Evening star. [volume] (Washington, D.C.) 1854-1972, 1922-02-26
FOUR GENERAL CAUSES GIVEN
FOR ELUSIVE MOTOR ''KNOCK''
Spark, Overheating, Carbon and Loose or
Worn Parts Bring Trouble, Often Hard
to Locate, But Easy to Remedy.

knock. as already explained. 1t Will
be evident from " hat has gone before
that the three cases just considered.
spark overheatine and carbon KNOCKS.
can all be classified under the head
of preiGnition. because the explosion
occurs before dead center. Il carbon
is SUSPECTED it is All easy matter TO
remove the spark plug ana inspect
tie end of 1t or TO glance INTO TIE
cylinder. 1t accumuiates first around
the exhaust valve and from there
spreads to al rait IS of :h' cylinder
ard piston head. When il becomes
troublesome It should jbc removed I'M
meiiateiy. AS it is q Serious cause Of
loss Of power.
We now come TO q totally different
cause or causes of kuocking--loose
or worn parts. This covers all of the
mechanical parts Of the engine. The
knock may he heavs. as from a main
bearing being loose or burned out;
not so heavy. as from loose connect
ing rod. or very light. as from valve
tapDet, As the valve tappetS are the
only parts accessible from the outside.
The engine must come down TO locate
ANY Other knock. The investigator
, may get general idea Of the nature
o. the knock and its iocation by hold
ing a piece Of dor:elins or IA ligh:
steel rod against different parts OF
the engine. the other end resting
against his ear. after the manner Of
Il stethoscopc. This is merely an aid
to diagnosis. as the engine must come
i down for repairs.
Harmless Knocking.
There is one knock which does no
harm. but is simply annoying. That
is piston slap or knock. 1t il due to
the pistons and cylinders being so
badly worn tnat there is enough play
between them to make a noise. Tas
: does not harm and is usually NEGLECT
, ed. as il requires regrind!ng of the
cylinders and the fitting Of larger piS-
tons to remedy it. But the engine
must come down to determine wheth-
i er the knock is due 10 this or some
other cause
! An occasional knock is ca sad by
/, dry cylinder walls. This viii cause a
! slight knock at firs;, but the oil soon
works up and the knock stops. Then
a slight knock. which starts when
the engine starts and soon disappears.
can he disregarded.
We now come to the question Of
deciding which one of the above
causes is producing the knock. Ex-
perienced repair men can usually tell
| by listening carefully and trying out
! the car for a few minutes on the
! road. The best way for the beginner
, IS to go over the above lis; III the
! order named and eliminate one cause
i after another until the cause is found.
4 spark knock can be stopped by
retarding the spark. An overhcatnS
! knock is always accompanied by
symp: oms of overheatinS. A carbon
knock will be shown by carbon on
| the spark plugs and in the cylinders.
| II none of these causes are present.
! the trouble is due to loose or worn
parts and should be left to an expert
enced repair man to correct. There
are over a hundred places where
knocks may occur in an engine. and
we shall not give the list here, as it
| might look discouraging to the nov
| ice. With so many parts to an en-
CINE whic Knight come loose 1t is
surprising that so few Of them do 50.
1t speaks we'll for the skill and care
given to these parts when they are
assembled. Present methods of Sc
curing nuts and bolts are very reli-
able excellent material goes into the
| construction and the workmen are
conscientious. The result is an en-
CINE which gives very little trouble
| in view of all the arrangements which
might arise.
QUESTIONS AND ANSWERS.
To the Automobile Editor:
Please answer the following in your
interesting and helpful column: I
have a runabout which gives me much
trouble with the packing between
the cylinder and cylinder head.
have repacked it several times with
the copper gasket and moboline gas
ket supplied by the makers Of the
machine. Have also roughed the face