Operation; Maintenance - Piper Navajo PA-31 Service Manual

PIPER NAVAJO SERVICE MANUAL
11-60. OPERATION. When the starting circuit is energized,
battery current is
applied to the starting motor terminal. Current
flows through the field coils,
creating a string magnetic field. At the same time, current flows through the
brushes
to the commutator, through the armature windings to ground. The mag-
netic force created in the armature
combined with that created in the field wind-
ings begins to turn the armature.
The gear cut on the drive end of the armature shaft extends throughthe
gear housing, where it is supported
by a roller bearing. The gear mates with
the teeth of the reduction gear that drives the bendix shaft. The shaft is keyed
to the reduction gear.
The Bendix drive is held in position on the shaft by a
"spirol" pin. The shaft is supported in the gear housing by a closed end roller
bearing and in the pinion housing by a graphitized bronze bearing.
When the armature turns the reductiongear,
the Bendix drive pinionmeshes
with the flywheel ring gear by inertia and action of the screw threads within the
Bendix sleeve.
A detent pin engages in a notch in the screw threads which pre-
vents demeshing if the engine fails to start when the starting circuit is de-
energized.
When the engine reaches a predetermined speed, centrifugal action forces
the detent pin out of the notch in the screw shaft and allows the pinion to demesh
from the flywheel.
11-61. MAINTENANCE. The starting circuit should be inspected
at regular
intervals, the frequency of which should be determined by the amount of service
and the conditions
under which the vehicle is operated. It is recommended that
such inspection
be made at least twice a year and include the following:
a. The battery should be checked with a hydrometer to be sure it is fully
charged and filled to the proper level with approved water.
A load test should
be made to determine
battery condition. If dirt and corrosion have accumulated
on the battery, it should be cleaned with a solution of baking soda and water. Be
sure none of the solution enters the battery cells.
b. The starting circuit
wiring should be inspected to be sure that allconnec-
tions are clean and tight and that the insulation is sound.
A voltage loss test
should be made to locate any high-resistance connections that would affect start-
ing motor efficiency. This test is made with a low-reading voltmeter while
cranking
the engine or at approximately 100 amperes, and the following limits
should be used:
1. Voltage loss from insulated battery post to starting motor terminal -
0.3-volt maximum.
2.
Voltage loss from battery ground post to starter frame - 0.1-volt
maximum.
Reissued: 10/12/79
ELECTRICAL SYSTEM
4C18