Pressure Test - Stihl FS 120 Manual

5/20/2018
4.2.2

Pressure Test

- Carry out preparations -
see 4.2.1.
Connect pressure hose of tester
•
1106 850 2905 to nipple on test
flange.
•
Close the vent screw (1) on
the rubber bulb.
- Use rubber bulb to pump air into
the crankcase until the gauge
indicates a pressure of 0.5 bar
(7.25 psi). If this pressure re-
mains constant for at least 20
seconds, the crankcase or de-
compression valve, if fitted, is
airtight.
FS 120, 200, 300, 350, 400, 450, FR 350, 450
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A
V
6
1
0
A
R
0
5
2
However, if the indicated pressu-
•
re 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.
- If the decompression valve is not
airtight, install a new one
4.8.
1
- Repeat the pressure test.
- Carry out the vacuum test -
A
V 4.2.3.
6
4
0
A
R
3
4
- After finishing the test, open the
1
vent screw and disconnect the
hose.
- Remove the test flange.
- Slacken off the muffler mounting
screws.
- Pull out the sealing plate and
tighten down the screws to
8.5 Nm (6.3 lbf.ft).
- Install carburetor -
8.2.2.
4.2.3
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
A
out with the vacuum pump to
V
7
1
0 detect this kind of fault.
A
R
0
5
2
- Carry out preparations -
see 4.2.1.
- see
see
•
Connect the suction hose of
vacuum pump 0000 850 3501
to test flange nipple.
see 8.2.1 or
Close vent screw (1) on
•
pump cylinder.
Operate lever (2) until the gauge
•
(3) indicates a vacuum of 0.5 bar
(7.25 psi).
Vacuum Test
3
1
12/63
A
V
6
1
0
A
R
0
5
2
2
A
V
8
1
0
A
R
0
5
2
11