Cessna 1969-1976 172 Series Service Manual page 170

Figure 11-4. No.
e. Be sure magneto gasket (right magneto), mag-
neto adapter and gaskets (left magneto) a r e in place
and that the engine is in the correct firing position,
then install magneto approximately
at
the angle noted
during removal, tighten mounting nuts finger tight.
NOTE
Remove timing pin (or nail) from magneto,
i f
installed. Be sure to remove this pin before
rotating propeller.
f . Connect
a timing light to the capacitor (primary
lead) terminal at the r e a r of the magneto and to a
good ground.
rotation a few degrees (approximately 5 degrees) to
close magneto contact points.
NOTE
g. Rotate propeller opposite to normal direction of
Do not rotate propeller back far enough to
engage impulse coupling, o r propeller will
have to be rotated in normal direction of
rotation until impulse coupling releases,
then again backed up to a few degrees be-
fore the firing position.
h. Slowly advance propeller (tap forward with min-
ute movements as firing position is approached) in
normal direction of rotation until timing light indi-
cates position a t which contacts break. The contacts
should break a t the advanced firing position of num-
ber one cylinder. Loosen mounting nuts slightly and
rotate magneto case to cause the contacts t o break a t
the correct position. Tighten mounting nuts.
After tightening magneto mounting nuts, recheck
timing. Make sure both magnetos a r e set to fire a t
the same time. Remove timing equipment, install
i.
1 Magneto Outlet
spark plugs and connect spark plug leads and ignition
switch leads.
NOTE
Beginning with the number one outlet, the mag-
neto f i r e s a t each successive outlet in
a counter-
clockwise direction, looking
at
the outlets. Con-
nect number one magneto outlet to number one
cylinder spark plug lead, number two outlet to
the next cylinder to fire, etc. Engine firing
order is listed in paragraph 11-8.
11-58. MAINTENANCE. Magneto-to-engine timing
should be checked a t the first 50 hours, first 100
hours and thereafter a t each 200 hours. If timing to
the engine is not within plus zero degrees and minus
two degrees, the magneto should be retimed to the
engine.
NOTE
If ignition trouble should develop, spark plugs
and ignition wiring should be checked fir st. If
the trouble appears definitely t o be associated
with a magneto, the following may be used to
help disclose the source of trouble.
a. Remove high-tension outlet plate and check dis-
b.
If any moisture is evident, lightly wipe with a
tributor block for moisture.
soft, dry, clean, lint-free cloth. Install outlet plate.
NOTE
Since these magnetos MUST NOT BE DIS-
ASSEMBLED, a new magneto should be
installed i f the moisture check does not
remedy the trouble.
11-20