Engine Bearing – How They Actually Work – Failure Warning Signs

Engine Bearing - How They Actually Work - Failure Warning Signs
Engine Bearing - How They Actually Work - Failure Warning Signs

An engine bearing is a small and relatively inexpensive component, of an internal combustion engines.

However, failure of an engine bearing most often leads to, serious reconditioning work of the engine.

Most often, including its disassembly, regrinding of the crankshaft and replacing the engine bearings. And, that’s only, if it was caught in time.

So, as long as there’s a steady flow of clean oil, an engine bearing will usually last a long time.

But, if the oil’s dirty or if the supply is cut off, that’s when the problems start. And, that’s why, bearing lubrication is so critical. Subsequently, from the second the engine turns over, until it is shut down. Also, identifying the root cause of a bearing failure, is crucial in preventing a repeat failure.

However, failures can also be, the result of simple installation errors.

How Engine Bearings Actually Work

Anti-friction Components
Anti-friction Components
Engine Bearing Oil Film Illustration
Engine Bearing Oil Film Illustration

Though there is not much to an engine bearing at first glance, it is a true marvel of engineering. All bearings depend on a film of oil, to keep shafts and bearing surfaces separated:

  • At rest, the shaft and bearing, are always in contact.
  • On startup, the shaft, contacts the bearing briefly.
  • Running, the shaft pulls oil from the clearance space, into the wedge shaped area, between the shaft and bearing.

So, this oil wedge, lifts the shaft off the bearing surface and supports it, during engine operations. As a result, the shaft and bearing surfaces, will remain separated. But, only under normal operating conditions and a constant supply of clean oil.

The properties required for bearing materials:

  • Fatigue strength.
  • Seizure resistance.
  • Wear resistance.
  • Conformability.
  • Embeddability.
  • Corrosion resistance.
  • Cavitation resistance.

The Most Common Bearings, Used In Engines Are:

Common Main Bearings

Main Bearings
Main Bearings

So, most engines have, at least two main bearings. One at each end of the crankshaft. Main bearings, support the crankshaft, in the engine block. A main bearing has of two parts. An upper half and lower half. So, the upper half of a main bearing, commonly has an oil groove, on the inner surface.

The lower half of a main bearing, has a hole for passing oil, to the feed holes in the crankshaft. Furthermore, some main bearings may have, a built in thrust bearing. And, are used for supporting axial loads and prevent movements, along the crankshaft axis.

Common Thrust Bearings

Thrust Bearings
Thrust Bearings

In an engine block, crankshaft thrust bearings, are placed into grooves formed in the, engine block’s webbing. Their purpose is to, limit the crankshaft’s forward and backward movement. As a result, keeping the crankshaft, within a specific area of motion.

Common Connecting Rod Bearings

Connecting Rod Bearings
Connecting Rod Bearings

Connecting rod bearings, are mounted in the, big end of the connecting rod. A bearing has two parts, (commonly interchangeable). Rod bearings, provide rotating motion of the crank pin, within the connecting rod.

Common Piston Pin Bushings

Piston Pin Bushings
Piston Pin Bushings

Small end bushings, provide relative motion of the piston. Relatively to the connecting rod, joined to the piston.

Common Camshaft Bearings

Camshaft Bearings
Camshaft Bearings

Camshaft bearings, support the camshaft in the engine and allow for its rotation.

So, proper selection of bearings, will go a long way, toward a successful engine rebuild.

Furthermore, it is a good idea to inspect your old bearings, before starting any new rebuild or repair. Because, they do tell a story and will help find, the original problem.

Worn Engine Bearings
Worn Engine Bearings

So, identifying the root cause of a bearing failure, is crucial in preventing, the recurrence of the failure. A simple replacement of the bearings, will not address the factors, that led up to the failure. It is important to note, that in many cases, the premature bearing failure, is due to a combination of causes. One common cause, is the wrong bearing clearance. So, if you do not find the original cause, bearing failure can repeat itself.

Failure Symptoms Causes And Prevention

Because bearing manufacturers do such a great job in making bearings, they will always have the best information. We will let them speak for themselves. As their engineers, have all the information you will need. So, here is a list of the common ones we have found.

The following notes and illustrations, will assist you in the diagnosis and causes, of bearing failures:

Clevite  Engine Bearings

Clevite 77  Bearing Failure

King  Engine Bearings

Mahle  Engine Bearings

Engine bearing failure, can also occur, as a result of, faulty machining or careless assembly.


Sometimes, failures are the result of, simple installation errors:

  • If a bearing half, without an oil hole, is wrongly put into a position, where the hole is needed.
  • When a connecting rod or main bearing cap, is put in the wrong position.
  • If a bearing isn’t set into place securely, lubrication will be insufficient and cause failure.
Worn Crankshaft Connecting Rod Journal
Worn Crankshaft Connecting Rod Journal

Other causes of bearing failure:

  • Excessive idling, can result in an oil film, that can not support the load needed.
  • Engine lugging, can distort the crankcase and/or crankshaft. Also, the connecting rod and/or main bearings.
  • Excessive loads, can also affect the bearings.


Consequently, your old engine bearings, can reveal a great deal about your engine. As well as, conditions that may have contributed to their failure. All bearings, will show some degree of wear. But, a close check may reveal some scoring, wiping, dirt or other debris embedded, in the bearing surface.

So, use the links above, to compare your old bearings, to the ones in the pictures. Because, that information may lead you to, why the original bearings failed. Finally, saving you time and money.

Thank You !