Vanguard
TM
Twin-Cylinder OHV Liquid-Cooled Engine
Section 2 - Troubleshooting
Page 20
5. Pull the regulator adjustment knob out and
turn knob counterclockwise as far as it will go, Fig.
23. Make sure air outlet valve is closed.
Fig. 23
6. Connect the tester to the shop air source
(minimum air pressure of 70 psi).
7. Install the outlet hose into the spark plug hole of
the cylinder being tested. Be sure “O” Ring is
seated to prevent air leak at spark plug hole.
Connect other end to tester.
8. Turn regulator adjustment knob clockwise until the
tester’s needle is on the set point. Push knob in to
lock. Slowly open air outlet valve and note
position of needle on gauge, Fig. 24.
Fig. 24
NOTE: Any air leaks at the connections or
fittings of the tester will affect the accuracy of the
test.
9. Listen for air leaking from the cylinder head
gasket, carburetor, exhaust system and the
crankcase breather tube.
NOTE: If a high flow of air is leaking from the
exhaust and carburetor, make sure the piston is
at TDC on the compression stroke.
a. Air flowing between the cylinder and cylinder
head indicates that the cylinder head gasket is
leaking.
b. Air flowing from the carburetor indicates air is
leaking past the intake valve and seat.
c. Air flowing from the exhaust system indicates
air is leaking past the exhaust valve and seat.
d. Air flowing from the crankcase breather tube
or high oil fill dipstick tube indicates air is
leaking past the piston rings.
10. When test is complete, close air valve. Then, pull
out knob and turn counterclockwise as far as it will
go to release pressure in combustion chamber.
Reading is Green. A small
amount of air is leaking
from head gasket.
Reading is Green.
Minimum air leakage.
Reading is Yellow/Red or
Red, and all the air is
leaking from one
component.
Reading is Red, and air is
leaking from several
components.
Replace head gasket, and
re-test.
Look for problems tat are
not compression related.
Look for a possible
problem with that
component.
Check that piston is at
TDC on the compression
stroke. If reading does
not change, look for
problems beginning with
the component that
appeared to leak the
most air. Re-test after
repair.
COMPRESSION TEST RESULTS
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