Engine Bearing – Function, Failure Symptoms, Causes And Prevention

Engine Bearing - Function, Failure Symptoms, Causes And Prevention
Engine Bearing - Function, Failure Symptoms, Causes And Prevention

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

However, failure of an engine bearing commonly leads to; serious reconditioning work of the engine.

Most often, including its disassembly; regrinding of the crankshaft and replacing the engine bearing.

As long as there’s a steady flow of clean oil; an engine bearing will generally last a long time. But, if the oil’s dirty or if the supply is cut off; that’s when the problems start. That’s why, bearing lubrication is so critical. 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.

Sometimes, failures are the result of simple installation errors.

How Engine Bearings Work

Engine Bearing Oiling Illustration
Engine Bearing Oiling Illustration
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.

This oil wedge lifts the shaft off the bearing surface and supports it during engine operations. Consequently, under normal operating conditions and a continuous supply of clean oil; the shaft and bearing surfaces will remain separated.

The properties required for bearing materials:

  • Fatigue strength (load capacity)
  • Seizure resistance (compatibility)
  • Wear resistance
  • Conformability
  • Embeddability
  • Corrosion resistance
  • Cavitation resistance

The Common Engine Bearings Used In Engines Are:

Main Bearings

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 consists of two parts. An upper and lower. The upper part of a main bearing, commonly has an oil groove on the inner surface.

The lower of a main bearing has a hole for passing oil; to the feed holes in the crankshaft. Finally, some main bearings may have thrust bearing elements; supporting axial loads and prevent movements along the crankshaft axis.

Connecting Rod Bearings

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

Con-rod Bushings

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

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 incorrect 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; improperly put into a position where the hole is needed.
  • When a connecting rod or main bearing cap is; installed in the wrong position.
  • If a bearing isn’t set into place securely; lubrication will be insufficient and cause failure.

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; affecting the connecting rod and/or main bearings.
  • Excessive loads, can similarly affect the bearings.


So, 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 examination may reveal some scoring, wiping, dirt or; other debris embedded in the surface of the bearings.

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

Thank You !