LOCATING TROUBLE
There are many ways in which an engine can give trouble, but these are
not serious to an operator who understands the action of an engine,
and who works with his brain as well as with his hands. Each of these
troubles has a distinct cause; proper care will avoid them, but if they
come the reasons for them can be determined by simple tests.
In order to develop full power, an engine must be in good mechanical
condition; that is, the bearings must be free without being loose,
the gears must run well, the pistons and their rings must not bind or
be too free, and so on. It must be properly lubricated and cooled,
compression must be correct, it must get a good mixture, and ignition
must take place at the right time. If an engine gives trouble, it is
because one of these systems is not working properly, and it is not at
all difficult to locate the cause and to correct it.
If an engine gets a good mixture, which is ignited properly, it will
run; if it will not give any explosions it is because one or the other
of these systems is not working properly. An inspection or a simple
test will show which one is at fault.
ENGINE WILL NOT START
If an engine will not start after being cranked a dozen or twenty
times, it is useless to continue to crank it. It is not getting either
a proper mixture or an ignition spark, and it saves time and energy to
find out where the trouble is, rather than to keep on cranking in the
hope that something may happen.
When a tractor engine refuses to start, the trouble is usually with the
mixture, and, more often than not, this is due to carelessness or to
forgetfulness. The tank may be empty, or the fuel valve may be closed,
so that the carburetor is dry; see if there is fuel in the carburetor
bowl. The engine may have been shut down while running on kerosene,
instead of having been switched to gasoline for the last few minutes of
its run, so that the carburetor, intake manifold and cylinders contain
kerosene, which will not vaporize without heat, instead of gasoline,
which will. In this case the engine must be primed with gasoline.
If too much gasoline has been used for priming, the cylinders may
contain a mixture that is too rich to ignite; the engine should then be
cranked briskly with the fuel shut off and the compression relief cocks
open, to clear out the rich mixture and fill the cylinders with air.
Water in the fuel will make starting difficult or impossible. It is
easy to forget to shut off the water valve of the carburetor when
stopping the engine, and when starting, water from this valve will
prevent the forming of a mixture and will also interfere with the
ignition.
If the mixture is apparently all right, the fault may be in the
ignition. A drop of liquid fuel or of water, for instance, may be on
the spark plug points; this will short-circuit them and no spark will
be formed, although the sparking current is passing.
If there is a suspicion that the ignition system is at fault, and that
the magneto is not producing a sparking current, it should be tested,
as explained in Chapter XII.
Starting in cold weather is always more difficult than starting when it
is warm. Helps in cold weather starting are given in Chapter XI.
A leaky inlet manifold will admit an extra amount of air that will
completely alter the proportions of a mixture. Thus the mixture will
be wrong, although the carburetor adjustment seems to be correct.
Manifold leaks are usually at the joints, but occasionally a manifold
is found with a hole in it due to poor casting or material, or a crack
may develop.
Difficulty in starting due to poor compression caused by stuck valves
or rings will show its cause by the ease with which the engine can be
cranked.
If an engine is free enough to turn over, poor lubrication or cooling
will not interfere with starting it. Faults in these systems show
themselves only when an engine is running.
ENGINE LOSES POWER
An engine will lose power through a defect of compression, carburetion,
ignition, cooling or lubrication, or because of a mechanical fault.
If the trouble comes from cooling or lubrication, the engine will
overheat and thus make the cause known. A bearing that binds will
become very hot, while if the cooling system fails, the engine will be
hot all over. When the engine is excessively hot, the pistons will
expand, and much of the power of the engine will be used up in forcing
them to move.
An engine that is not hotter than usual, and is having regular and even
explosions, probably loses power through a loss of compression. This is
the most usual cause of this trouble, and it is located and remedied as
explained in Chapter XII.
If compression is good, the loss of power may be due to a clogged
muffler or exhaust pipe, which will not permit the free escape of the
burned gases. This condition will prevent full charges of fresh mixture
from entering the cylinders, and the engine then cannot be expected to
deliver full power.
Another possible cause of a loss of power with the engine apparently in
proper condition is the sticking or poor adjustment of the governor.
The factory adjustment of the governor should not be changed, however,
until it is definitely proved that that is where the trouble lies.
If the engine misses fire, or runs irregularly, the loss of power
will be due to faulty carburetion or ignition. The mixture may be
too rich or too lean; in either case the trouble will be remedied by
readjusting the carburetor. A mixture that is very much too lean will
make itself known by _backfiring_; there will be little explosions at
the carburetor. This should be remedied at once, for the danger of
fire from it is very great. Black smoke at the exhaust is a sign of a
mixture that is too rich.
An engine will not deliver full power if it is run on a retarded
spark. A loss of power from this cause will be accompanied by general
overheating of the engine.
ENGINE STOPS
The manner in which an engine stops will indicate the reason for it.
A failure of the ignition system that stops the formation of current,
like the sticking of the circuit breaker lever, will cut off all
explosions instantly; the engine will stop abruptly. An engine will not
stop abruptly from any fault with the mixture; with mixture trouble the
explosions will become weaker and weaker until they cease.
