When an automobile engine emits clanking metal noises while driving, how should we address such an issue?
1. Causes
- Low octane rating
- Excessive carbon buildup or sludge inside cylinders
- Severe cylinder wall wear
- Cooling system issues
- Coolant leakage or low coolant level
- Engine oil leaks or high oil consumption
- High-speed or overload operation causing excessive temperatures
- Excessive clearance between piston pin and cylinder liner
- Impurities in engine oil leading to poor lubrication
- Poor lubrication between piston and cylinder
2. Specific Reasons
- Assembly Errors:
- Installing piston upside down during assembly; excessive clearance between piston and cylinder beyond standard limits; improper repairs causing large clearance between piston and cylinder, or severe cylinder wear resulting in excessive clearance. During cold engine operation, large piston clearance leads to pronounced knocking noises, which diminish or disappear as engine temperature rises and piston expands, reducing clearance.
- Adverse Working Environment, Abnormal Components:
- Low oil pressure or inadequate oil viscosity failing to meet operational requirements, causing poor engine lubrication and potentially leading to direct piston-cylinder contact or high temperatures deforming pistons.
- Rod deformation, excessively tight fit between connecting rod bearings or piston pins causing impact noises against cylinder walls during piston movement.
- Indirect Causes Such as Unstable Combustion:
- Rapid combustion of combustible mixture causing excessive pressure inside cylinders, resulting in piston skirt impacting cylinder walls and producing knocking noises.
- Appearance of detonation phenomenon with sudden temperature and pressure rise, forming pressure waves impacting cylinder walls.
3. Diagnosing Knocking Phenomenon
Method One: Auscultation Method Place the vehicle on a level surface, start the engine and warm it up to normal operating temperature. Press the accelerator pedal to increase engine speed to 2500 rpm and then release it. When the speed drops to 1500 rpm, if continuous tapping sounds are heard from the cylinder, it can be preliminarily diagnosed as a knocking phenomenon.
Method Two: Vibration Sensing Method By touching the engine block, sense for any abnormal vibrations. Knocking phenomena usually accompany noticeable vibrations, especially at high engine speeds.
Method Three: Engine Oil Pressure Testing Method Check if the engine oil pressure is normal. If the oil pressure is too low, it may be due to excessive crankshaft bearing clearance causing knocking. Use a professional oil pressure gauge for accurate testing to ensure reliable results.
4. Resolving Knocking Faults
Solution One: Replace Worn Parts If knocking is caused by wear of pistons, piston rings, or cylinder walls, replace the corresponding worn parts and perform necessary adjustments and tightening.
Solution Two: Adjust Clearances Inspect and adjust crankshaft and connecting rod bearing clearances to ensure they are within normal ranges. If clearances are excessive, replace bearings promptly.
Solution Three: Improve Lubrication Conditions Regularly change high-quality engine oil to maintain lubrication performance. Additionally, check the working condition of the oil pump to ensure oil pressure remains within normal range.
Conclusion
While engine knocking is common, proper diagnosis methods and solutions can effectively address the issue. Using auscultation, vibration sensing, and engine oil pressure testing methods allows for quick and accurate identification of knocking phenomena. By replacing worn parts, adjusting clearances, and improving lubrication conditions, engine knocking issues can be completely resolved, ensuring normal engine operation.
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