Engine Bearing – Function – Failure Symptoms – Causes And Prevention

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

Engine bearings are small and relatively inexpensive components of all 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, the bearings will generally keep moving along fine. If the oil’s dirty, though, or if the supply is cut off, that’s when the problems start. Bearing lubrication is critical from the second the engine turns over until it is shut down. If not engine bearing failure will result costing you major repairs or possibly a new engine. So, identifying the root cause of a bearing failure is crucial in preventing the recurrence of the 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 engine 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 engine 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

Crankshaft main bearings support the crankshaft in the engine block. A main bearing consists of two parts: upper and lower. The upper part of a main bearing commonly has an oil groove on the inner surface. 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

Rod bearings provide rotating motion of the crank pin within the connecting rod. A bearing consists of two parts (commonly interchangeable).

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 camshaft and provide its rotation.

So, proper selection of bearings will go a long way toward a successful engine rebuild. It is a good idea to inspect your old bearings before starting any new rebuild or repair. They do tell a story and will help find the problem before just replacing parts.

Worn Engine Bearings Displayed On Table
Worn Engine Bearings Displayed On Table

Identifying the root cause of a bearing failure is crucial in preventing the recurrence of the failure. A simple replacement of the bearings typically 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. Also, a common issue is incorrect bearing clearance. Finally, if you do not find the original cause engine bearing failure damage will repeat itself.

Failure Symptoms – Causes And Prevention

Because bearing manufacturers do such a great job on 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 courtesy of:

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.

Double Check Crankshaft
Double Check Crankshaft

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 Engine 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 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.

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