Internal Timing - Dual Magneto - Lycoming O-320 76 Series Operator's Manual

SECTION 5
MAINTENANCE PROCEDURES
(6) Observe that at this time the built in pointer just ahead of the rotor viewing window aligns with the
R or L mark on the rotor depending on whether the magneto is of right or left hand rotation as
specified on the magneto nameplate.
(7) Hold the magneto in its No. 1 firing position (tooth in window center and pointer over R or L
mark on rotor) and install magneto to the engine and loosely clamp in position.
(8) Attach red lead from the timing light to left switch adapter lead, green lead of timing light to right
switch adapter lead and the black lead of the light to magneto housing.
(9) Turn the entire magneto in direction of rotor rotation until the red timing light comes on.
(10) Rotate the magneto in the opposite direction until the red light just goes off indicating left main
breaker has opened. Then evenly tighten the magneto mounting clamps.
(11) Back the engine up approximately 10° and then carefully "bump" the crankshaft in direction of
rotation, at the same time observing the timing lights.
(12) At the No. 1 firing position of the engine, the red light should go off indicating left main breaker
opening. The right main breaker monitored by the green light, must open within ± 2 engine
degrees of the No. 1 firing position.
(13) Repeat steps (9) thru (11) until the condition described in paragraph (12) is obtained.
(14) Complete tightening of the magneto securing clamps by torqueing to 150 in.-lbs.
(15) Recheck timing once more and if satisfactory disconnect timing light. Remove adapter leads.
(16) Reinstall plugs in timing inspection holes and torque 12-15 in.-lbs.
(17) Install the harness leads as shown in Figure 5-1 to spark plug and connect switch lead to proper
terminal.
Some timing lights operate in the reverse manner as described. The light comes on when the
breaker points open. Check you timing light instructions.
d. Internal Timing – Dual Magneto – Check the magneto internal timing and breaker synchronization in
the following manner.
(1) Main Breakers – Connect the timing light negative lead to any unpainted surface of the magneto.
Connect one positive lead to the left main breaker terminal and the second positive lead to the
right main breaker terminal.
(2) Back the engine up a few degrees and again bump forward toward number one cylinder firing
position while observing timing lights. Both lights should go out to indicate opening of the main
breakers, when the timing pointer is indicating within the width of the "L" or "R" mark. If breaker
timing is incorrect, loosen breaker screws and correct. Retorque breaker screws to 20 to 25 in.-lbs.
5-2
LYCOMING SERIES OPERATOR'S MANUAL
NOTE
O-320-H