Johnson FCWR 304
Mechanism Description of an Autolite PV3 Spark Plug
Introduction. An Autolite PV3 spark plug is an automotive component used to ignite the fuelair mixture in the cylinder of an internal combustion engine. The spark plug starts the
combustion of gas by setting off a small spark at the appropriate time. This particular spark plug
is most often used in motorcycles. The spark plug is cylindrical with an overall length of 2 1/2
inches, a maximum diameter of 3/4 inch, and a weight of two ounces. The three main parts of the
spark plug are the main central conductor, the insulator, and the main body assembly.
Description of Parts. The central conductor is an electrical pathway for the positive current
flow. It is one piece of metal 2 1/2 inches long and 3/16 inch in diameter, cylindrically shaped
with a knob on one end. It is The central conductor runs down the center of the spark plug.
The insulator is an electrical nonconductor that prevents current flow from the central conductor
to the engine block. It is a 2 1/4-inch porcelain sheath with a maximum diameter of 1/2 inch. The
inside of the insulator is a hollow tube, 1/2 inch in diameter, through which the central
conductor, which it is baked onto, except at the very top and bottom.
The main body assembly is a multipurpose structure that is used as an electrical pathway for
negative current flow and for easy installation and anchoring of the spark plug. It has an irregular
cylindrical shape with a hollow tube 1/2 inch in diameter running down its center, onto which the
insulator is molded. The main body assembly is made of one piece of metal with a height of I
inch and a maximum diameter of 3/4 inch. The main body assembly is divided into three
subparts: the hexagon nut, the threads, and the electrode.
The hexagon nut provides a gripping surface for use in installation
and removal of the spark plug. It is located at the uppermost section
of the main body. It is a regular, six-sided polygon with a distance
of 3/4 inch between the opposite flat sections of the polygon. The
hexagon nut is constructed of the same metal as the main body and
is continuous with it. The hexagon nut is usually gripped by a
wrench when the spark plug is installed or removed.
The threads of the spark plug form a modified screw shaft to hold
the spark plug in the cylinder head of the engine. They are located
at the base of the main body and have a diameter of 1/2 inch and a
height of 1/2 inch. The grooves of the threads are cut in a helix
around the outside of the bottom section of the main body.
The electrode provides a pathway for the negative current flow. It
is L-shaped, with a width of 1/8 inch and length of 1/4 inch. The
electrode is located at the base of the threads and is constructed of
the same metal as the rest of the main body. A small gap of about
.025 to.030 inch is maintained between the electrode and the central
conductor. When current is delivered, the electricity will jump this
gap, causing a spark and igniting the fuel-air mixture.