when it is ineffective • How overheating, water contamination, and excessive bearing pressure typically appear on bearings

💭 Think About

• Which of the listed problems would most logically cause dirt to become embedded into the soft bearing material and cause scratches on the journal? • Think about what you would expect to see if a bearing were overheated – would that mainly cause discoloration, surface melting, or embedded particles? • If water were present in the oil, what signs would you expect – and would that directly lead to impregnated dirt in the bearing surface?

✅ Before You Answer

• Match the described symptoms (impregnated dirt + scratches) with the most characteristic cause, not just a possible cause • Eliminate options that would more likely show heat discoloration, wiping, or metal deformation instead of embedded foreign material • Consider what condition would allow solid contaminants to remain in circulation in the lubrication system and reach the bearing surface