El Paso herald. (El Paso, Tex.) 1901-1931, 1917-04-14

ton and the spark. therefore, has more
kick in it.
The interrupter points usually are
adjusted for normal running speed, or
little higher than medium speed In
creaSing the number Of revolutions per
minute OF the armature causes dls-
tCrtion of the magnetic field Wnlch
4 tends to follow the armature- This
distortion is not 50 great at lower
speeds. To overcome the distortion,
which in effect twists the field around
so that the points do not open at the
period of greatest current potency, e
must change the time when the points
open and cause the spark; therefore, TO
get the best spark ii is necessary TO
have the points open earlier Widen
ing the gap between the points &C
composites this. II the engine misses
al high speed we close the points
Little 20 make the opening come later
and when in better armature position.
the action being just the reverse Of the
foregoing
Widening of Gap.
Widening the gap OF the spark plug
also viii help 10 overcome skipping at
low speeds At low speeds a fun
charge Of gas is not drawn in and
compression is low and temperature
low in consequence. the mixture Is not
so near the self ignition point when
the spark occurs as IL is al higher
speeds Therefore a better spark il
needed to ignite it BY widening the
gap in the plugs the secondary cur
rent is held back until it acquires high
enough potentlality TO jump the great
er gap; so that when it does occur an
exceptionally powerful spark is OBJ
tanned
This may be demonstrated with the
use of a vibrating coil Set one Of the
cylinders on stop OF compression ready
to ignite. Turn on the current and,
while the vibrator will buzz. the spark
inside the cylinder Is not strong enough
TO ignite the charge. Now detach the
spark plug wire and hold II close TO
the outer plug terminal and turn on
the current The extra gap will in
crease the strength Of the spark in
that cylinder and ii viii ignite the
charge, starting the engine. This has
led TO the use in some instances, OF
outside spark-gap attachments.
Widening the gap and getting a
longer spark is not what ignlJes the
charge It is simply that the greater
gap causes the current to build up to
e higher pressure, or voltage. before
II will jump the gap, so that when
II does occur il is OF greater IN
tensity.
There are several other things about
sparkling not generally understood by
the novice. The general opinion is thdt
tht greater insulating surface Of
plug there Is inside the cylinder the
less likelihood there is Of q short cir
cutting and consequently the more GER
tain will be the spark occurrences
This is only partly true; Il is true 50
far as q short circuiting Is concerned,
but where the surface IS too great and |
SCOT or carbon is deposited upon the ]
insulator surface the carbon acts as /
a condenser and absorbs the secondary |
current The effect is that II Will not |
build up a sufficiently high voltage TO /
jump the gap. Very heavy insulation
On the secondary wires absorbs current |
in the same way
Failure Of Tests.
The fact that the spark jumps across 4!
the points Of the plug when It IL IN ,
the open air does not necessarily mean l
that il Jumps when the points are I'M |
der compression in running conditions.
A current which will cause q spark to |
jump q half inch in the open air will (
only cause IL to jump q gap Of 1872 /
inch under normal running compress
sion. Failure 10 appreciate this often
results in a man thinking his ignition ,
IS all right when there may be a crack
in the insulation so small that IL |
eye when cleaning the plug, or there /
may be a porous spot in the porcelain. !
either OF which would leak current |
under compression Many manufac- !
they leak using a spark gap Of three |
quarter inch under a very high volt
age.
II there is carbon on the porcelain /
the current will travel through this /.
under high compression very often. be-
cause there is less resistance offered F.
by the carbon than by the spark gap.
II short circuits the plug and there is
no ignition. Yet when the same plug
j. removed and tested in the open air.
there viii be a good spark; the re-
sistance Of the gap in the open air
would be less than the resistance Of
fered by a path through the carbon
coating
II. on testing a plug in the way.
there seems to be good spark, yet
the cylinder will not fire. clean the
plug thoroughly and try II out in the
cylinder. If it still does not fire try
a plug which you know Is all right and
see il II fires. II il does. you may
know that the old plug leaks current
somehow and probably needs a new
porcelain. It is common error with .
motorists when cleaning a spark plug
to polish up the points and call II a 4
job What is really required Is to re- /
move all Of the carbon. which is a fair 4
conductor Of electricity from the porce-
lain or mica and get il back into the I
insulator class again.
The conditions which allow the ad- (
5ustment OF the interrupter points to I
accommodate certain speeds is mag 4
neto ignition do not arise when bat
terry ignition is used.