IO-390-D Series Engine Maintenance Manual
© 2020 Avco Corporation. All Rights Reserved
74-30
March 2020
Page 285
IO-390-D Series Engine Maintenance Manual
B.
Remove the nut and lock washer from the condenser terminal on the magneto. Disconnect
the P-Leads from the magneto. Discard the lock washer.
C.
Remove one of the spark plugs from Cylinder No. 1 per the “Spark Plug Removal”
procedure in Chapter 74-20.
NOTICE:
If the engine is equipped with impulse-coupled magnetos, turn the crankshaft in
the direction of normal rotation until Cylinder No. 1 is at Top Dead Center
(TDC). Continue to turn the crankshaft, in the direction of normal rotation, until
the impulse couplings in the magnetos have snapped and released. Then, turn the
crankshaft in the direction
opposite
normal rotation until Cylinder No. 1 is on
the compression stroke, approximately 35° before TDC.
D.
Turn the crankshaft in the direction of normal rotation until Cylinder No. 1 is on the
compression stroke, approximately 35° before TDC.
E.
Put your thumb over the spark plug hole and turn the crankshaft in the direction of normal
rotation until there is pushback pressure at the spark plug hole.
NOTICE:
Some timing lights operate in the reverse manner than identified herein. The
light comes on when the contact points open. Refer to your timing light
instructions.
F.
Connect the timing light leads to the appropriate magneto condenser terminals and the
ground lead to any unpainted portion of the engine.
NOTICE:
There are two reference points on the engine to be used when aligning the timing
marks on the starter ring gear support:
•
When viewing the starter ring gear support from the crankcase side, the
reference point is the crankcase parting flange (Figure 8).
•
When viewing the starter ring gear support from the propeller side, the
reference point is the timing mark on the starter (Figure 9).
Figure 8
Timing Marks on the Crankcase Side of the
Starter Ring Gear Support Aligned with the
Crankcase Parting Flange
Figure 9
Timing Marks on the Propeller Side of the
Starter Ring Gear Support Aligned with the
Timing Mark on the Starter
