Mechanical Checks; Electrical Checks - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
a.
MECHANICAL CHECKS (PA-31-350, S/N 31-5001 and up): Inspect the short tach cables used
to drive the pulse generator, strobe sensor (or other pulse generator in later models) and related components
for the following conditions:
1.
Insufficient lubrication. Lubricate with a suitable High Temperature Grease.
2.
The retainer clip on the drive end of the tach cable is not chafing against the bell housing. No
signs of chafing should be evident.
3.
The square ends of the tach cable is fraying. If so, dip the end in silver solder or braze it. Then
file the end square to fit mating unit core.
4.
Be certain the core of the pulse generator and strobe sensor (or other pulse generator in later
models) rotates when the propeller is turned.
5.
Check the dual drive units for possible broken parts.
6.
Check the engine drive pad for possible damage.
7.
Check tachometer shaft core (engine to strobe sensor) to assure that core has 7/16 inch minimum end
play. Tachometer shaft core may be cut as required at output (square) end. Too much end play may cause cable core to
bind in the housing.
b.
ELECTRICAL CHECKS: (PA-31-350, S/N 31-5001 thru 31-7852037): Perform the following checks to
isolate any trouble in the electrical components of the system.
NOTE
To perform some of the following checks will require a standard
multimeter with a 50 volt AC scale and/or other test equipment
which can be fabricated from easily obtainable components. It is
advisable to make the connecting cables long enough to extend
into the cockpit.
I. Pulse generator, glow lamps and wire harness checks:
(a)
Ascertain that all tach shafts are in position and rotate the pulse generator and strobe
sensor with rotation of the respective engines.
(b) Start and run master engine at near cruise RPM. Set selector switch at Prop Sync.
(c) Disconnect plug PL3 at the strobe sensor and measure AC voltage at Pins D to ground
coming from the computer.
(d)
Measure AC voltage at Pin E to ground coming from the computer.
(e)
These open circuit readings should be from 30 to 40 volts AC.
NOTE
The pulse generator may be removed and checked with the use of an
electric drill or air motor regulated to limit the RPM to 1750. Drive
the generator from the tang end of the core. A patch cable junction
box may be fabricated to simplify the following checks. (Refer to
Figure 14-55.)
Reissued: 9/23/80
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