The sun., 1919-05-18
WHY SOME PARTS
BREAK DOWN EARLY
Some knowledge Of Stresses
"a and Strains Will Help
'sssf Car Owner.

Every automobile owner at one time
ar another has had occasion to study q
repair bill for replacement Of broken Or
injured parts. and once, at least. has
endeavored to show the manufacturer
that the failure was due to poor ma
teEiaL" When a part breaks for no APP
pRrent reason the owner comes to the
conclusion that the material was poor
A.frecent case OF axle trouble will Illus
frate the point. An owner broke i've
differential ring gears in succession and
not one lasted more than six months.
three of them only few huhdred miles
This owner insisted that the gear ma
terial was OF an inferior grade and
promptly told the car maker so, but an
Investigation showed that the ring gear
was not running true, that there was
point contact OF teeth, and even the
strongest nickel steel gear might break
down under such conditions.
II Is quite true that many parts such
"a axle shafts. motor supports. crank
sh1fts, pistons, &c, may break II the
Material Is of poor quality. but in the
majority of cases even the poorest grade
otI;metal for that particular part will
stkhd up for a long period. The design
ofpthe part has as much to do with
bukAkage as the material from which 1t
isssnade, assuming OF course that proper
lutficating conditions are maintained.
IA may be difficult for the owner OF
an automobile to understand why tool
mkflxs on an axle shaft cause breakage,
J btt as a matter OF fact this may actually
5Skthe case. Tool marks on a bearing
s,fsface is exactly like having few
huh spots to take the wear and strain.
L6pking at the part with the naked eye
itfss hard to see why II should break
bscause of few grooves In 1t. A
hEhly polished surface has greater
ain of contact than an unfinished sur
f&ee, hence 1t will not wear so much
atd can stand up for longer period.
- this reason many cheap cars,
Though made of good materials and well
( dt1igned but cheapened by labor saw
id give a lot of trouble In smaller
pafts Closely allied with mere tool
Marks as a cause Of breakage comes a
d<sign Serror which employs sharp cor
nkfs instead of rounded corners. III
sou will leok at the wheel spindle Of
your car you may notice that its inner
most end is rounded Off instead of
squared Off Where 1t is squared OF
the chance of breakage is greater. The
accurate finishing of parts and the
rounding OF corners all take time ana
cost money, hence II is not usual to
find this carried out to a great extent
on any but high grade cars.
Vibration is another common cause OF
failure. Crankshafts perhaps more than
any part receive a great deal OF vibra-
. ton because OF the various forces act
ling on this part and the speed at which
IL runs. In some cars which habitually
misfire this vibration becomes greater
and the chances for breakage are In
creased. IL the shaft Is too small and
10 not we'll designed in so far as Its bal
ance Is concerned it may break In
very short time. Even the heaviest
Z crankghaft, however. made twice as
thick as usual and made of superior
materials may break more easily than a
cheap shaft IL attention Is not paid to
balance. We say that internal stresses
break the shaft. 1t is not easy for the
owner to, understand how a heavy and
apparently stiff piece OF high Grade
= metal can bend and twist all out OF
shape due to vibration and unbalance
but such Is actually the case in the
engine crankshaft. II you will remem-
Der that even slight hand pressure or
table or even a stone wall causes q
slight (though not measurable compress
sion) 1t will be easy to see how the
many tons pressure TO which crank
shaft is subjected at times may cause
the shaft to bend out OF shape.
There is another cause of failure In
parts, namely that due to a weak sec
tion or use of too little metal. Every
time hole is bored in a piece OF metal
II weakens it just that much. The more
metal the stronger the part. Some carr
have parts so small In section, or thick
ness, at places that they soon break a,
that weak spot. Where small sections
are used for lightness the maker must
resort to the use of betten quality ma
terial and better finish of the part
spoke previously OF point contact OF
parts. Take any bearing and put q
piece of sand on it and for the time the
sand particle is there it takes the whole