3.4
Section 3
Troubleshooting
Leakdown Test Results
Air escaping from crankcase breather .......................................................Rings or cylinder worn.
Air escaping from exhaust system .............................................................Defective exhaust valve/improper seating.
Air escaping from carburetor ......................................................................Defective intake valve/improper seating.
Gauge reading in Low (green) zone ...........................................................Piston rings and cylinder in good
condition.
Gauge reading in Moderate (yellow) zone ...............................................Engine is still usable, but there is some
wear present. Customer should start
planning for overhaul or replacement.
Gauge reading in High (red) zone .............................................................Rings and/or cylinder have considerable
wear. Engine should be reconditioned or
replaced.
If the fl ywheel end is more accessible, use a
breaker bar and socket on the fl ywheel nut/screw
to hold it in position. An assistant may be needed
to hold the breaker bar during testing. If the
engine is mounted in a piece of equipment, it may
be possible to hold it by clamping or wedging a
driven component. Just be certain that the engine
cannot rotate off of TDC in either direction.
4. Install the adapter into the spark plug hole, but
do not a ach it to the tester at this time.
5. Connect an air source of at least 50 psi to the
tester.
6. Turn the regulator knob in the increase direction
(clockwise) until the gauge needle is in the yellow
Set area at the low end of the scale.
7. Connect the tester quick-disconnect to the adapter
hose while fi rmly holding the engine at TDC.
Note the gauge reading and listen for escaping
air at the carburetor intake, exhaust outlet, and
crankcase breather.
8. Check the test results against the following table:
Compression Test
A compression test is best performed on a warm
engine. Clean any dirt or debris away from the base of
the spark plug before removing it. Be sure the choke
is off , and the thro le is wide open during the test.
Compression should be at least
45 psi
.
Cylinder Leakdown Test
A cylinder leakdown test can be a valuable alternative
to a compression test. By pressurizing the combustion
chamber from an external air source, you can
determine if the valves or rings are leaking and how
badly.
The Cylinder Leakdown Tester (refer to Section 2) is
a relatively simple, inexpensive leakdown tester for
small engines. The tester includes a quick disconnect
for a aching the adapter hose, and a holding tool.
Leakdown Test Instructions
1. Run the engine for 3-5 minutes to warm it up.
2. Remove the spark plug and the air fi lter from
engine.
3. Rotate the cranksha until the piston (of
cylinder being tested) is at top dead center of
the compression stroke. Hold the engine in this
position while testing. The holding tool supplied
with the tester can be used if the PTO end of
the cranksha is accessible. Lock the holding
tool onto the cranksha . Install a 3/8 in. breaker
bar into the hole/slot of the holding tool, so it
is perpendicular to both the holding tool and
cranksha PTO.
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