Main bearing

The number of main bearings is primarily determined by the overall load factor and maximum engine speed.

[1] Increasing the number of bearings in an engine will generally increase the size and cost of the engine, but also reduces bending stress and deflection caused by the distance from the crank pins to the nearest bearings.

[1] Some small single-cylinder engines have only one main bearing,[citation needed] in which case it must withstand the bending moment created by the offset distance from the connecting rod to the main bearing.

[2][3] The lower half of the main bearings are typically held in place by 'bearing caps' which are secured to the engine block using bolts.

The additional bolts result in increased strength, allowing the engine to withstand higher power output or RPM.