Quote:
Originally Posted by Artan
Again. Why ball bearings in the wheel of the car under high presure of weight and sudden hits to pot holes do not require grease change whereas engines need oil change.
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Because (most) engines use what are called "plain" bearings, which rely on a very thin film of oil between two surfaces to allow the parts to slide past each other. This requires a very high quality of oil and periodic changes to maintain that quality. If the film of oil isn't maintained, the two parts will come into contact with each other and wear will result.
Wheels use ball or roller bearings in which two metal surfaces contact each other (one part rolls along the other, like a wheel rolling down a hill) and require far less lubrication to keep them working properly.