Evening star., 1921-04-10
Answer. to Last Week. Questions.


l. There are a number of external
causes for an automobile catch.-.g
fire. such as holding an open flame
too near the gasoline tank. feed lines
or carburetor, but the usual cause,
due to a defect in engine operation.
is that of a backfire or explosion oc-
curing during an inlet stroke of one
of the piStons. when the inlet valve
is open to admit charge of fuel y
cylinder firing at such time would
ignite gas in both carburetor mixing
chamber and inlet manifold. and
would also ignite gasoline near the
carburetor- The trouble is due main
ly to wrong ignition timing or cross
ed spark plug wires.
?. Hub caps of a semi floating rear
axle are merely a protection to axle
ends and locking nuts and are to give
an ornamental finish to the wheels.
They are not means of securing
times supposed.
3. One reason why newly installed
spring leaves break soon after being
installed is because the used parts of
the spring have a different set than
the new leaves. Springs which have
been in use should be reset before
new leaves are installed.
4. An overheated and overexpand-
ed bearing or piston in an engine
may not be known until the engine has
stopped running for some time. Both
bearings and pistons in this condi-
tion have been known to give service
for long continuous run but have
seized tightly 50 that the engine
could not be revolved after a period
of rest. With newly installed parts
the trouble may be due to too tight d
fitting. but the usual cause of seizing
is insufficient fabrication.
5. Although the wood wheels of a
car require very little attention. this
attention is seldom given them by the
average motorist. They are taken as
is expected of them-untl they sud-
denly collapse. Wood deteriorates
when exposed to the elements, and
should be protected the same as metal.
Surfaces, and especially joints of wood
wheels should be coated with paint.
renewed possibly more often than the
body. When wheels are knicked or
scratched these flaws should immedi-
ately be filled or covered. This ap-
plies especially to joints or spoke ends
which deteriorate more rapidly, and if
neglected become loose, weakening the
wheel A spoke which is badly Clipped
or cracked should be replaced When
inspecting the wheel do not overlook the
hub f1ange bolts A Tightening of these
bolts when necessary may save eX-
pense and prevent a serious accident
to the car.
s. A growl developing in the diff
ferentials when the car is travelling on
level road or down hill, but which does
not occur when going up hill. may be
caused by wrong adjustment or such
trouble as the propeller shaft bolt be-
ing broken and permitting pinion gear
and shaft to move forward or back
ward. Proper adjustment would not
allow a noise to develop under these
conditions only.
z The wiring system for auto
mobile lighting considered the simplest
on three-fourths of the cars In this
system the negative terminal of the
storage battery or source of current is
connected to lamps by means of
single wire and switches. the current
returning to positive battery terminal
by means of the metal frame of the
car to which the positive terminals OF
lamps and battery are connected. Ihe
wire leading to the lamps is. of course,
insulated from the frame.
S. MagnetoS are made to revolVe IN
both the same direction as the engine
and also the opposite direction. called
clockwise and counter-clockwise The
direction of revolution of each particu-
lar magnetic is indicated by an arrow at
the drive end.
y Many OF tNe llSnteF CARS eiipios
aluminium pistons, the makers claiming
that the lighter weight piston causes
lss vibration and consequently less
friction and wear on bearings and wrist
pins Owing to the fact that the piston
Of this metal expands more than the
cast-iron piston. the former must be
fitted less tightly in the cylinder than
the latter.
TO- Vaporization is the Transforming
Of gasoline into a vapor. while carbure-
ton is the mixing of this vapor with air
suitable for combustion within the en-
gine. Vaporization is really one OF the
functions Of carburetion, as both trans
forming Of gasoline into vapor and mix
ing il with air of the right proportions
are done in one operation in the car
buretor, together with the drawing of
the mixture into the cylinder on sue
ton stroke of a piston.
This Weeks Questions
I. What causes vibration in an
anpiDe and why is it more noticeable
at certain speeds?
2 How can oil be tested to ascer-
tain II it contains impurities OF solid
nature?
8. Why should not a magnetic be
made to operate Immediately after it
has been cleaned with gasoline?
4. How can small parts rusted to-
rether be separated without injury?
5. Why is il important to maintain
the proper amount of clearance be-