Vanguard BIG BLOCK M540000, Repair Manual, Page: 18 / 168

Clean/Gap/Replace Spark Plug
1. Remove spark plug wire from spark plug terminal.
2. Thoroughly clean area around spark plug to keep dirt and
debris out of combustion chamber.
3. Remove spark plug from cylinder head using a 5/8 inch
spark plug wrench.
4. Check condition of threads in cylinder head. If necessary,
soften deposits with penetrating oil and clean out with a
thread chaser.
5. Clean spark plug using a wire brush and commercial
solvent. Do not bead blast spark plug. Obtain new spark
plug if electrode is pitted, burned, worn down or worn
unevenly. Inspect porcelain for cracks and damage.
6. Using a feeler gauge ( B , Figure 11), verify spark plug
gap ( A ) is 0.030 in (0.76 mm) for gasoline-fueled engines
and 0.020 in (0.51 mm) for gaseous-fueled engines.
If necessary, adjust gap by carefully bending ground
electrode.
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7. Finger tighten spark plug into cylinder head, and then
tighten to 170 lb-in (19.2 Nm).
8. Install spark plug wire onto spark plug terminal.
Clean/Inspect Muffler
1. Remove spark plug wires from spark plug terminals.
Secure spark plug wires to prevent contact with spark
plug terminal.
2. Remove the oxygen sensor ( A , Figure 12) from the
muffler. Take care to avoid damaging the sensor wires.
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3. Remove the 2 fasteners ( B ) to release heat shield ( C )
from muffler.
4. Clean area around and behind muffler. Proceed as
follows:
A. Remove all loose debris by hand.
B. Remove dust and dirt with a soft bristle brush and a
portable hand held vacuum.
C. Gently scrape away stubborn accumulations of dirt
and other deposits using a plastic putty knife or stiff
bristle brush.
D. Apply a light solvent to bristle brush to loosen and
remove grit and oily residue, if necessary.
5. Inspect muffler for holes, split seams, cracked welds,
loose internal parts, corrosion, and other damage.
Replace as necessary.
6. Inspect muffler manifold and mounting flanges for
cracked welds, breakage, and other damage. Replace as
necessary.
7. Install the heat shield on to the muffler and install the 2
heat shield fasteners. Tighten fasteners to 87 lb-in (9.8
Nm).
8. Install the oxygen sensor ( A ) onto the muffler. Tighten to
160 lb-in (18 Nm).
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