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Recommendations to prevent spark plug fouling:
B.
• If the engine is approved for use with unleaded fuel per the latest revision of Service
Instruction SI-1070, use unleaded fuel after purging the fuel system.
• Rotate top and bottom spark plugs every 100 operating hours or annually – refer to the
"Spark Plug Rotation" procedure in this chapter.
• Operate the engine between 1000 and 1200 rpm after engine start and during warm-up.
(At these speeds the spark plug core temperatures are sufficiently hot to activate the lead
scavenging agents to prevent lead deposits on the spark plugs.)
• Operate the engine at the specified operating temperature to prevent low temperature
operation.
• Use oil cooler baffles to keep the oil temperature from decreasing during winter flight.
• Do not stop the engine immediately after landing to prevent rapid engine cooling.
• Before engine shutdown, operate the engine between 1000 and 1200 rpm until operating
temperatures are stable. Then increase engine speed to 1800 rpm for 15 to 20 seconds.
Then decrease engine speed between 1000 and 1200 rpm before engine shutdown.
6. Spark Plug Port Seal Inspection
NOTICE: This inspection is usually done to complete the check of the Heli-coil
in the cylinder head.
A. Apply a soap solution to the seating area of the cylinder head.
B. Look for bubbles. If bubbles are seen, replace the Heli-coils
spark plug Heli-coil
C. Examine the spark plugs (if not already done). Refer to the section "Spark Plug Inspection"
procedure in this chapter.
D. Examine the surface of the cylinder (covered with soap) for cracks. Refer to the "Visual
Cylinder Inspection Procedure" in Chapter 72-30.
7. Spark Plug Cleaning
Complete the "Spark Plug Cleaning" procedure in Chapter 05-30.
8. Spark Plug Gap Setting
A. Refer to the latest revision of Service Instruction No. 1042 to identify the correct spark plug
for this engine.
B. Make sure the "Spark Plug Cleaning" procedure in Chapter 05-30 was completed and that the
inside of the spark plug barrel is clean and dry and does not have any residue from cleaning.
C. Before spark plug installation, set the spark plug gap in accordance with the latest revision of
Service Instruction No. SI-1042.
D. Reset and test the spark plugs in accordance with the spark plug manufacturer's instructions.
74-20
Page 274
®
inserts with oversize inserts per instructions in Chapter 72-30.
IO-390-D Series Engine Maintenance Manual
IO-390-D Series Engine Maintenance Manual
®
. Replace all loose or damaged
© 2020 Avco Corporation. All Rights Reserved
®
spark plug insert
March 2020
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