IO-390-D Series Engine Maintenance Manual
© 2020 Avco Corporation. All Rights Reserved
74-20
March 2020
Page 275
IO-390-D Series Engine Maintenance Manual
9.
Spark Plug Rotation
NOTICE:
As part of routine service, rotate spark plugs in different locations per Table 2 every 100
hours of engine operation or annually (whichever occurs first) or when there is evidence
of spark plug fouling.
A.
Remove all of the spark plugs. Refer to the “Spark Plug Removal” procedure in this chapter.
B.
Examine each spark plug and ignition lead. Refer to the “Spark Plug Inspection” and
“Ignition Harness Inspection” procedures in this chapter.
C.
Complete the “Spark Plug Cleaning” procedure in Chapter 05-30.
CAUTION
USE CARE TO PREVENT THE COPPER-BASED ANTI-SEIZE FROM
GETTING ON THE SPARK PLUG ELECTRODE OR IN THE
COMBUSTION CHAMBER.
DO NOT APPLY A GRAPHITE-BASED COMPOUND TO THE SPARK
PLUG THREADS.
D.
Apply C5-A Copper-Based Anti-Seize (Figure 4) or
engine oil to the threads of each spark plug (starting two
full threads from the electrode.)
E.
Rotate acceptable spark plugs per the rotation scheme in
Table 2.
F.
Refer to the “Spark Plug Installation” procedure in this
chapter.
Figure 4
Copper-Based Anti-Seize
Applied to Spark Plug Threads
Table 2
Spark Plug Rotation Scheme
#1 Top
with
#4 Bottom
#2 Top
with
#3 Bottom
#3 Top
with
#2 Bottom
#4 Top
with
#1 Bottom
10.
Spark Plug Installation
A.
If not already done, apply C5-A Copper-Based Anti-Seize (Figure 4) or engine oil to the
threads of each spark plug (starting two full threads from the electrode.)
CAUTION
FAILURE TO INSTALL A NEW SPARK PLUG GASKET ANY TIME A
SPARK PLUG IS INSTALLED CAN RESULT IN INCOMPLETE
SEALING OF THE COMBUSTION CHAMBER, LOSS OF SPARK PLUG
HEAT TRANSFER, SPARK PLUG OVERHEATING, POSSIBLE
REIGNITION/DETONATION, AND INTERNAL ENGINE DAMAGE.
NEVER INSTALL A SPARK PLUG THAT HAS BEEN DROPPED.
B.
Install a new spark plug gasket (Figure 2) with the spark plug. A new gasket must be installed
whether the spark plug is new or is acceptable and being reused.
