Stihl 088 - Vacuum Test

STIHL 088 18
4.2.3
V
acuum Test
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 4.2.2.
Note: !f 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 oil seals are in
good condition.
However, if the pressure continues to
rise (reduced vacuum in the
crankcase), the oil seals must be
replaced.
- After finishing the test, open the
vent screw and disconnect the
hose.
- Remove the test flange.
- Install the carburetor
- see 10.2.1.
- Remove the test flange with clamp.
- Install the muffler - see 4.1.
- Unscrew the plug from the cylinder.
- Install decompression valve
- see 4.8.
• 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.
- Install the carburetor - see 10.2.1.
- Remove the test flange with clamp.
- Install the muffler - see 4.1.
- Unscrew the plug from the cylinder.
- Install decompression valve see 4.8.
• 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).
• Connect suction hose of vacuum
pump 0000 850 3501 to test
flange nipple.