The sun. [volume] (New York [N.Y.]) 1916-1920, 1919-03-16

combination types Is that there is double
protection, 50 that If one insulator be-
comes broken the other will prevent
current leakage. In buying a plug you
cannot tell by looking at the iusula tor
whother II is good or not. because some
cheap stone looks Just like good ma
terial The reliability Of the maker is
the thing to consider.
Electrodes must be of such material
as not to be quickly affected by heat,
spreading and changing the gap size, or
burning away altogether. Nickel wire.
or similar high heat resisting wire,
usually Is used. but the car owner should
take note of the thickness of the cleo
trodes.~ Thick ones last longer than
those Of small diameter.
The commonest trouble with spark
plugs Is caused by cracked lnsulators,
which then allow of current leakage,
causing a poor spark or none at all at
the gap. Often one cannot tell by ex-
aiming the outside whether the insu-
lator Is cracked, because the trouble may
be in the, hidden portion. The only
safe way Is either to dismantle the plug
IL 1t is not of the one-piocs type or
test is by laying 1t on the cylinder head
with the plug cable attached. Then
by cranking the engine the gap may be
watched for a good spark. Cracks, ex-
cept hidden ones, may at once be noticed
II the engine Is operating IN dark
area sparks will be seen on the outside
of the insulator.
Fouling is another plug trouble. This
term refers to the carbonizing OF the cleo
trode ends and bottom of the insulator.
resulting in a short circuit since the cur
rent will pass through the carbon in
stead of Jumping the gap which offers
greater resistance. The carbon de-
posts in troublesome quantity, because
oil is splashed on the plug, and II the
plug is of tho sort which retains the oil
carbon forms there. It is usual TO hook
shape the ground electrode so that oil
will tend to dow away from the gap.
! When plugs become carbonized they
should be cleaned by immersng in kero-
sene and then removing and scraping
the carbon off. The scraping may be
done with a knife, but care should
be taken not to roughen the parts, as
this makes a good footing for moro car
bon. When plug fouling persists the
cause should he gone into--probably
leaky plstons rings, too much oil. too
thin an oil, worn or pltted cylinders. So
The gap at the plug end must be prop
erly set. The usual gap Is 1872 inch,
but this will vary slightly. in different
engines. II the gap Is too short the
spark may be too weak; II the gap Is
too wide there may not be sufficient
VOLTAGE to cause the current TO jump
It The gap is easily adjusted by slight
bending OF the ground electrode.
A spark plug should be not removed
or taken apart unless II is giving trouble
or thought to be giving trouble. Oc-
casionally squirt oil around the plug
Joints and watch to see II there Is any
leakage OK gas Bubbles will appear II
there Is leakage. At the shell to cylin-
der Joint this may he caused by poor
gasket, dirty gasket, or worn gasket.
or the plug not being screwed In tight
enough. II the plug is of two parts
the gasket at the Joint may be dirty or
bent, or the check nut may not be tight.
The right length OF plug should al
ways be used. II must have the points
just below the level of the cylinder head
and not in a pocket where dead gases
always exist. 1t also must not stick too
far down. Find out the best type for
your engine and always ask for that
no matter what make you get Avoid
sensational types which are said &c
spark even IL carbonzed and to give
more than one spark. IF they are car
bombed the current will go through the
carbon and not where the maker says
it will.
Never throw spark plugs haphazard
into the tool box. where they may be-
come cracked. mover throw an old plus
| away. Save the old ones and buy spare
insulators " electrodes and save money.