LOCATING TROUBLE
Any interference with the regular running of an automobile is usually
due to engine trouble, and the nature of the irregularity or the
unfamiliar noise will often give a clew to the experienced driver by
which the fault may be located. When the engine shows that something
is wrong, it is of little use to guess at the cause, for changing
an adjustment without being sure that it is the right thing to do
will probably add to the difficulty instead of remove it. The laying
out of a system for the location of a fault is not difficult, and
its application simplifies matters when trouble is encountered. By
following a process of elimination, the condition of the different
parts of the mechanism can be learned, and if on test the ignition
system proves to be operating correctly, the production of the
mixture may be considered to be guilty until that in turn is shown
to be innocent.
MAKE-AND-BREAK IGNITION
An engine equipped with the make-and-break ignition system is
always provided with a conducting bar across the top or side of the
cylinders, called a =bus bar=, connected with the source of current,
and each igniter is connected to it through a switch. If one of the
cylinders fires regularly, it is an indication that the current
is being generated properly, and that no time need be wasted in
examining the generator. By means of the switches, the igniters may
be tested individually by cranking the engine with one switch closed
and the others open. When the clutch is disengaged the engine should
run on one cylinder, and if this is the case, the igniter on the line
of the closed switch is shown to be in good condition. The opening of
this switch and the closing of the next will give a comparison when
the engine is again cranked, and if explosions occur, the igniter
points may be adjusted until the two cylinders work equally well.
If the cylinder does not operate, the stationary igniter point
should be withdrawn and its contact examined; this should be bright
and clean. The movable point should be worked by hand, to determine
whether the joint is stuck or the spring weak or broken.
If none of the cylinders show signs of explosions, the connections
should be examined to make sure that they are secure. On systems
employing a magneto alone, the wiring consists of a single wire
from the magneto to the bus bar, and the shorter wires from there
to the igniters. These wires are clearly visible, and any loose
connections or broken wires may be detected without difficulty. If
the connections and wiring are in good condition, the fault may be
located in the magneto, or, if it has recently been dismounted, its
incorrect setting in relation to the crank shaft. (See Appendix.)
If the ignition system proves to be in proper working order,
attention may be paid to the carburetor and its connections.
JUMP-SPARK IGNITION
In testing an engine fitted with the jump-spark ignition system,
the circuit should be closed and the crank shaft revolved
twice, attention being paid to the sound of the vibrators. On
a four-cylinder engine, the timer makes four contacts in two
revolutions of the crank shaft, and if all of the vibrators are
heard it is proof that the primary circuit is in good condition, and
not the seat of the trouble. If only one of the vibrators buzzes,
the battery circuit may be considered to be working properly, for
otherwise no current could have passed to the coil box. The trouble
may then be identified as being in part if not altogether in the
adjustment of the vibrators of the dead coils, their connections
with the timer, or in the timer itself. One end of a short piece of
wire should be touched to the timer binding post of one of the dead
coils, and the other to any metal part of the engine, the lubricator,
for instance, to form a short circuit through the primary circuit
with the exception of the timer and its connections. If the vibrator
buzzes, the trouble is not in the coil, but in that part of the
circuit cut out by the short-circuiting wire. The same piece of wire
may be used to bridge across to any metal part of the engine from
the binding post on the timer at which the wire from the coil is
connected, and if the wire from the coil to the timer is in good
condition, the vibrator will again buzz, showing that the fault must
be in the timer, for all other parts of the primary circuit of that
particular coil have been proven to be working correctly. A dirty or
faulty contact in the timer, or a loose connection, will probably be
the cause.
If the primary circuit is shown to be in good order, attention may at
once be given to the gasoline feed, for while the secondary circuits
have not been tested, it is extremely unlikely that the spark plugs
or their connections will prove defective on all four cylinders at
the same time.
THE CARBURETOR
Touching the primer of the carburetor will show whether the gasoline
flows to the float chamber, for if it is present it will spurt out of
the opening through which the priming stem passes. If the air inlet
is so arranged as to permit it, gasoline dropping out of it when the
carburetor is primed excessively indicates that the liquid flows out
of the spray nozzle, this part thus being shown to be clear. If no
gasoline shows around the priming stem, the feed pipe or float valve
may be suspected of being clogged, it being taken for granted that
there is gasoline in the tank and that the supply cock is open. If
it is found that gasoline is present in the air inlet, and that the
carburetor is damp with it when the primer has not been touched, it
indicates that the float chamber is flooded; the carburetor should be
taken apart for inspection and thorough cleaning.
