Combustion 101
The Camshaft

Wait a second- I didn’t mention what
moved the intake and exhaust valves.  
That's important, so here goes.  The valves
are opened and closed by the lobes of a
camshaft.    A cam is a bump on a rotating
wheel or shaft that strikes a lever.  A cam
lobe is simplistically an egg shape that
rotates and pushes on a lever with the
smaller pointy end once every complete
turn.  A camshaft is a series of cam lobes
placed next to each other-like the steps of a
circular staircase.
The Mechanics
The Timing
The Mechanics
The Timing
Each lobe on the camshaft pushes a lever (called a
rocker arm) which opens one of the valves of the
cylinder.  One lobe is for the intake valve and one is
for the exhaust valve of the cylinder.  For each
additional cylinder, there are additional cam lobes to
open those additional valves.  The cam opens its
valve once every time it rotates and the position of
the cam within the rotation of the camshaft is what
determines when the valve opens.
Camshaft diagram
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