Evening capital news. (Boise, Idaho) 1901-1927, 1919-04-20
A chain is no stronger than its
weakest link, the ignition system is

IF A chain is no stronger than its
weakest link, the ignition system is
certainly no stronger than its spark
plugs. The ignition system may be
functioning perfectly in every other
particular, but If its spark plugs are
! not transmitting proper sparks to the
combustion chamber, the entire SIS
tenn is deranged.
| The spark plug is simply the means
of getting the flame or spark into the
combustion chamber. This is srcoIn-
Plished by means of a gap between
the ends of two wires. The electric
spark jumps this gap and thus mo-
mentarily passes through the fuel
charge in the combustion chamber, fir
ing 1t. In addition to affording the
means of exploding the, fuel charge,
the spark plug must resist the tremen-
dous forces within the chamber when
the explosion takes place and must not
permit gas to escape through 1t. Con
sidering that each plug in the -ngine
must deliver hundreds of thousands
of sparks in the course of days run,
while being subjected all the time to
extremely high heat and explosive
pressures, the wonder is that they give
the service that they do.
There are a great many different
designs of spark plugs on the market
today and many different materials
are employed in making them. l will
describe the different types briefly and
explain the care that should be given
them by the car owner, IL he hopes to
get maximum efficiency from them.
AS noted above, the spark is intro
duced into the combustion chamber by
means of a gap, across which the cleo
trio current jumps. To accomplish this
there must be two wires, which are
also known as electrodes. One of
these wires, the one which brings the
current from the magnetic or other
| current source, must be insulated so
that none of the current will leak away.
! The other wire, which receives the
current after it jumps the gap, must be
grounded. This is done by attaching
the wire to the spark plug shell, which
Is of metal and screws into the metal
cylinder. The insulated electrode is
embedded in porcelain, mica or stone
, of some sort.
The shell and the interior of the
| plug must be Joined so tightly that
no gas can escape and this is usually
done by means of IA gasket, after the
two have been cemented together or
compressed together by means of a
nut
Spark plugs may be divided into two
distinct groups according to whether
I they have open or closed ends. Not
all engines will operate properly with
both types. Some require an open end
plug, While others need a closed end
unit. Car owners should note this fact
in buying this equipment.
| The vital parts of the spark plug
are the electrode and the insulating
unit. The insulator is made, as l men
toned, of porcelain, mica, stone or
some similar substance designed to
resist high temperatures and changes
of temperature without cracking.
Porcelain and stone are more Xix ely to
crack than is mica, and for this reason
some plug makers combine an outer
insulator of stone, with an inner core
of mica. The one failing that mica
! his is q tendency to absorb oil, but
| in one plug of popular make the mica
| is literally wound, which seems to be
about the only way of overcoming the
troubles with this substance. The
stone and mica plug seems to fill the
requirements for a good plug. which
cannot possibly be fulfilled by an or
binary plug. If the outer insulator
! should break in a combination plug,
service goes on Just as efficiently be-
cause the inner core is unaffected. \
most important consideration in con-
nection with this plug is that the outer
insulator may quickly and easily be
! replaced. The construction also af-
fords absolute protection against COM
preston leakage.
| The average car owner cannot hope
| to tell by looking at a spark plug whe-
Their the materials used are good, bad
or Indifferent. For this reason it is
important to buy plugs made by re-
sponsible manufacturer with a repu-
tation to live up to.
| The electrodes, which carry the
spark, are obviously subjected to high
temperatures, and the materials used
| in them must be calculated to with
stand this service. Nickel steel wire
is commonly used, but in buying plugs
it is well to see that the electrodes are
thick and heavy. as naturally these
last longer than smaller ones would
! Undoubtedly the most frequently en-
countered spark plug trouble is crack
ed insulators, which allow the current
| to leak away. Cracks in the insulator
may develop through faulty material,
through carelessnesS in handling