To ensure driving safety, owners of Lada Niva 2121 vehicles should remain alert to abnormal noises from the engine’s main bearing area and promptly identify their causes. Below is a detailed analysis:
I. Methods to Diagnose Crankshaft Main Bearing Noise
The crankshaft main bearing plays a crucial role in the engine during vehicle operation: it protects the journal and bearing bore, reducing component wear caused by friction; additionally, it converts gas forces transmitted to the engine into torque through the piston connecting rod assembly, which is then output externally to drive the engine’s valve train and other auxiliary devices.
How to judge if the noise originates from the crankshaft main bearing?
Owners can first vary the engine speed repeatedly and listen for sounds at the oil filler port. If a low, dull thud is heard during sudden acceleration or deceleration, place a flat-blade screwdriver on the main crankshaft positions on both sides of the cylinder block to listen. If the low, dull noise remains distinct, the fault is likely related to the crankshaft main bearing.
II. Main Causes of Crankshaft Main Bearing Noise of Lada niva 2121
1. Loose Main Bearing
Run the engine at low speed and slightly oscillate the throttle. If the noise from the main bearing area increases with rising engine speed and becomes more pronounced when oscillating the throttle, the main bearing is likely loose.
2. Bent or Broken Crankshaft Main Bearing
If the noise is obvious at idle or low speed and becomes irregular at high speed, the main bearing may be bent or broken. Excessive engine vibration at high speed accompanied by a significant drop in oil pressure indicates potential bearing burnout or detachment of the anti-friction alloy on the main bearing, which also causes abnormal noise.
3. Severe Wear or Improper Selection of Main Bearing Shells and Journals
Severe wear between the main bearing shell (big end bearing) and journal, or improper selection of crankshaft main bearing shells leading to excessive fit clearance, can produce impact noise. If the noise occurs in the early stage of use or during normal operation, it is mostly due to loose main bearing cap bolts or blocked lubrication channels in the main journal. Conduct a fire cut-off test on two adjacent cylinders: if the noise decreases or disappears, the main bearing shell is the likely source.
4. Insufficient Torque of Main Bearing Cap Bolts
During installation, if the torque of the main bearing cap bolts does not meet the specified value, impact noise between the journal and main bearing shell may occur, resulting in abnormal sounds.
5. Poor Lubrication Due to Oil Issues
Insufficient lubricating oil in the crankcase or poor oil quality can cause inadequate lubrication, leading to burnout and detachment of the main bearing shell’s alloy, ultimately resulting in abnormal noise.
In summary, if abnormal noise is detected from the main bearing area while driving, stop the vehicle immediately, have it towed to a nearby repair shop, and inspect the engine bearings to eliminate faults promptly, ensuring safe driving.