
4 Engine lubrication
4.1 FRICTION AND WEAR
Basic considerations
The main factors that can reduce the performance and
life expectancy of the engine and other parts of the
motor vehicle are the closely related phenomena of
friction and wear.
Friction can be described as the resistance that a
material develops against sliding contact. When an
apparently smooth surface is viewed through a powerful
microscope, innumerable tiny projections and depres-
sions are seen; these are termed surface asperities. They
may be likened to a mountain chain, so that when two
surfaces are rubbed together their action is analogous
to that of two mountain chains slidin ...