Starter motor troubles can be traced for the most part
to the commutator, brushes, or insulation. If motors are
to function properly, they must be kept clean and dry.
Dirt and moisture make good commutation impossible.
Dirty and fouled starter motors may be caused by failure
to replace the cover band, by water leakage, or by excess
lubrication.
Most starter motors have a cover to protect the
commutator and windings. If you neglect to replace the
cover or remove it as an aid to ventilation and cooling,
dirt and water are sure to damage the equipment.
Although lubrication of bearings is essential for
proper operation, excessive lubrication may lead to
trouble in a starter motor. Excess lubricant in the shaft
bearings may leak or be forced past the seal and foul the
insulating material, commutator, and brushes. The
lubricant prevents a good electrical contact between the
brushes and the commutator, causing the commutator to
spark and heat and the brushes to burn.
Burned brushes are another possible source of
trouble if the starter motor is inoperative. Burning may
be caused by loose brush holders, improper brush spring
tension, a brush stuck in the holder, a dirty commutator,
improper brush seating surface, or overloading the
starter.
STARTER MOTOR OPERATES BUT DOES
NOT CRANK ENGINE
If the starter motor and battery are in good operating
condition but the starter fails to crank the engine, the
trouble will usually be in the drive connection between
the motor and the ring gear on the flywheel. Troubles in
the drive assembly are usually in the form of broken
parts or a slipping clutch (if applicable). A slipping
clutch may be the result of the engine not being free to
turn or of the clutch not holding up to its rated capacity.
Even though seldom encountered, a stripped ring
gear on the flywheel may be the source of trouble if the
starter motor does not turn the engine.
ENGINE CRANKS BUT FAILS TO START
Starting troubles and their causes and corrections
may vary to some degree, depending on the particular
engine. If the prescribed prestarting and starting
procedures are followed and a gasoline engine fails to
start, the source of trouble will probably be improper
priming or choking, a lack of fuel at various points in
the system, or a lack of spark at the spark plugs.
Improper priming may be either underpriming or
overpriming. Priming instructions differ, depending on
the engine. Information on priming also applies to
engines equipped with chokes. A warm engine should
never be primed. Some engines may require no priming
except when they are started under cold weather
conditions.
On some installations, underpriming can be
checked by the feel of the primer pump as it is operated
On other installations, underpriming may be due to
insufficient use of the choke.
Over-priming is undesirable because it results in a
flooded engine and makes starting difficult. It also
causes excess gasoline to condense in the intake
manifolds, run down into the cylinders, wash away the
lubricating oil film, and cause pistons or rings to stick
You can determine flooding by removing and
inspecting a spark plug. A wet plug indicates flooding.
If you find the engine to be flooded, be sure to dry out
or deflood it according to prescribed instructions. Some
installations specify that the ignition switch must be ON,
while others state the switch must be OFF; therefore it
is important for you to follow the engine manufacturers
instructions.
Improper carburetion may be the source of trouble
if a gasoline engine fails to start. On some engines a
check of the fuel pressure gauge will indicate whether
lack of fuel is the cause. If the gauge shows the
prescribed pressure, the trouble is not lack of fuel; if the
gauge shows little or no fuel pressure, you should check
the various parts of the delivery system to locate the
fault.
In some installations, you can determine whether
the trouble is in the gauge or in the fuel system by using
the following procedure: (1) remove the carburetor plug
next to the fuel pressure gauge connection; and (2) use
a suitable container to catch the gasoline, and operate
the pump used to build up starting fuel pressure. If fuel
is reaching the carburetor, gasoline will spurt out of the
open plug hole; this indicates that the gauge is
inoperative. If no fuel flows from the plug opening, the
trouble is probably in the fuel system somewhere
between the fuel tank and carburetor. Even though all
installations do not have a fuel pressure gauge, the
procedure for checking the fuel system is much the
same.
If a wobble pump is installed to build up starting fuel
pressure, you can determine whether the pump is
operating correctly by the feel and sound of the pump.
If the pump feels or sounds dry, the trouble is between
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