Engine Cylinder Leakdown Test - Polaris General 2020 Service Manual

ENGINE / COOLING SYSTEM

ENGINE CYLINDER LEAKDOWN TEST

OVERVIEW
A cylinder leakdown test used to determine the condition
of the engine by introducing compressed air into the
cylinder and measuring the rate at which it leaks out.
Leakdown primarily tests pistons and rings, valve
sealing, and the head gasket. A cylinder leakdown test is
the most accurate test to examine engine condition.
NOTICE
Leakdown testing is preferred over compression testing
for the following:
• Piston rings take time to seat. Frequently a new
vehicle can have compression below the
specification because of the "Break-In" period and
can cause misdiagnosis.
• Elevation can cause variance in compression
causing compression specifications and testing to be
inaccurate.
• Restricted exhaust or intake can affect compression
and could give a false indication that the engine is
bad.
• Compression specification readings on the low end of
a range can cause technicians to suspect engine
faults and lead to misdiagnosis.
• Even after performing a compression test leakdown
will need to be performed to diagnose the root cause.
IMPORTANT
If a compression test is performed before, or in place of
a leakdown test, the results should always be
compared to other cylinders. If diagnosing an engine
with two or more cylinders, this must be compared to
the adjacent cylinder. If diagnosing a single cylinder
engine, this must be compared to a known good
For any additional information needed for testing refer to
the tester manufacturer's instructions. Never use high
pressure leakage testers as crankshaft seals may
dislodge and leak.
TESTING PROCEDURE
1. Warm up the engine to operating temperature.
2. Remove the spark plug from the cylinder being
tested.
Use caution when removing the spark plug as the
engine will be hot.
3.4
engine.
WARNING
3. Turn the engine over by hand until the piston in that
cylinder is at top dead center (TDC).
NOTICE
If engine is not at TDC when air pressure applied to the
cylinder, the engine will likely turn over. Keeping the
piston at TDC vertically aligns the piston and
connecting rod with the crank
Leaving the remaining spark plugs installed will help
provide some additional resistance to the engine
unintentionally turning over.
Remove any tools used to turn the engine over before
putting air to the cylinder. If the cylinder being tested is
not perfectly on TDC, the engine will likely turn over
quickly and tools can strike you or damage the
machine.
4. Install the gauge's air-fitting adapter into the spark
plug hole and connect air pressure to the inlet side of
the gauge. Remember to double-check that your
gauge reads "zero" before you start.
5. Gradually increase air pressure up to no more than
100 psi. Ensure piston remains at TDC. If engine
turns over, reduce supplied pressure to 0 and rotate
engine to TDC.
6. Record your leak-down percentage for the cylinder
you're testing. Test any remaining cylinders using the
same method.
IMPORTANT
Refer to the manufacturers instructions to calculate the
leak. Some testers may not use a calculation and the
gauge may give you a percent of leak or capacity.
NOTICE
If the same cylinder is tested multiple times without
running the engine can cause variable readings.
Cylinder Leakage Service Limit:
If leakage exceeds service limit, inspect the engine for
the cause.
TROUBLESHOOTING
Test and compare all cylinders before attempting further
repairs. Leak percentage should be consistent between
cylinders. A 5 to 10 percent variance between cylinders
would likely be considered normal.
9850067 R01 - 2020-2021 GENERAL / GENERAL XP Service Manual
CAUTION
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