Cessna 170, Service Manual

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Cessna 170 Service Manual
Electrical System
10
cleaning. Be certain to clean the points when finished with electronics cleaner or alcohol (NOT rubbing
alcohol which may contain glycerin.)
REMEMBER: The single most overlooked solution to generator/regulator problems is lack of proper
polarization, followed by improper grounds. Disconnect your battery before working on electrical circuits and
re-polarize the system after re-connection EVERY TIME.
ENGINE STARTER. The electric starter is mounted to the upper rear of the engine accessory case and is
mechanically engaged to the crankshaft gear through a starter adaptor. The starter adaptor consists of a
reduction gear (resembling a large and a small gear fixed to each other) mounted on a sliding gear-shaft.
The reduction gear incorporates a clutch mechanism that provides one-way impetus when turned by the
starter motor. This helps prevent a running engine from damaging the starter by turning it to an overspeed
condition.
When the cockpit starter handle is pulled the associated Bowden cable pulls a starter adaptor lever which in
turn forces the starter adaptor gear-shaft forward into the engine gear case. When the starter adaptor
reduction gear has meshed with the crankshaft gear, the lever comes against the starters integral mounted
electric switch. Further action of pulling the cockpit starter handle forces the lever to activate the starter
switch thereby placing battery current at the disposal of the starter motor. The starter motor rotation drives
rollers within the clutch to lock the reduction gears to each other, and with the reduction gear meshed with
the crankshaft gear the engine crankshaft is thereby turned over for starting.
STARTER ELECTRICAL CIRCUIT
. The starter receives its electrical power at its integrally mounted
switch. This starter switch receives this power directly from the battery solenoid only after the solenoid is
activated by the cockpit master switch, however the starter motor itself is not energized until that integral
switch is depressed/activated via the cockpit starter handle cable and the starter adaptor lever. (Note: Two
wires are connected to the starter integral switch terminal. One is the large (#4 gauge minimum) power
supply cable from the battery solenoid. The other is a 10 or 8 gauge wire that brings electrical power directly
to the cockpit main electrical buss. It is merely using the starter switch terminal as a source of electrical
power, since that terminal is energized whenever the battery solenoid is activated by the cockpit master
switch. )
STARTER LEVER AND BOWDEN CABLE ADJUSTMENT . The starting lever should have a minimum
amount of free-play before it’s lower end contacts the sliding pinion shaft of the starter adaptor. The lever
should move the pinion shaft a minimum of 7/16” into the engine accessory case before the adjusting stud at
the levers upper end contacts the starter switch button. See Appdx. EL, FIG 10.
When the cockpit starter pull-knob is released, it should decisively return to the forward position thereby
releasing the starter lever from contact with the pinion shaft. If this does not occur, then the cable should be
repaired/replaced and/or the lever return spring at the top of the lever replaced/adjusted. Note: Some
aircraft are not equipped with this optional return spring. It may be added to all aircraft with pull starters.
AIRCRAFT LIGHTING SYSTEM.
Lighting equipment consists of landing and taxi lights, navigation lights, interior and instrument panel lights,
courtesy lights and on some aircraft, a rotating beacon and/or anti-collision light system.
LANDING AND TAXI LIGHTS.
The landing and taxi lights are mounted in the leading edge of the left wing.
They are PAR-36, 100-Watt GE-4509 bulbs. A clear plastic cover provides weather protection for the lamps
and is shaped to maintain the leading edge curvature of the wing. The landing lamp is mounted on the
inboard side and adjusted to throw its beam further forward than the taxi light. A single switch controls both
lights. The lamps point of aim may be adjusted by movement of four (each) adjusting screws. Preliminary
adjustment specifications are found in Appdx..-EL.
REMOVAL AND REPLACEMENT OF TAXI/LANDING LIGHT.
a. Remove the 18 screws securing the landing light cover and remove the cover and its retainer strip.
b. Two channels hold lamps to the wing bracket. One must be removed by removing at least
two screws. (Note the number of turns each screw requires for its removal. This is
important in order not to shift the point of aim of each light)
c. Remove the two brass screws attaching the wires to the lamp. (Polarity is not important.)
d. Attach the wiring to the new lamps using their supplied brass screws/toothed washers.