If an engine stops through a failure of the lubrication or cooling
systems it will be intensely hot, which will not be the case if the
fault is with carburetion or ignition.
A running engine will not be brought to a stop by a loss of compression.
ENGINE MISSES
A steady or irregular miss in one cylinder is usually due to the spark
plug’s being cracked or dirty. Carburetor trouble will affect all the
cylinders; it cannot affect one cylinder only, and missing in one
cylinder may be put down as ignition trouble. In this case ignition
trouble does not mean magneto trouble, for if the magneto produces
sparking current for one cylinder it will produce it for all. Therefore
ignition trouble in only one cylinder is in those parts of the
ignition system supplying that cylinder; that is, in the spark plug or
in the spark plug cable.
A less likely cause for missing in one cylinder only is poor
compression. It is usually the case that if compression is poor in one
cylinder it is poor in them all, but a broken valve or piston ring or a
weak valve spring will weaken compression in one and not in the others.
A cylinder that misses is cooler than the others, and can be located by
feeling. It can also be located by short-circuiting the spark plugs one
at a time; this will make no difference in the dead cylinder, but when
the spark plug of an active cylinder is short-circuited the speed of
the engine will drop.
To short-circuit a spark plug, take a wooden-handled screwdriver or
other tool and rest the blade on the engine near the spark plug; then
tilt until its shank is close to the spark plug terminal. The spark
current will then pass to the metal of the engine by way of the tool
instead of by the spark plug points. This is also a test of ignition,
for a spark will pass between the terminal and the tool.
Irregular missing in all cylinders may be due to a fault at one of
the parts of the ignition system that supplies them all; a dirty
distributor, for instance, or a sticking circuit breaker lever, or
rough platinum points. It may also be due to a clogged fuel line, which
prevents the carburetor from getting a regular and sufficient flow.
Irregular missing will also be caused by loose ignition connections,
and by loose switch parts.
ENGINE STARTS; BUT STOPS
When an engine starts readily but quickly slows down and stops, the
reason is almost always an insufficient supply of fuel. An obstruction
in the pipe may prevent the fuel from flowing fast enough to keep the
carburetor bowl filled when the engine is running; when the engine
starts, the fuel is sucked out of the spray nozzle faster than it comes
in through the float valve, so the carburetor is soon drained and the
engine stops. The bowl then fills, only to be sucked dry again when the
engine is next started.
This difficulty is caused by dirt in the fuel, which collects in the
strainer or the fuel pipe. The strainer is so arranged that it may be
easily drained and cleaned; to clear out the pipe, shut off the fuel at
the tank, disconnect the pipe at both ends, and blow through it.
The strainer should be drained every day; it is sufficient to open the
strainer drain cock for two or three seconds.
Most of the troubles due to dirt in the fuel will be avoided if the
fuel is strained when filling the tank.
Another thing that will bring an engine to a stop is the clogging of
the vent holes in the tank filler cap and in the top of the carburetor
bowl. These holes should be clear, so that air can enter to replace
the fuel that is used; if air cannot enter the fuel will not flow, and
the tank is then said to be _air-bound_.
ENGINE OVERHEATS
An engine may overheat either because it produces more heat than the
cooling system can take care of, or because the cooling system is not
taking off all of the heat that it should.
Running an engine with the spark retarded will cause it to overheat; so
will a failure of the lubrication and an obstruction to the passage of
the exhaust gases.
If an engine has been taken down and overheats when it is reassembled,
it may be that the magneto has been wrongly timed, and produces its
spark too late. If an engine has been running properly but begins to
overheat, the ignition cause will be the faulty setting of the spark
control, or the slipping of the spark control rod.
When an engine is run on kerosene, the oil in the crankcase must be
frequently drained off and replaced with fresh oil. The reason for
this is that part of the kerosene that goes to the cylinders does not
vaporize and burn, but works its way past the pistons and into the
crankcase, where it thins the lubricating oil. As the oil thins, it
loses its ability to lubricate, and the engine begins to overheat.
Anything that produces extra friction will cause overheating, as, for
example, a wrist pin that works endways and rubs against the cylinder
wall, or a tight bearing.
For a cooling system to work properly it must contain a full supply of
water, the passages must be clear, sufficient air must pass through the
radiator, and the pump must be in proper condition.
Hose connections will rot, and a strip of rubber may peel off the
inside and be drawn across the passage; or if dirty water is used, the
dirt may choke the fine radiator passages or other channels. If the
radiator is covered with mud, air cannot get at the tubes to take the
heat from the water that they contain.
A very usual cause of overheating is a slipping fan belt; an adjustment
is provided by which the belt can be tightened when it works loose.
ENGINE SMOKES
Black smoke indicates that the mixture is too rich; blue smoke is a
sign of too plentiful lubrication. Oil that is too thin, or that is
of a poor grade, will cause smoking; good quality oil of the grade
recommended by the manufacturer should always be used.
Broken piston rings, or rings stuck in their grooves, will be the cause
of smoking because they will permit an excess of oil to pass by them.