Crankshaft bearings are essential elements of the crankshaft-piston mechanism located in the engine block and serve as sliding bearings for the crankshaft

Function of Crankshaft Bearings

The primary function of crankshaft bearings is to allow the crankshaft to rotate freely when the engine is running. Additionally, they must ensure the free flow of oil to the crankshaft’s main and connecting rod journals to create an oil film that reduces friction between moving parts and prevents wear.

There are two types of crankshaft bearings:

• Standard bearings: Ensure the free rotation of the crankshaft;
• Bearings with thrust washers: Hold the crankshaft in place, preventing excessive axial movement;

Each main journal of the crankshaft works with two crankshaft bearings, covering it from the top and bottom.

Almost every crankshaft bearing includes the following elements:

• A hole through which oil is supplied to the working surface;
• “Locks” – protrusions for the correct installation of the bearing in the crankshaft bed;
• A longitudinal (circumferential) groove for proper oil distribution;
• Thrust bearings also have special flanges that limit the axial movement of the crankshaft.

Typically, upper and lower bearings are not interchangeable. They differ in the presence (or absence) of holes and grooves, as well as in the anti-friction coating.

Every crankshaft bearing is made from a steel strip, the surface of which is coated with leaded bronze or another anti-friction material based on tin or lead. These anti-friction coatings reduce friction and ensure a long service life for the parts. Crankshaft bearings are replaceable engine parts that can be purchased as sets – for the entire engine – or individually, as pairs for each journal.

As the crankshaft journals and the bearings themselves wear out, the gap between the bearings and journals inevitably increases, oil pressure in the lubrication system drops, and the engine starts to produce extraneous noise – a knock. This is a critical sign that the bearings need to be replaced.