What are the classifications of engine abnormal noises?

[Ellis]

Classifications of engine abnormal noises: 1. Loose fasteners: Vibration during engine operation causes certain components to loosen, resulting in impact sounds. For example, abnormal noises caused by loose flywheel fixing bolts or loose connecting rod bolts; 2. Deformation or damage of individual components: Abnormal noises caused by deformation or damage of certain parts. For example, knocking sounds due to bent connecting rods, broken valve springs, or fractured crankshafts; 3. Improper assembly, adjustment, or repair: Abnormal noises caused by incorrect assembly, adjustment, or repair leading to improper component clearance. For example, noises due to overly tight piston pin assembly or improper valve clearance adjustment; 4. Excessive clearance: Natural wear of certain moving parts in the engine leads to increased clearance beyond the acceptable range, causing abnormal noises, such as knocking sounds between pistons and cylinder walls or impact sounds between connecting rod bearings and journals; 5. Poor lubrication: High-quality lubricating oil and appropriate pressure can create a good lubricating oil film. The thicker the oil film, the less mechanical impact, reducing the likelihood of abnormal noises. If the oil film is too thin, accelerated wear occurs, resulting in obvious and clear abnormal noises; 6. Abnormal combustion: In gasoline engines, ignition timing that is too early or too late causes detonation. In diesel engines, overly early fuel injection timing leads to premature and rough combustion, producing metallic knocking sounds.