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Diesel engines are designed to withstand years of tough labor, but only if they are built correctly from the start. Many diesel engine failures are caused by a lack of knowledge during the remanufacturing process. Still, when something goes badly wrong, it can be almost impossible to uncover what caused the failure in the first place.

In most cases, people think of a catastrophic lower-engine failure as a connecting rod punching a hole through the side of the block. It’s dramatic, it’s loud, and the cause is usually down to being too enthusiastic with the throttle or boosting the engine performance well beyond its designed tolerances. The diagnosis is simple.

But what about the quiet killers? The failures that happen while you’re just cruising down the highway, where everything seemed fine until the smoke started rolling out of the dipstick tube? These are the problems that haunt shop owners and enthusiasts alike.

Let's look at the details behind these issues and discuss what can affect rotating assembly failures centered around thrust bearings.

What Does a Thrust Bearing Actually Do?

In simple terms, a thrust bearing prevents the crankshaft from sliding front-to-rear; this is called an axial load. It absorbs the force applied when you engage a high-performance clutch or when a torque converter creates pressure against the crank. It is not the same as the main bearings that support the crankshaft's rotation, which carry a radial load.

With an out-of-spec thrust bearing, excessive end play can occur, which is a leading cause of recurring rear main seal leaks and eventual engine failure.

Thrust Bearing Failure: The Engine Killer

Bearing failures can be caused by several factors, ranging from insufficient lubrication and oil contamination to inadequate cooling. And while there are many types of bearing issues, thrust bearing failure is arguably the most dreaded. That’s because the thrust bearing’s primary job is to control the crankshaft’s movement, and when it fails, the crank can move forward or backward within the block.

This can cause serious damage to the engine’s internals, destroying main bearings and scoring pistons and cylinders. While different engines use thrust bearings with varying specifications, they can all fail if they are not installed correctly or are stressed beyond their design limits. The thrust bearing is a small part with a huge job, constantly fighting friction and pressure.

Failures are often difficult to pinpoint because they can be caused by a variety of external factors:

• Transmission Issues: A ballooning torque converter or high line pressures in a triple-disc setup can force the crank forward.
• Clutch Abuse: Riding the clutch on certain trucks can transfer a lot of load to the bearings.
• Installation Errors: If a builder doesn't pre-load the axial thrust before torquing the main caps, the bearing won't seat correctly.
• External Factors: Believe it or not, even oversized 40-inch tires or poor electrical grounding (which can cause arcing at the crank) can wipe out a thrust bearing.

These failures can occur without much notice, so prevention is always better than a cure. Read on to learn what factors you can address to minimize the likelihood of the thrust bearings failing.

Measuring Clearances: Builder vs. Assembler

You cannot simply trust that a new part is good just because it’s new. Manufacturing defects occur regularly, so it's important to qualify every new part installed in an engine. For example, on a thrust bearing, the crush factor - the small amount of bearing material that overhangs the housing to keep it locked in place - must be verified. A typical thrust bearing has about a 0.002" tolerance range for its crush dimension. Too little crush means the bearing can spin or walk. Too much crush can cause the bearing to distort, overheat, and then fail.

The thrust bearing directly affects end play. End play refers to the distance the crankshaft is allowed to slide forward or rearward when installed. The distance between the thrust faces is critical. A brand new thrust bearing can be out of spec, and will cause damage if installed:

• The Danger Zone: If the faces are too far apart, the clearance between each face and the crankshaft journal will be too tight, and oil will not get between each thrust face and the journal. If the faces are too close together, the crankshaft end play will be excessive. You’ll end up with persistent rear main seal leaks and eventual failure. If clearance is off by even a few thousandths, it’s a mistake that costs thousands of dollars to repair.
• Target End Play: Most diesel engines require a very specific amount of end play. For example, on the 6.0 Power Stroke, the end play spec is 0.004"-0.008". There is not much margin for error.

We've just walked through two critical dimensions on one bearing, and if the bearing is out of spec by a few thousandths, expensive problems can result. When rebuilding an engine, many parts must be qualified before installation.

One of the most critical takeaways for any diesel enthusiast is the difference between an engine assembler and an engine builder. An assembler simply takes parts out of a box and puts them together. Engine builders, like our team at Choate Performance, measure and inspect every part.

Crankshaft Issues: The Windshield Wiper Effect

Even if your clearances are perfect, your crankshaft might still be working against you. This is a phenomenon known as the 'windshield wiper effect.' This happens when the surface finish of the crankshaft thrust face has a starburst or sunburst pattern. And that comes down to improper crank grinding and not having the right tools for the job.

As the crank spins, these microscopic marks act like tiny wipers, literally flinging the oil away from the bearing surface. Without that oil film, you get metal-on-metal contact.

• Surface Roughness (RA): Professional shops use a profilometer to measure the average roughness of the metal.
• Polishing Direction: A crankshaft must be polished in a specific direction (favorable rotation) to ensure the microscopic metal 'hairs' lie down rather than standing up, which would remove oil from the bearings.

Why Quality Control Matters

Whether you're running a 6.7 Powerstroke, a Duramax, or a 5.9 Cummins, your engine is a massive investment. At Choate Performance, we don't just slap it together. We use custom-machined tools to verify every spec because 'it looks okay' isn't a measurement. We offer turnkey engines for every need:

• Short Blocks: Ideal for budget-friendly builds requiring a proven, reinforced foundation.
• Long Blocks: Fully assembled with heads, cam, and valve train for a quicker, seamless install.
• Full Running Engines: Complete drop-in solutions that are tested and ready to get to work.
• Upgraded Internals: Upgraded pistons and internal components meticulously designed to handle added horsepower and torque safely.

If you’ve suffered a repeat failure or are looking for a build that has been qualified to the nth degree, reach out to us. Our engines are fully remanufactured and re-engineered to outperform factory designs. Every detail is inspected, machined, and upgraded to meet or exceed OEM specifications.

Our reman process corrects the known weak points in Ford Power Stroke, GM/Chevy Duramax, and Dodge Ram Cummins engines. We’ve seen the horror stories, and we’ve built the solutions to ensure your diesel stays on the road, not on the shoulder.