Diagnosis And Troubleshooting Of Automobile Crankshaft Bearing Noise Faults

cause of issue

  1. The crankshaft bearing and crankshaft journal are worn, causing the matching gap between the two to become larger and causing a knocking sound.

  2. The fastening bolts of the crankshaft bearing are loose.

3. Poor lubrication of the crankshaft bearing causes the alloy to burn or fall off.
4. The axial clearance of the crankshaft is too large, causing the crankshaft to move forward and backward, causing the axial positioning end surface of the crankshaft and the thrust washer to collide with each other, causing noise.  5. The crankshaft is bent or broken, and produces impact sounds during operation.
5. The flywheel fastening bolts are loose.

Troubleshooting and troubleshooting

  1. Remove the engine oil filler cap, put your ear close to the oil filler and listen, and at the same time repeatedly change the engine speed for testing. When the engine speed suddenly changes, a dull and continuous “thumping” metal knocking sound will be emitted. In severe cases, the engine will vibrate greatly, indicating that the crankshaft bearing is making noise.

 2. Use the single-cylinder fire-off method to test, and the sound does not change. Then use the fire-off test in two adjacent cylinders.

If the sound weakens significantly after a certain two cylinders are cut off, it means that the crankshaft bearing between the two cylinders is noisy.

  3. If the engine is run at high speed, the body will vibrate greatly, and the oil pressure will drop significantly. This indicates that the crankshaft bearing clearance is too large or the bearing alloy layer has fallen off.

 4. Drain all the engine oil and remove the oil pan for inspection.

 (1) If there are bearing alloy particles in the engine oil or on the oil pan wall, it means that the crankshaft bearing alloy has fallen off, and new bearings of the same grade should be replaced.

 (2) Check whether the crankshaft bearing cover bolts are loose. If they are loose, tighten them to the specified torque.

 (3) Check whether the bearing clearance is too large by checking the crankshaft bearing clearance. If it is too large, replace it with a new bearing of the same grade.

 5. When the clutch pedal is depressed, the sound weakens or disappears. Use a pry bar to dislodge the flywheel or crank arm. If the axial movement is too large, the thrust bearing should be replaced.

 6. As the engine temperature increases (the oil viscosity becomes lower), the noise increases significantly. When the engine speed reaches high speed, the noise appears chaotic, indicating that the crankshaft is bent and should be removed and straightened (or replaced).

7. If the sound occurs at the rear of the engine, and there is a banging sound at the moment when the engine speed suddenly increases or decreases, it means that the flywheel fastening bolts are loose and should be tightened to the specified torque.