STIHL 019 T
17
4.4.3
Vacuum Test
(for diaphragm)
In these chainsaws the fuel-air
mixture is sucked into the crankcase
via a diaphragm valve. This valve
closes to prevent the gas mixture
flowing back into the carburetor.
If the diaphragm seating face on the
spacer flange is dirty or the
diaphragm is fatigued or faulty, the
mixture may flow back and result in
an irregular running behavior.
A 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 4.4.1.
4.4.4
Vacuum Test
(for oil seal)
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.
• Close the vent screw (1) on the
pump.
• Operate lever (2) until pressure
gauge (3) indicates a vacuum of 0.4
bar (5.8 psi).
Note:
If the vacuum reading remains
constant, or rises to no more than
0.3 bar (4.25 psi) within 20 seconds,
it can be assumed that the spacer
flange and the diaphragm are in good
condition. However, if the pressure
continues to rise, the spacer flange or
the diaphragm must be replaced.
- After finishing the test, open the vent
screw.
- Carry out vacuum test for oil seals
• Take out the screws (1).
• Remove the test flange (2) and
gasket.
• Take out the screws (1).
• Remove the spacer flange (2)
and gasket.
• Connect suction hose of vacuum
pump 0000 850 3501 to test flange
nipple.
