(TCM
IGNITION SYSTEM)
74-00-00
GENERAL
Conventional dual ignition is provided by two magnetos. The left magneto fires 1-3-5 lower
and
2-4-6 upper spark plugs, while the right magneto fires the 1-3-5 upper and
2-4-6
lower
spark plugs.
The TCM S-20 Series Magneto is designed to provide ignition for six cylinder aircraft engines.
The magnetos generate and distribute high tension pulses through high tension leads to the
spark plugs. Overhaul is recommended at engine overhaul or at the expiration of four years
without regard to engine operating hours, whichever comes first.
To obtain the retard spark necessary for starting, the magnetos employ an impulse coupling.
The purpose of the impulse coupling is to: (1) rotate the magnet between impulse trips faster
than engine cranking speed thus generating a better spark for starting the engine, (2)
automatically retard the spark during engine cranking, and
(3)
act as a drive coupling for the
magneto.
The following detailed explanation gives the meaning of the various letters and numbers
appearing in the type designations:
A.
"S
indicates single type ignition unit.
8.
"6"
indicates number of cylinders fired.
C. "R" or
"C'
indicates direction of rotation of rotating magnet viewed from drive end; "R"
for right-hand,
"L"
for left-hand.
D.
"N" indicates manufactured by TCM.
E.
The dash number (such as -25) indicates a certain execution of the basic type magneto.
74-00-01
MAGNETO INSTALLATION
Refer to Service Bulletin
M-88-8R1,
or
current revision as applicable.
Insure that magneto is proper part number for engine installation. Insure that internal timing
of magneto is correct as per TCM form no. L-250-10 (or latest revision) for S-20 series
magneto. This publication is included in TCM
Ignition Systems Master Service Manual Form
No.
X40000 (Printed Edition) or Form No. X40000F (Microfiche Edition).
Remove timing inspection window plug from top of magneto.
C4UTION
.
. .
When installing a
TCM
magneto on the engine, a gear holding timing device
should
nut
be used,
as
hidden gear tooth damage
may
result.
Turn engine crankshaft until piston in the No.
1
cylinder is at its full advance firing position.
Rotate the magneto shaft in its normal direction of rotation until the painted chamfered tooth
of the distributor gear is centered in the inspection window. Install magneto on engine. Do
not tighten magneto
holddown bolts.
Fabricate P-lead adapter using appropriate terminal
kit
and a length of wire. Install adapter
lead on switch terminal of magneto. Connect positive lead of TCM 11-9110-1 timing light, or
equivalent, to bare end of adapter. Connect common lead of timing light to a good ground.
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