The Washington times., 1929-02-13

lnefe are some parts oL inc
to remain inconspicuous no m
nor how important are the CHI
to time.
Such seems to be the lrrevocable
fate OF the spark plug-the unit
that passed out of the mind OF
motordom when it reached that
stage of perfection where 1t was no
longer necessary to stop every few
miles to clean and recondition the
plugs for the next few miles.
So far as the motor car owner is
concerned, the spark ping has be-
come the efficient emplcye that no
longer needs watching. Consequent'
ly. it is forgotten altogether. 1t
should not be overlooked.
Still Working On 1t
IL however, the individual motor
ist deIgns not to recognize the e&-
istence of this dutiful unit OF the
ignition system, the engineer can
not afford to do so. He has been
particularly busy with the spark
Mug of late. In his quest for
better performing engine, he Is go
ing to keep on working with IT,
Occasionally, reading the speclIl-
fications of a new model, the motor
enthusiast runs across the news tnat
it employs metric spark plugs. II
means about as much to him as
would the Port Said weather report
tor, the day after tomorrow.
liz however, the same LndlV:duai
were aware of the close kinship be-
tween the metric spark plug ana
the speed and power of his car,
characteristics in which he is deeply
interested, indifference might oe
transmitted into an intelligent in
terest. There is such kinshlp' II
is an exceedingly close one.
Different Type
There could not be, for instance.
any of these splendidly impressive
high compression engines OF today
without a spark plug as different
from it's predecessor as the engine
ia from the one it displaced. Great
ing this plug was no simple matter.
1t involved a huge research effort,
and in one case, before the fruits
of the research ripened, prom
inent plug maker was producing 70
different varieties to fit the de-
mands of the motor car industry.
In the first place, the high COM
preston engine demanded cool-
running plug. The higher the COM
preston, the cooler the plug must
be in operation. And yet, the plug
could not run too cool. When II
did. the engine did not run at all
after a brief interval OF giving
staggering service. This was De-
cause at a certain minimum operat-
ing temperature oil on the pug
turned carbon At the other ex-
treme, when the temperature was
too high. the condition of the plug
caused pre-ignition.
One evil is about as bad as the
other. Finding the happy medium
was no easy task. AS a matter OF
fact, the medium is NO sooner found
than the extremes show a disposi"
ton to change and a brand new
one has to be developed.
Conditions Faced
A list of some of the conditions
that make for great variation in
plug temperatures will give the lay
man an idea of what the plug de-
signer is up against when trying
to make a product that approx
mates omnipotence-whic it must.
Such a table, offered by one of the
leading engineers in the field, fol-
lows:
Engine speed, engine load, tenn
perature of the cooling water, tenn.
perature of the engine, fuel used
in the engine, the degree of spark
advance, the setting of the carbn-
rotor. the humidity, temperature of
the air around the plug, and the
draft around the exposed part of
the plug.
Quite an imposing list of vari-
ables. And when one considers how
each may vary between any two
of several million automobiles, one
of which may be racing green lights
in Spitzbergen in January while the
other is parked under the tropical
moon. there is no escaping. the fact
that the engineer is tackling a
sizeable problem.
What has happened chiefly in the
creation of the metric plug for to-
days engines is the reduction in
the area exposed to the tremendous
heat Of the engine. Precisely, Civ.
ing an average figure, the new plug
absorbs about two-fifths as much
heat as the older type. In the
modern high compression engine,
swooping down the country high
way at so miles an hour one of
the old plugs would be efficient for
Just a few minutes. After that it
would get too hot.
Not all car makers, of course,
have adopted the metric plug. Some
OF them have found it necessary
because of the less extreme change
in the compression ratios of the
engines they use. Others have
found as an acceptable substitute
not q plug that absorbs less heat,
but, instead, one that has larger
cooling surface.
Airplane Helped
In this respect. the plug has met
fate no different from that of
many another car feature. Seldom.
indeed, is< the reception of de.
velopment of any character unani-
nous.
Out OF all the changes that have
occurred, are occurring, and will
occur in respect to spark plugs, the
motorist will have to regard him.
self as indebted to the airplane.
Years ago, the aviation power plant
became a high-compression affair.
Naturally, it stimulated the research
that has led to the plug now in
more widespread use in the auto
motive field.
Boomer or later, the motor ear
buyer is going, to have to pay more
attention to his spark plugs. He
might as we'll begin with the knowl.