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YO-233-B2A Engine Maintenance Manual
TEO-540-A1A Engine Maintenance Manual
F. To be acceptable, the spark plug must not have any of the following defects:
(1) Fine wire plugs with loose center or ground electrodes.
(2) Electrodes show signs of metal or impact change.
(3) Massive electrode plugs with copper run-out of center electrode.
(4) Ceramic core nose with a cracked or crazed surface.
G. Measure the spark plug gap to make sure it is at correct tolerance. Reset the spark plug gap if
it is not correct. Refer to the "Set Spark Plug Gap" procedure in this chapter.
4. Spark Plug Fouling
Spark plug fouling can be caused by lead in fuel. Lead deposits can collect on the spark plug
A.
electrodes when the engine operates at lower-than-specified temperatures with fuel rich
mixtures which does not enable vaporization of lead in the aviation gas. These deposits can
cause misfiring.
Recommendations to prevent spark plug fouling:
B.
— Rotate top and bottom spark plugs every 50 operating hours
— 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 and exhaust valve stems.)
— 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 do low power altitude changes or low power landing approaches to prevent rapid
engine cool down.
— 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.
5. Spark Plug Port Seal Inspection
NOTICE: This inspection is usually done to complete the check of the Heli-coil.
Apply a soap solution to the seating area of the cylinder head.
A.
Look for bubbles. If bubbles are seen, replace the Heli-coils. Replace all loose or damaged
B.
spark plug Heli-coil inserts with oversize inserts.
Examine the spark plugs (if not already done). Refer to the section "Examine Spark Plug and
C.
Ignition Leads" procedure in this chapter.
Examine the surface of the cylinder (covered with soap) for cracks. Refer to the "Visual
D.
Cylinder Inspection Procedure" in Chapter 72-30.
© 2021 Avco Corporation. All Rights Reserved
February 2021
74-20
Page 165
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