Stihl MS 171 Manual page 31

8.2.2 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.
: Connect suction hose (1) of
pump 0000 850 1300 to
nipple (arrow).
1
: Push ring (1) to the left.
: Operate the lever (2) until the
pressure gauge (arrow) indicates
a vacuum of 0.5 bar.
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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 8.3
– After finishing the test, push the
ring to the right to vent the pump.
– Continue with pressure test,
b 8.2.3
1
8.2.3 Pressure Test
Carry out the same preparations as
for the vacuum test, b 8.2.2
– Always carry out the vacuum test
before the pressure test, b 8.2.2
2
: Connect pressure hose (1) of
pump 0000 850 1300 to nipple
(arrow).
1
: Push the ring (1) to the right.
: Operate the lever (2) until the
pressure gauge (arrow) indicates
a pressure of 0.5 bar. If this
pressure remains constant for at
least 20 seconds, the engine is
airtight.
1
– 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. 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 test flange.
– Install the carburetor, b 14.3
– Loosen the muffler and remove
the sealing plate.
– Tighten down the muffler firmly.
– Reassemble all other parts in the
reverse sequence.
– Tightening torques, b 3.5
MS 171, MS 181, MS 211
2