Evening star. [volume] (Washington, D.C.) 1854-1972, 1929-04-21
CAUSES OF ENGINE
KNOCKS EXPLAINED
So Many Kinds of Trouble
Only Expert Can dag
nose Them.
BY II. CLIFFORD BROKAW,
Automobile Technical Adviser.

Aut0m0bllS ISCHhlChb AoNASSA'
Not many people are complaining
about the lines Of automobiles that
are being produced these days. They
are beauties and eficient. There Is no
cause to knock any Of them. And tney
do less knocking themselves than mas
any generation Of cars.
But no automobile should have any
kind of q knock in its engine. II the
driver has some idea OF the various
causes Of knocking In the engine ne or
such an annoying trouble, for the Ell
fective service of q motor vehicle can
hardly be expected If there is any
knocking going on.
The motorist Is apt to conclude that
any knock which arises comes from too
great compression. There are numerous
other varieties of knocks, however. A
knock does not necessarily mean that
the cylinders are filled up with carbon,
nor can 1t be concluded that the main
bearings are loose.
There are so many different kinds Of
knocks that it really takes an expert to
diagnose a lot of them, and even an
expert may have to practically disas-
semble the engine in order to come to
q real conclusion. Some knocks which
can be heard are doing no mechanical
harm and simply represent an incon-
venience from the standpoint Of noise.
Other knocks. Of course, require i'm
mediate attention to prevent serious
damage and trouble. Some knocks are
caused from loose connecting rod or
crank shaft bearings. or lack of lubri-
cation, or broken revolving or recipro-
eating member, which might cause seri-
Gus damage II allowed to run. A spark
too far advanced puts an excessive
! strain on . crank shaft and so does a
short circuit in the ignition.
No Danger in Slap.
There is no immediate danger If
there is piston slap, although 1t may
| be noisy. The motoriSt should 60 on
the principle that when there is a
knock its cause should be found out at
the earliest possible moment and expert
advice should be secured II the owner
has any doubt as to the trouble.
Sometimes knocks are difficult to 10
cate. Such car came to my attention
recently, which evidently needed a new
cam-shaft gear to replace o worn one
which produced o knock. This matter
was attended to, but when the engine
was started again it was found that
there was a bigger knock than before
| the work was done. Finally, 1t became
evident that the knock was the result
Of the new gear. IL fitted very tightly
in the shaft and so had to be forced on.
Without being noticeable, the forcing
had cracked the hub, the crack extend
| ing through the rim, so that two OF the
teeth were out of true and had spread
enough to pound when that portion OF
/ the GEAR came into mesh
Sticking exhaust valves are sometimes
the cause of knock hard to locate.
One Of the valve stems may have been
oiled and allowed to burn to nice
sticky paste. When the push rod opens
the valve and starts down the valve
does not follow closely. The spring
brings 1t down, of course, but more
slowly than 1t should, because Of the
sticky stem, and when the stem and the
push rod meet there Is q thump.
Causes Of Knocking.
Some of the things which may cause
knocking include loose connecting rod,
bearing, crank pin bearing out Of round,
main bearings of crankshaft loose.
wrist pin loose In piston or in end OF
connecting rod, wrist pin not In line
with crank shaft, causing side slap;
piston ring loose in slot or broken, cam
follower guide worn, worn cams (lat
spot), worn or broken timing gear teeth,
piston too small for cylinder, causing
side slap, poor push-rod adjustment
(gap too great. exhaust or inlet valve
sticking in guide, fan blades striking
something and worn cylinder, causing
side slap.
Faulty ignition-spark advanced too
far, spark too late. causing overheating;
short circuits Ia ignition system, caus-
ing irregular spark, wrong timing OF
ignition system, dirt In distributor, mis-
directing current. Faulty carburetion-
pre-ignition, due to excessive carbon de-
posts; rich mixture, causing overhead
ing; lean mixture in conjunction with
worn parts. Faulty lubrication-lack Of
oil, lubricants Of poor quality, excessive
oil. causing carbon deposit.
Overheating of engine-fan not work.
ing, pump parts not revolving, radiator
clogged, pipe lines clogged, rubber hose
defective inside, blocking flow Of water;
ignition timed too late. Faulty COM
preSSion-too high, causing pre-ignition
when throttle is opened too wide at low
engine speed. The new high compress
sion or anti-knock gasoline, which may
now be obtained at most filling stations,
Is good antidote for high compress
sion knocks, which are caused by an
accumulation Of carbon, etc.
1t will be seen that there are plenty
Of possibilities Of knocking. The re-
markable situation Is that there Is SO
little trouble of this kind experienced
by the average rnotorist. This is due to
the high engineering skill which has
been applied to automobile construction
ny various manufacturers. To them
much credit Is due for the painstakina
effort which has been given this phase
OF automotive construction.