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5 Potential Reasons Why Your Diesel Engine Camshaft Bearings Failed

May 10, 2021 Excavator blog

In your diesel engine, it’s not just the camshaft that can wear or fail. You also have to pay attention to the health of your camshaft bearings.

Bearing failure can cause extensive damage to other engine components, so it’s important to identify the root cause of issues and repair them as soon as possible. Below are some common camshaft bearing issues and possible causes to help you better identify what’s going wrong in your engine.


There can be several things that cause journal damage, including:


For proper function, bearings have to fit correctly, be aligned, and be supported. When that is not achieved, you can have damage to the bearing journal.

The below image shows a bearing whose measurements and wear marks indicate that the camshaft bearing bore in the block was probably oversized. The wear marks are uneven, indicating a likely distortion.

There was probably too much clearance space, which allowed the camshaft to move, hurting both lubrication and support.

The following bearing became blackened due to overheating caused by misalignment:


Not enough lubrication allows for increased friction, which in turn increases heat. The camshaft can then damage the bearing surface as it rotates, which, after further use, may eventually lead to a broken cam cap.

The image depicts the discoloration of a bearing journal because of poor lubrication. The blue arrows point to the extension of the issue onto the shaft.


If your bearings aren’t installed correctly, the lubrication may be negatively impacted. This can lead to bearing failure, as shown in the below image. Note the partially covered oil hole in the second image.

If the oil holes aren’t aligned correctly on install, the oil cannot properly lubricate the camshaft, again leading to increased friction and wear on the bearings. The image shows the improper alignment of the bearings leading to partially blocked oil holes.

Installing bearings the correct way can help prevent these problems. Read our past blog, Camshaft Bearing Facts and Installation, for tips on properly installing your bearings.


Too much wear can spell disaster for your camshaft bearings. Several things could be causing this, including:

  • Improper Install
  • Incorrect Bearing Sizes
  • Elevated Operating Temperatures

Again, with these issues we’d expect to see decreased lubrication, allowing for further damage to your bearings. If left long enough, you could experience total bearing failure.


Writing for the July-September 2018 issue of Engine Professional, Brandon Flannery points out that your engine must extremely clean before assembly. He finds that failed bearings are often caused by debris build-ups from poor cleaning and blowing with compressed air might only make matters worse.

Instead, rinse and wash them thoroughly to keep that debris from contaminating the oil that lubricates the camshaft and bearings. This dirt can either cause damage to the components’ surface, or block clearance space, both of which could lead to failure.

It’s also important to pay attention to specific cam types as you’re cleaning. The ISX Injector Camshafts, for example, are hollow, and sometimes debris collects inside the cam as it spins, like a centrifuge.

We have seen times when the cam is removed, the jarring from setting the cam on the ground causes the debris to break free. This debris can plug an oil hole, starving the bearing and ultimately failing the cam, bearing, and possibly the head.