two leads (in distributor block). When disconnecting
ground of other lead does not stop leakage, check for
leaks between Individual leads and shielding.
Rotate crankshaft to a position that
When a recheck indicates that
distributor block may be at fault, scrub thoroughly with
acetone, Federal Specification O-A-51, dry thoroughly,
and apply a thin coat of wax Mix 1 part wax to 5 parts
maintained at a temperature of 130 to 140 °(54 to 60°C).
Repeat steps 1 through 9 above.
The low-tension system operates at
relatively low voltages (150 to 400 volts) and is not
seriously affected by moisture. Check system as follows.
harness and leads for chafing, broken conduit, corrosion,
or misaligned pins in electrical connectors at intervals
specified in inspection requirements manual.
Do not attempt to repair harness
without the proper special tools.
Damage to harness may otherwise
Tighten all loose connectors and
tape over frayed sections of nylon covered harness
Test all low tension wiring and
distributor blocks, connection plates, etc, for continuity.
Test Insulation resistance with a tester capable of
delivering 1000 volts dc (maximum) at 1 milliampere, or
an ohmmeter (20,000 ohms per volt). The insulation
resistance should exceed 1 megohm, unless otherwise
Spark plugs. The function of the spark plug
in an ignition system is to conduct a short impulse of high
voltage current through the wall of the combustion
chamber. Inside the combustion chamber it provides an
air gap across which this Impulse can produce an electric
spark to ignite the fuel-air charge. For spark plug service,
maintenance Instructions, and list of approved spark
plugs, refer to TM 55-2925-200-25.
Ignition switches. All units in an aircraft
ignition system are controlled by an Ignition switch in the
cockpit. The type of switch used varies with the number
of engines on the aircraft and the type of magnetos used.
All switches, however, turn the system off and on In much
the same manner. The Ignition switch is different in at
least one respect from all other types of switches In that
when the Ignition switch Is In the OFF position, a circuit is
completed through the switch to ground In other electrical
switches, the OFF position normally breaks or opens the
circuit. The following procedures are for Ignition switches
broken ground wires.
Tighten all loose switch and cable
terminal attaching nuts.
For specific details on any ignition
switch, refer to applicable maintenance manual.
Booster system. Starting aids such as an
induction vibrator or booster coil must be used to provide
enough voltage to the spark plug. The induction vibrator
(or starting vibrator), as shown in figure 7-19, consists
condenser, and a relay These units are mounted on a
base plate and enclosed In a metal case. The booster
coil assembly as shown in figure 7-20, consists of two
coils wound on a soft Iron core, a set of contact points,
and a condenser. General maintenance of the booster
system is described in the following procedures.
accordance with the applicable maintenance manual and
Replace defective booster coils and
all broken or frayed wiring Tighten all loose connections.
Replace magneto if impulse coupling