ENGINE WILL NOT START
When the engine will not start on cranking it eight times or so,
it is useless to continue to crank it, for there is every reason
to believe that something is wrong. Too often the difficulty is in
forgetting to switch on the ignition circuit or to open the gasoline
feed. Cranking the engine slowly will not reduce the pressure in the
inlet pipe sufficiently to draw out of the spray nozzle the quantity
of gasoline required to form an inflammable mixture; quick cranking
is necessary. Too much priming will result in the formation of a
rich mixture; the gasoline should be permitted to evaporate, or the
carburetor drained, and then primed gently.
The failure of an engine to start on a cold day may be due to the
slowness with which gasoline evaporates when chilled. As it is
obviously most unwise to heat the carburetor with a flame, the best
thing to do in such a case is to pack it with cloths soaked with hot
water. A little gasoline squirted into the air inlet, or cotton waste
soaked with gasoline and held over the same opening, will almost
always permit the engine to be started; another method is to squirt a
few drops of gasoline into the cylinders through the relief cocks.
ENGINE DOES NOT DELIVER FULL POWER
Regularly occurring explosions indicate that the cylinders are
receiving the proper quantity of mixture, and that the ignition is
operating correctly. If under these conditions the engine fails to
deliver full power, which is shown by the sluggish running of the
car, the trouble may be identified as the result of a condition by
which power is absorbed between the engine and wheels. This may be
from a slipping clutch, binding brakes, or tight bearings, these more
probably on the wheels than on the change-speed mechanism or drive.
The brake rods may get out of adjustment, or the spring stick, with
the result that the bands or shoes are in continual contact with
the drums. A simple test for the condition of the brakes is to push
the car across the floor by hand; it is not difficult to recognize
unusual stiffness. This test also applies to the wheel bearings.
Engine or transmission bearings that are too tight will heat, and
a touch of the hand will show the presence of this condition. A
tight bearing should be permitted to cool before readjusting it and
proceeding.
WEAK EXPLOSIONS
Regular but weak explosions may be due to too rich or too poor a
mixture, or to the escape of compression. Cranking the engine twice
will produce a compression stroke in each of the four cylinders, and
if there is a leak, the ease with which the piston in which it occurs
may be pulled over dead center will show its presence. A little
soapy water around the spark plug, relief cock, or other opening
into the combustion space will show the escape of compression in
the formation of bubbles. A hiss inside of the cylinder indicates a
leaky piston ring, or that the openings of the rings are in line, and
when this sound is sharp and clear, the presence of a broken ring.
An additional proof of this is the undue heating of the crank case.
If the compression is correct, the carburetor may be readjusted to
improve the quality of the mixture. A poor mixture may be due to the
partial clogging of the spray nozzle or its passages, and a rich
mixture to the choking of the air inlet by dirt or dust, this being
especially liable to occur when the part is oily.
MISSING EXPLOSIONS
The missing of explosions is a common failing of automobile engines,
and while it may be due to a variety of causes, the most usual is
that the spark does not pass. It is not always an easy matter to
determine which of the cylinders is missing; if the missing is
constant, the coolness of the exhaust pipe of one as compared to
the others locates the fault. If the missing is not constant, the
difference in temperature will not be noticeable, but the one at
fault may be located by holding down all of the vibrators but one.
If the cylinder corresponding to the free vibrator runs steadily,
its vibrator may be held down and another released, this being
continued until the faulty cylinder is located. The condition
of the secondary circuit of this cylinder may be ascertained by
disconnecting the secondary wire from the plug, and holding it about
a half inch away from the plug terminal while the engine is cranked.
If no spark passes when the timer makes contact, the trouble is in
either the wire or the coil; if a spark shows, it should be of good
strength, for a current that will produce a fair spark in the open
may not have sufficient strength to produce a like result when under
compression. If a good spark shows, the spark plug may be suspected
of being fouled and thus short-circuited, of having a breakdown in
its insulation, or of there being too great a distance between its
points. The threads wear a little each time that a spark plug is
removed from the cylinder, and in order to retain a gas-tight joint
it is best not to unscrew the plug unless it is necessary.
If the secondary circuit is proven to be in good condition, attention
should be paid to the carburetor, for a poor mixture, or water
in the gasoline, will cause the engine to miss. A badly fitting
exhaust valve will permit the burned gases to be drawn back into the
cylinder, the fresh charge thus being weakened, and as the valve will
shift around on its seat, this may happen irregularly. Missing will
also be caused by a weak or broken inlet-valve spring, or by the
sticking of the inlet valve, these conditions resulting in failure
to retain the mixture in the combustion space during the compression
stroke. This pushing back into the inlet pipe of the charge will
usually produce a popping or gurgling noise that is easily recognized.
