Lycoming IO-390-D Series Maintenance Manual page 256

NOTICE: Always install a larger oversized 0.010 in. (0.254 mm) Heli-Coil
plug hole on the cylinder head to replace a standard sized Heli-Coil
replace a standard sized Heli-Coil
The oversize Heli-Coil
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Coil insert as shown Figure 41.
(1) Disable all power to the engine to prevent propeller rotation and engine start. Disconnect
ignition leads from all spark plugs.
(2) If not already done, remove and discard the Heli-Coil
(3) Apply of coat of grease liberally to the oversize tap.
(4) If the Heli-Coil
precautions to prevent metal shavings from falling into the combustion chamber.
CAUTION
(5) Turn the crankshaft to the start of the compression stroke.
(6) Put 8 ft. (2.4 m) of 3/8 in. (9.5 mm) nylon rope through the opposite spark plug hole.
(7) Turn the crankshaft to force the rope against the bottom of the spark plug hole that is to
be tapped.
(8) Use the 0.010 in. oversize tap, to drill a larger oversize hole for the oversize insert.
(9) Install the new oversize 0.010 in. Heli-Coil
41.
(10) Remove all chips and shavings to prevent contamination from foreign object debris.
(11) Remove the rope from the spark plug hole.
(12) Record replacement, in the engine logbook, of the standard sized Heli-Coil
a new oversized Heli-Coil
72-30
Page 230
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inserts are identified by three marks on the tang of the Heli-
Figure 41
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Heli-Coil Inserts for Long Reach Spark Plugs
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insert is replaced while the cylinder is installed on the engine, take
IF METAL SHAVINGS FALL INTO THE COMBUSTION CHAMBER
OF THE CYLINDER, STOP AND REMOVE ALL SHAVINGS AND
DEBRIS. THE COMBUSTION CHAMBER MUST BE CLEAN.
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insert for the applicable cylinder number.
IO-390-D Series Engine Maintenance Manual
IO-390-D Series Engine Maintenance Manual
insert with another standard sized Heli-Coil
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insert from the spark plug hole.
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insert in the spark plug hole. Refer to Figure
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insert in the spark
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insert. Never
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insert.
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insert with
March 2020