Combustion 101

To solve the problem of friction in an engine, a
lubricant is used…motor oil.  Several quarts of
motor oil reside in a pan attached to the bottom of
the engine block, usually covering the crankshaft as
well.  The oil in the pan is pumped, by an engine-
driven pump, to the top of the engine through small
passages inside the engine block.  Oil is also
pumped directly to the surfaces of the rotating
parts, directly into the bearings.  

The soda can needs a bearing upon which to spin
smoothly and easily, it needs the plastic cup.  
Now lets imagine an improvement over the basic
slippery bearing, lets add lubrication.  Going back to
the example of a soda can spinning in a plain plastic
cup, lets add several drops of oil to the inside wall
of the plastic cup.  If we now spin the can, it spins
even smoother and easier.  A lubricated bearing
does an even better job than just a plain bearing.  
In fact the oil is now the bearing.  The oil creates a
thin film between the side of the soda can and the
inside wall of the plastic cup.  The soda can now
slides on this film of oil, and doesn't even touch the
inside of the plastic cup.  

Now what’s important is getting enough oil to
create a thorough film between the two rotating
surfaces.  We can drip oil into the cup and let the
can smear it all over, or we can cut small holes into
the side of the cup and squeeze oil into the cup
under pressure.  

Smooth metal surfaces with a thin film of oil,
sometimes under pressure-sometimes dripped, is
how most of the bearings inside an engine work.
Bearings are surfaces upon which
rotating parts slide.  Imagine a
soda can (or beer can if that’s
your pleasure) sitting inside of a
similarly sized plastic cup.  When
you spin the soda can, the side of
the can actually slides along the
plastic on the inside wall of the
cup.  The inside wall is the
bearing surface, as it facilitates
the sliding.  If you cover the
inside of the cup with say sand,
the soda can can’t spin easily and
the soda can’s surface will be
scratched by the abrasive sand.  
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