Mercury MerCruiser MCM 454 Mag MPI Service Manual page 346

SERVICE MANUAL NUMBER 23
4. Inspect each plug individually for badly worn electrodes, glazed, broken or blistered
REPLACING
IMPORTANT: Tapered seat spark plugs are not interchangeable with non-tapered
(with gasket) spark plugs. Do not use gaskets on tapered seat plugs.
1. Clean the plug seating area on the cylinder heads. Clean the tapered seat area of each
2. Adjust spark plug gap with a round feeler gauge. Bend side electrode to adjust gap.
IMPORTANT: It is recommended that spark plugs be torqued to the amount specified.
In the absence of a torque wrench or access problems to the plugs, the spark plugs
should be hand tightened until the plug seats on the cylinder head. Then, securely
tighten with appropriate wrench and socket. On tapered seat plugs, only slight rota-
tion (approximately 1/8 or less of a full turn) after seating, is required to create a seal
and secure the plug.
3. Install spark plugs and torque to specifications. Refer to "Torque Specifications," in this
4. Install spark plug wires in proper order. Refer to "Engine Rotation and Firing Order"
Index
90-861326--1 MARCH 1999
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porcelain and replace where necessary.
a - Porcelain Insulator
b - Insulator - Cracks Often Occur at This Point
c - Shell
d - Proper Gap
e - Side Electrode
f - Center Electrode (When Adjusting Gap - DO NOT Bend)
tapered seat spark plug.
Refer to "Specifications" in SECTION 1B, for correct spark plug gap.
a - Seating Area
b - Gap
section.
and/or "Spark Plug Wires," following.
a
b
c
f
d
e
a
b
IGNITION SYSTEM
72734
75084
Page 4B-5