Main Bearings Failure Analysis

 So you're having a problem with the bearings in your diesel engine. But just what is causing this problem? Properly diagnosing the issue can help prevent it from becoming a recurring problem, so it's important to understand the full extent of the failure. 
This failure analysis can help you better understand what is causing the failure in your main bearing. Read on to see if you're having one of these problems.
Don't think it's your main bearings? Check out our rod bearing failure analysis!

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Bearing Failures Caused by Lack of Proper Lubrication

The picture below shows what happens when bearing fail from improper lubrication. Notice the extremely polished condition of the bearings with the worst streaking toward the center of the bearing. This is an indicator of oil starvation, possibly from a dry start up or low oil. 


Main Bearing Failure Oil Streaking | Highway & Heavy Parts

The following picture shows all of the main bearings laid out in the order they were removed. The red arrows point to bearings that experienced a catastrophic failure. The blue arrows show the number seven bearing set starting to fail. Note all the bearings show shiny rub spots that are a further indication of lack of lubrication.

Main Bearing Failure Points | Highway & Heavy Parts
Improper lubrication can cause failure in other parts of your engine as well. Read our article to see how a lack of lubrication can cause turbo failure in your diesel engine. 

Examples of Bearing Failures

There are many other diesel engine problems that can cause failure in your bearings. Check out the pictures below to see what might be giving you trouble.

The picture below shows a wear pattern caused by an uneven and rough cam bearing bore in the block. 

Main Bearing Failure Wear Pattern | Highway & Heavy Parts

In the image below, you can see that foreign material was trapped between the main bearing and the block.

Main Bearing Failure Foreign Material | Highway & Heavy Parts

The next picture provides an example of uneven wear caused by bore distortion:

Main Bearing Failure Uneven Wear | Highway & Heavy Parts

Below is a picture of uneven wear caused by a bent connecting rod:
Main Bearing Failure Uneven Wear Connecting Rod | Highway & Heavy Parts
Next, we see uneven wear caused by severely worn crankshaft rod journals:

Main Bearing Failure Uneven Wear Crankshaft | Highway & Heavy Parts

Additionally, you can have a bearing fail from improper assembly. Below is an example of a bearing failure caused by assembly error; the oil feed hole in the connecting rod was not lined up with the bearing lubrication hole.

Main Bearing Failure Assembly Error | Highway & Heavy Parts

As you can see, diesel engine bearing failure can be caused by many different issues. Several of them can be due to a failure in a separate component. That's why it's so important to identify the cause of the failure. 


If you have a problem with your diesel engine bearings or components, let Highway & Heavy Parts help! We have ASE Certified Technicians on staff ready to find you the parts you need. Call them at 844-304-7688, or request a quote online!

Originally Posted November 18, 2015; Edited March 30, 2020