MISSING AT HIGH SPEED
If an engine runs well at low speed, but misses when speeded up, the
trouble may be due to weak battery, stuck vibrator blade, or loose
connections. A battery that will produce a good spark at low engine
speed may not be able to respond to the greatly increased demands
of high speed, and similarly, at low speed the period during which
the timer holds the circuit closed is longer than at high speed, and
the vibrator has more time to get into action before the circuit is
broken. A loose connection may be so shaken by the vibrations of high
speed as to break the circuit.
ENGINE STARTS WELL, BUT COMES TO A STOP
If the battery is nearly exhausted, it will recuperate during a
rest to such an extent that it will produce good sparks, but as
its condition of strength is only temporary, the engine will slow
down and come to a stop as the current fails. This action of the
engine may also be due to carburetor defects by which the vibrations
of running either cause the flooding of the float chamber or the
clogging of the spray nozzle, the mixture in both cases becoming
noninflammable; the condition will also result from an air-bound
supply tank.
OVERHEATING
It sometimes happens that the engine will continue to run after the
ignition circuit is opened. This may be due to a failure of the
water circulation, which is indicated by the low temperature of the
radiator, or by the low speed or stopping of the fan from a slipping
or broken belt. If the cooling system is working properly, the
lubrication must be investigated. If the oil is flowing as it should,
the cause will be found in the formation of a carbon deposit in the
combustion space, fine points of which will become incandescent
and ignite the mixture as it passes into the cylinder or as it is
compressed. A more unlikely fault may be that the points of the spark
plug are fine enough to become heated in a similar manner; modern
plugs are made with points of such size that this possibility need
hardly be considered. This ignition of the mixture by other cause
than the proper spark is termed =preignition=.
ENGINE COMES TO A STOP
If the engine stops suddenly, the fault will be found in the
accidental opening of the switch, or the breaking of a wire or
connection. An abrupt stop cannot be caused by anything but an
interruption of the ignition circuit, for the cessation of the
gasoline feed will bring the engine to a stop slowly, the gasoline
in the float chamber and spray nozzle being sufficient to permit
weakened explosions before the supply entirely fails. A slow stopping
of the engine from causes other than those previously mentioned may
be laid to defective gasoline feed, the emptying of the tank, the
clogging of the supply pipe, float valve, or spray nozzle, or the
closing of the supply cock from jolts and vibrations.
If the engine comes to a stop when there appears to be no fault with
the explosions, the cooling or lubricating systems may be at fault,
resulting in the heating of the cylinder to such an extent that the
piston sticks or seizes. Excessive heat is proof of this, the burning
or “frying” of excess oil on the outside of the cylinder being an
early warning. A seized piston may be freed by injecting kerosene
into the cylinder, and cranking, the cylinder first being given time
to cool.
NOISES
The noises made by the engine when operating properly become so
familiar to the careful automobilist that any other sound is
recognized more by instinct than by attention. Faults will often make
themselves known by noises, and these may be broadly classified as
pounds or knocks, hisses, squeaks, and rattles. A pound that occurs
regularly may be due to a loose connecting rod or wrist-pin bearing,
and in this case will be heard once to every two revolutions of the
crank shaft. A pound that occurs oftener than this may be set down
as a loose crank-shaft bearing, or a loose or cracked fly wheel. If
often happens that a fly wheel in this condition =will= make itself
heard, while sufficiently tight to show no sign of the defect on
casual inspection.
A hard metallic pound is caused by the combustion of the charge
before the completion of the compression stroke; this condition may
result from preignition or from the spark being too far advanced. If
the latter is the case, retarding the spark will stop the pounding.
Hisses are due to leaks in the combustion space, as already described.
Squeaks indicate a dry bearing, or a lack of lubrication in one of
the moving parts. The bearing may be detected by its heat. A squeak
of the leaves of a spring will often be difficult to trace and
locate, because of its irregularity.
Rattles indicate that something is loose, and should be located
without loss of time. All nuts and bolts should not only be tight,
but in addition secured in position by the use of lock nuts or cotter
pins.
Backfiring, which is an explosion of the mixture in the inlet pipe
or carburetor, may be due to a stuck inlet valve that permits flame
to pass and ignite the mixture before it reaches the combustion
space, but more probably either to ignition occurring so late that
combustion is still occurring when the inlet valve opens, or to
preignition.
Explosions in the exhaust pipe or muffler are due to the presence
of unburned mixture, which is passed out of the exhaust valve after
ignition has failed, and ignited by the heat of the exhaust pipe, or
by the hot gases from the next explosion.