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MAINTENANCE
2.18
COMPRESSION TEST
NOTE: 4-Stroke 500 and 425 engines are equipped
with an automatic decompressor. Compression
readings will vary in proportion to cranking speed
during the test. Average compression (measured) is
about 50-90 psi
during a compression test.
Smooth idle generally indicates good compression.
Low engine compression is rarely a factor in running
condition problems above idle speed. Abnormally
high compression can be caused by a decompressor
malfunction, or worn or damaged exhaust cam lobes.
Inspect camshaft and automatic decompression
mechanism if compression is abnormally high.
A cylinder leakage test is the best indication of engine
condition on models with automatic decompression.
Follow manufacturer’s instructions to perform a
cylinder leakage test. (Never use high pressure
leakage tester as crankshaft seals may dislodge and
leak).
Cylinder Compression
Standard 50-90 PSI
Cylinder Leakage
Service Limit 10 %
(Inspect for cause if leakage exceeds 10%)
ENGINE MOUNTS
Inspect rubber engine mounts (A) for cracks or
damage. Check engine fasteners and ensure they
are
tight.
A
A
A
SPARK PLUG
1. Remove spark plug high tension lead. Clean plug
area so no dirt and debris can fall into engine
when plug is removed.
2. Remove spark plug.
3. Inspect electrodes for wear and carbon buildup.
Look for a sharp outer edge with no rounding or
erosion of the electrodes.
4. Clean with electrical contact cleaner or a glass
bead spark plug cleaner only. CAUTION: A wire
brush or coated abrasive should not be used.
5. Measure gap with a wire gauge. Refer to
specifications for proper spark plug type and gap.
Adjust gap if necessary by bending the side
electrode carefully. (Ill. 1)
6. If necessary, replace spark plug with proper type.
CAUTION: Severe engine damage may occur if
the incorrect spark plug is used.
7. Apply a small amount of anti-seize compound to
the spark plug threads.
8. Install spark plug and torque to specification.
Recommended Spark Plug:
NGK BKR5E
Spark Plug Torque:
14 Ft. Lbs. (19 Nm)
.036″ (0.9 mm)
Spark Plug Gap