Richmond times-dispatch. [volume] (Richmond, Va.) 1914-current, 1919-12-21
.S|MPL|F|ED AUTO LESSONS
nSPARK-KNOCK" EXPLAINED
BY ENGINEER GUERRllCh
PrcfRp5non Described by Expert.
Problems of Car Owners solved
in rIain Terms.

Tho expressions "spark.knock" and
carbon; knock" are well lSRown 70 mos,
motorists. yet few know the cause OF
them. The cause is that there is pre-
ignition. or that the gases arc pre-
ignitcd; or, in other words. that the
gases explode too soon.
When the car is running on the level.
or the engine, is idling, the spark
should come when the piston il in the
position shown in Zig. ]. the crank
Gated by the arrow. II the speed OF
the engine were extremely slow, as is
The case when i is being crankcd for
the piston would be driven down. and
so cause the engine 20 revolvc back
wards. or. "a Il is commonly known.
kick back.
When the engine +. turning over
fairly fast. however the weight. or
momentum. OF the fywheel. coupled
OF second 10 Ignite the gases. will
carry the piston over the dead center
before il can hr driven backward This
Is what happens when the engine IS
running idle or the car IS travelling
on the level
Advancing the Spark.
As the engine Speeds up, the spark
most power out OF the engine. il should
be made 10 come sooner. or be adj
vanced
II; however; the spark comes SO
the top as to pcrmi; the gases 10 be
completely iEnitci before the top center
is reached. the force OF the explosion
will try TO drive tho piston backward.
and The momentum OF the ilywheel
and car VIII force it TO travel on
ward. Thus there viii be a struggle
between the force Of the explosion.
which tends 10 drive the piston back
ward. and the momentum or the ny
wheel, which tends 10 drive the. piston
forward.
II .bcrc ha .ba clicL.ne. 'on,,,,,,
wear in the wrist pins or bearings the
result OF tho above mentioned sirug-
Eie wili De = bad knockins noise in
advanced spark. IS called Il spark
knock.
The sparkknock seldom comes when
the engine is idling. as then the charge
OF gas is small. requiring a longer
time TO ignite. and the speed Of the
piston is comparatively great On a
slowed down because of the load not
only will the piston lie travelling slow
so that full charge is taken into inc
cylinders, which Will result in a very
powerful and quick explosion Thus
the struggle between the force o, inc
back and tho nywhecl trying 10 force
Il forward Will he great II the spark
Is too far advanced. and knock Will
result.
Lever Should TIC Freely Used.
From the above We see that tho
spark control lever should pe freely
used In order 10 prevent a back
or by tho self-starter. the snn,-i nIs
hc fully retarded and advanced as the
engine IS speeded up: On hill the
spark must be gradually retardc (not
necessarily fun way) as the engine
slows down. II tho gears are shifted
10 second or low, the spark should be
Immediately advanced again
y mock, which will no al
acuy. like the spark knock. but from
4 dlfcront cause, is the carbon knock
Let us sec the reason for this knock
The carbonk knock is due to particles
Of carbon becoming heated white no,
ny the burning gases and so ignitins
and the piston is in the proper position
for the ignition.
Pcrhaps YOU wonder Why ,h;. white
hot carbon does not ignite the gases as
They enter on the suction stroke hut
waits until the gases have been partly
c"mDressed. There are two reasons for
this.
It takes certain temperature TO
ignite the gases a temperature higher
than that which III" whi,e-hot carbon
mas. SO that the entering gas will no.
~" icni'cd. When gases arc compressed
however quite little heat Is generated
and this heat, when added 20 tho heat
OF the carbon, Will be enough IT some
point OF the compression. to ignite the
gases: thus causing a too-carly cxpIo-
SION 1nst as tho too-far- advanced sDa-k
tfcn before The proper time
MANY stationary gas engines Nave mn
electrical ignition svs'ern bur have in.
stead what is called "a hot-tubc lgrf-
t'on. IN these hollow tuha is screwed
INFO the compression chan,he- o. the
engine. and fame constantly c'ave1
Upon Il 50 aS 20 Reer IL white not T,a
mixture Is mus igni'ei nv 'his tube Jus,
as me carhoN iEn ted N. gas-.s "a er-
3iained above n ;h@se engine. the
compression s 'ow. that to '.ri
ton Vii take place sligh,ly hefor- ~
pisto7 reaches o"ad center
ZION the aNo-'.. ,ta-- ma. yh.,
AT s1F'-@ k-0''t { Or ri'l yrhf'a ~.
Fnars IS r-o1e-'y -sv-rI"i. .ha. 500
j 90 rnUrh p. tor r. -. r,-t-aa.s
Vslon c,-Son Nus, ~ removed
correct Way 10 Remove Carbon.
ne only correct way 70 -arnove re
f1n is . nave sc-ap=d out though
.avihE i burned ou, win ory.en vii
. give Eoc1 results. This xo-L mus,
aohe y eare.ul mechanic. Is
c'iH' Use the engine may b. harmed
SINAI! amount .. CARRIER 49, J.,
.orec wtttls' by. pouring about ,--re
o. iolr = rl~s. oo1tVls q KEROSENE i-,o
!; rpo and the engine - Gu!.. no., T,s
reroshne should he ,er, in ove-,fg,