8A-25. IGNITION SYSTEM MAINTENANCE.
8A-26. MAGNETO.
CAUTION
Ascertain that the primary circuit of both magnetos is grounded before
working on the engine.
8A-27. INSPECTION OF MAGNETO.
WARNING
When servicing or inspecting vendor equipment installed in Piper Aircraft,
it is the user’s responsibility to refer to the applicable vendor publication.
NOTE
Comply with latest revision of Bendix Service Bulletin No. 608 at first
o p p o r t u n i t y, but no later than next magneto overhaul. Install self-locking
cam retaining screw (10-391213) and torque to 21-25 inchpounds. If self-
locking screw is removed at any time always replace with new self-locking
screw and torque to the specified value.
a. After the first 25 hour and 50 hour periods, and periodically thereafter, the contact assemblies should
be checked. Examine the points for excessive wear or burning. Points which have deep pits or
excessively burned areas should be discarded. Examine the cam follower felt for proper lubrication. If
necessary, points can be cleaned by using any hard finished paper. Clean breaker compartment with
dry cloth.
b. 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 magnetos.
c. Should the 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.
d. Should this not be possible, a visual inspection may disclose the source of trouble. Remove the harness
outlet plate from the magneto. Inspect for the presence of moisture and foreign matter on the rubber
grommet and high tension outlet side of the distributor block. Check height of block contact springs
(0.422 maximum from top of the block tower to the spring). Also check for broken leads or damaged
insulation. If either is present, remove magneto and replace with one known to be in satisfactory
condition.
e. Remove the breaker cover and harness securing screws and nuts and separate cover from magneto
housing. Check contact assemblies to see that cam follower is securely riveted to its spring. Examine
the contact points for excessive wear or burning. Figure 8A-8 shows how the average contact point
will look when surfaces are separated for inspection. Desired contact surfaces have a dull gray, sand-
blasted (almost rough) or frosted appearance, over the area where electrical contact is made. This
means that points are worn in and mated to each other, thereby providing the best possible electrical
contact and highest efficiency of performance.
f. Minor irregularities or roughness of point surfaces are not harmful. (Refer to Figure 8A-8, center. )
Neither are small pits or mounds, if not too pronounced. If there is a possibility of pit becoming deep
enough to penetrate pad, Figure 8A-8, right, reject contact assembly.
Revised: 2/13/89
2D12
CHEROKEE ARROW III SERVICE MANUAL
POWER PLANT - LYCOMING
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