Stihl MS 311 User Manual - Page 30

Vacuum Test, Pressure Test - 20 bar

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2 4 3 2 3 1 4903RA239 TG 4903RA238 TG 4903RA225 TG 1 2 1 : Check that the sleeve (1) and washer (2) are in place. 2 1 2 - Line up the flange (1) 1140 890 1200 and fit it over the studs : Fit the test flange (1) 1140 890 1200. 4903RA237 TG : Connect suction hose (1) of pump 0000 850 1300 to the nipple (arrow). : Push ring (2) to the left. : Operate the lever (3) until the pressure gauge (4) indicates a vacuum of 0.5 bar. If the vacuum reading remains constant, or rises to no more than 0.3 bar 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 engine), the oil seals must be replaced, b 6.3. - After finishing the test, push the ring to the right to vent the pump. : Push ring (1) to the right. : Operate the lever (2) until the pressure gauge (3) indicates a pressure of 0.5 bar. If this pressure remains constant for at least 20 seconds, the engine housing is airtight. - If the pressure drops, the leak must be located and the faulty part replaced. To find the leak, coat the suspect area with oil and pressurize the engine housing again. Bubbles will appear if a leak exists. - After finishing the test, push the ring to the left to vent the pump - disconnect the hose. : Fit the nuts (2) and tighten them down firmly. 6.2.2 Vacuum 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. A test can be carried out with pump 0000 850 1300 to detect this kind of fault. - Continue with pressure test, b 6.2.3 6.2.3 Pressure Test Carry out the same preparations as for the vacuum test, b 6.2.2 - Remove the flange. - Loosen the screws on the muffler and pull out the sealing plate. - Tighten down muffler screws firmly and fit new plugs. - Install the carburetor, b 12.5 - Reassemble all other parts in the reverse sequence. MS 311, MS 391 29

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29
MS 311, MS 391
:
Check that the sleeve (1) and
washer (2) are in place.
–
Line up the flange (1)
1140 890 1200 and fit it over the
studs
:
Fit the test flange (1)
1140 890 1200.
:
Fit the nuts (2) and tighten them
down firmly.
6.2.2
Vacuum 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.
A test can be carried out with pump
0000 850 1300 to detect this kind of
fault.
4903RA225 TG
1
2
4903RA237 TG
2
2
1
:
Connect suction hose (1) of
pump 0000 850 1300 to the
nipple (arrow).
:
Push ring (2) to the left.
:
Operate the lever (3) until the
pressure gauge (4) indicates a
vacuum of 0.5 bar.
If the vacuum reading remains
constant, or rises to no more than
0.3 bar 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 engine), the oil seals
must be replaced,
b
6.3.
–
After finishing the test, push the
ring to the right to vent the pump.
–
Continue with pressure test,
b
6.2.3
6.2.3
Pressure Test
Carry out the same preparations as
for the vacuum test,
b
6.2.2
4903RA238 TG
3
2
4
1
:
Push ring (1) to the right.
:
Operate the lever (2) until the
pressure gauge (3) indicates a
pressure of 0.5 bar. If this
pressure remains constant for at
least 20 seconds, the engine
housing is airtight.
–
If the pressure drops, the leak
must be located and the faulty
part replaced.
To find the leak, coat the suspect
area with oil and pressurize the
engine housing again. Bubbles will
appear if a leak exists.
–
After finishing the test, push the
ring to the left to vent the pump –
disconnect the hose.
–
Remove the flange.
–
Loosen the screws on the muffler
and pull out the sealing plate.
–
Tighten down muffler screws
firmly and fit new plugs.
–
Install the carburetor,
b
12.5
–
Reassemble all other parts in the
reverse sequence.
4903RA239 TG
1
2
3