Vacuum Test - Stihl 020 T Service Manual

• However, if the indicated pressure
drops, the leak must be located and
the faulty part replaced.
Note: To find the leak, coat the
suspect area with oil and
pressurize the crankcase again.
Bubbles will appear if a leak exists.
• Carry out the vacuum test –
see 4.2.3.
• After finishing the test, open the
vent screw and disconnect the
hose.
• Remove the test flange and refit
the carburetor - see 10.2.
• Remove the flange and sealing
plate.
• Install the muffler - see 4.1.
STIHL 020 T
4.2.3

Vacuum Test

Oil seals tend to fail when sub-
jected to a vacuum, i.e. the sealing
lip lifts away from the crankshaft
during the piston's induction stroke
because there is no internal
counterpressure.
An additional test can be carried
out with the vacuum pump to
detect this kind of fault.
The preparations for this test are
the same as for the pressure test –
see 4.2.1.
• Connect the vacuum pump's suction
hose to test flange nipple.
• Make sure spark plug is tight.
• Pull out the pump piston several
times until the gauge indicates a
vacuum of 0.5 bar (7.25 psi).
Note: When you release the pump
piston, the non-return valve auto-
matically seals the suction hose.
If the vacuum reading remains
constant, or rises to no more than
0.4 bar (5.8 psi) within 20 seconds,
it can be assumed that the oil seals
are in good condition.
However, if the pressure continues
to rise (reduced vacuum in the
crankcase), the oil seals must be
replaced, even if no leaks were
detected in the pressure test.
• Remove the test flange and refit
the carburetor - see 10.2.
• Remove the flange and sealing
plate.
• Install the muffler - see 4.1.
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