Connecting rod bearings

What is it ?

Connecting rod bearings provide rotating motion of the crank pin within the connecting rod, which transmits cycling loads applied to the piston. Connecting rod bearings are mounted in the Big end of the connecting rod.
 

What are the symptoms of a bad connecting rod bearing ?

Knocking Noise from Engine
Listen for a knocking noise when the engine is running. This will likely be worse when the engine is cold and before the oil has had a chance to warm up and begin thoroughly lubricating the components. A rod knock is a hollow sound that speeds up as the engine RPMs rise. The knock may still be there when the car is warm or may go away entirely.

Low Oil Pressure
Check the oil pressure. A bad rod or rod bearing can also cause the oil pressure to be excessively low. Signs of low oil pressure can be an oil pressure light turning on or a low oil pressure reading if the engine has an oil pressure gauge.

Excessive Oil Consumption
Determine if the engine is using excessive oil. If the engine is consistently running low on oil, it may be due to a bad connecting rod or bad connecting rod bearing.

How can we diagnosis the connecting rod bearing ?

Plug Wire Removal

1. One way to identify the cylinder connected with the faulty rod bearing is to open the car hood and pull out all spark plug wires one by one.
2. After removing each wire, turn on the engine and check if the knocking sound still persists.
3. If the sound is eliminated, this means that the cylinder from where the plug wire was just removed has a faulty bearing on its connecting rod.

Visual Inspection

1. One can visually inspect the bearings to see if they are damaged or excessively worn-out, without removing parts of the engine.
2. First, raise the front wheels with a jack, and get under the engine, after setting the parking brake.
3. Then, remove the long drainage bolt from the oil pan with a wrench, to drain off its oil. Make sure to keep a catch pan underneath to prevent spills.
4. If the oil contains metal shavings, then it is a warning sign of bearing failure.
5. Finally, remove the oil pan by loosening the bolts surrounding it.
6. Remove and inspect the bearings for any damage.
7. If rather than a smooth wear all over, the bearings show scratches, dirt buildup, discoloration, or pitted surfaces, then they need to be replaced.