Piper Navajo PA-31 Service Manual page 547

236
0.422" MAX.
Figure 8B-2. Height of Spring in Distributor Block Tower
8B-18. DESCRIPTION AND PRINCIPLE OF OPERATION. The D-2230 series magnetos
feature two electrically independent ignition circuits in one housing. A single four pole rotor
provides the magnetic energy for both circuits. This magneto is designed to be used with a
starting vibrator unit. The magneto has two separate breaker cams. The lower cam operates
the main breakers for both magneto circuits. The upper cam operates the left magneto
retard breaker. Suppression of radio interference is accomplished by feed-three capacitors,
which are mounted in the magneto cover and forms a part of the magneto harness assembly.
With the magneto switches ON and the starter switch depressed, the right side of the
magneto is grounded and rendered inoperative while left side of the magneto (with retard
breaker) continues to function. At the slow cranking speed of the engine, the vibrator
provides the high energy spark necessary to fire the spark plugs. The vibrator provides
interrupted battery current to the primary coil of the magneto. The pulsating DC current is
then stepped up by transformer action, producing a shower of sparks at the plugs for
improved starting. When the engine fires and begins to increase speed, the starter switch is
released, which in turn de-energizes the starter, opens the vibrator circuit and retard breaker
circuit, thus rendering them inoperative. The right side of the magneto is no longer
grounded and thus both magneto sides are simultaneously firing in full advance.
8B-19. INSPECTION OF MAGNETO. After the first 50 hour period and every 100 hours
thereafter, the magneto ignition system should be checked. If engine operating troubles
develop which appear to be caused by the ignition system, it is advisable to check the spark
plugs and wiring first before working on the magneto. Should trouble appear definitely
associated with the magneto, the most effective measure is to install a replacement magneto
which is known to be in satisfactory condition and send the suspected unit to the overhaul
shop for test and repair. Should this not be possible, a visual inspection of the following
items may disclose the source of trouble:
Reissued: 10/12/79
POWER
PLANT
PIPER NAVAJO SERVICE MANUAL
2L1