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STIHL 029, 039
26
4.2.3
Vacuum Test
Tester's suction hose connected
to nipple on test flange
Pressure-testing the engine
- Remove the test flange and refit
the carburetor - see 11.2.
- Remove the flange and sealing
plate.
- Refit the muffler - see 4.1.
However, if the indicated pressure
drops, the leak must be located and
the faulty part replaced.
Note:
Coat
the suspect area with oil and
pressurize the engine housing
again. Bubbles will appear if there is
a leak in the oiled area.
- Carry out the vacuum test - see
- After finishing the tests, open the
vent screw and disconnect the
hose.
Oil seals tend to fail when subjected
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.
- Pull out the pump piston several
times until the gauge indicates a
vacuum of 0.4 bar (5.8 psi).