Piper Navajo PA-31 Service Manual page 552

PIPER NAVAJO SERVICE MANUAL
d. The magnetos incorporate a built-in pointer and a degree wheel with sufficient
reference to assist the user in magneto timing procedures. Printed upon the rotating magnet
are marks to indicate magneto neutral and magneto "E" gap (8°). (Refer to Figure 8B-6.)
Also included are retard angle references of 15°, 20° and 25°. These marks are set up for
either clockwise (R) or counterclockwise (L) rotation of the magneto as viewed from the
magneto drive end. The timing tooth of the large distributor gear is marked with red paint.
(Refer to Figure 8B-7.)
NOTE
A magneto, correctly timed internally, will have the timing
teeth of the large distributor gears approximately centered in
the timing windows, the R or L ("E" gap) mark on the rotor
in alignment with the pointer, and both main breaker points
opening, all at the same time. These three references, "E"
gap, painted teeth, and point opening, are all used when
timing the magneto to the engine.
e. Install the magneto to engine gasket on the magneto flange.
f. Remove engine to magneto drive gear train backlash by turning the engine magneto
drive as far as possible in the direction opposite to normal rotation.
g. Remove the timing window plug from the most convenient side of the magneto
housing (refer to Figure 8B-7) and the plug from the rotor viewing location in the center of
the housing. (Refer to Figure 8B-8.)
h. Turn the rotating magnet drive shaft in the normal direction of magneto rotation
until the painted tooth of the large distributor gear is centered in the timing hole. Observe
that at this time the built-in pointer just ahead of the rotor viewing window aligns with the
R or L mark on the rotor, depending on whether the magneto is right or left-hand rotation
as specified on the magneto nameplate.
i. Hold the magneto in this position (No. 1 firing position) and install the magneto to
the engine and loosely clamp it in position.
j.
Using the Bendix timing light (Part Number 11-9110), attach the red lead to the left
switch terminal outlet on the magneto cover and the green lead from the timing light to the
right switch terminal. Short adapter leads connected to the switch terminal outlets will
facilitate the hookup. (Refer to Figure 8B-9.)
k. Turn the entire magneto in the direction of rotor rotation until the red timing light
comes on; then rotate the magneto in the opposite direction until the red light just goes off
indicating left main breaker has opened. Then evenly tighten the magneto mounting clamps.
1. Back the engine up approximately 10° and then carefully "bump" the engine
forward at the same time observing the timing lights. At the No. 1 firing position of the
engine, the red light should go off indicating the left main breaker opening. The right main
breaker, monitored by the green light, must open within ± 2 engine degrees of the No. 1
firing position.
m. Repeat step k until the conditions described in step 1 are obtained.
n. Complete tightening the magneto securing clamps to standard torque value. Recheck
the timing once more and if satisfactory disconnect the timing light and remove the adapter
leads.
Reissued: 10/12/79
POWER PLANT
2L6