The sun. [volume] (New York [N.Y.]) 1916-1920, 1919-03-16
THE SPARK Plug
AND WHAT 1T DOES
Expert Explains It's Uses and
Installation and Its
Proper Care.

The spark plug Is simply the means
OF introducing into the combustion
chamber of the engine a spark gap
formed between the ends of two wires
The spark jumps this gap, as 1t does 90
inparting It's heat TO the gas mixture,
thus exploding It. Simply stated, this is
the function OF the plug-to explode the
mixture by means OF the heat of a
spark, but at the same time the plug IT,
self must be able to Withstand the tre-
d. mendous heat and pressure inside the
cylinder; II must not allow escape of
. the gas mixture, II must unfailingly
transmit current so the gap will be
Jumped and II must do this many
thousands Of times mile OF running.
When one considers the work q spark
plug has to do. 1t Is surprising how well
and how long this little part remains In
service Plug trouble to-day is not so
common as it was years ago, and we
have heard of plugs functioning without
any attention for as many as 10000
miles
There are hundreds Of designs of
plugs made Of a variety of materials and
made in numerous shapes and styles. It
is easy to see how difficult It is to design
plug TO meet all the conditions de-
rnanded of 1t, yet the modern spark plug
does its work admirably we'll / wish to
of plugs, the way to install them prop
y erly. the type TO get and not to get.
plug troubles and how they may be rem
edied
Since the end OF the plug must IN
troduce gap into the combustion cham.
her there must he two wires or cleo
trodes with their ends separated TO form
the sap. One OF these electrodes which
takes the current from the cable or wire
ha =.
fectly insulated so no current will leak
out while the other electrode must be
grounded in some way. This latter
~ always IL attached to the spark hlua
~ shell or the metal part which screws into
the cylinder, while the other one, called
the centre electrode always is imbeddet
IN an insulator made OF porcelain. stone
mica, &c. Tho insulator and the shell
then must be Joined together to make q
unit OF the plug, and this is done either
by ccmenting them together. forcing
them TO compression tightness by means
Of A nut, &c. OF course the two part!
must so Mt together that no mixture
escapes. and the usual way OF obtaining
this tightness is by introducing a gaske
or two between the parts.
PluES are made with open or CLOSED
ends, but certain engines only will oper
ate successfully with each type. Otter
n ClOsSu Gnu pug tlNSS lIOuple WIN al
engine which operating with open enc
plug gives entire satisfaction.
Tho really important parts of the
spark plug are the insulator and cleo
trodes. The former is usually made o.
mica. or porcelain so Is to withstand
the tremendous heat and also change;
OF temperature without cracking. Por,
Celan and various stone composition!
are used, but OF course this type II
more easily cracked than mica, boil
by the heat and by a w1enc. when in
stalling. These materials may be uset
IN combination in the same plug, thu
best form consisting Of an outer ston'
insul7 Tor and an inner mica one. Thu
only trouble with mica in that it i
liable 10 absorb oil, hut II the con
struction is right this may he prevented
altogether. The one advantage OF tn,