1. Plain bearings (also called journal bearings or sleeve bearings): These are cylindrical bearings made of a softer material (like babbitt, copper-lead, or aluminum) that conforms to the rotating shaft. They rely on a thin film of oil for lubrication.
2. Rolling-element bearings (also called anti-friction bearings): These bearings use rolling elements (balls or rollers) to reduce friction between rotating and stationary parts. Examples include ball bearings, roller bearings, and needle bearings. While less common in *main* engine components (like crankshaft bearings), they're frequently used in other engine parts like camshafts, accessory drives, and valve trains.
