Vacuum Test - Stihl 4141 Series Manual

5.3.2

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 counter-
pressure.
A test with the vacuum pump
0000 850 3501 is carried out to
detect this kind of fault.
1
2
Connect suction hose of the
vacuum pump (2) 0000 850 3501
to the nipple on the test flange
(1).
3
1
Close vent screw (1) on pump
cylinder.
Operate lever (2) until the gauge
(3) indicates a vacuum of 0.5 bar
(7.25 psi).
Series 4141 Powerhead
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 oil seals
are in good condition.
1
However, if the pressure
continues to rise (reduced
vacuum), replace the oil seals,
impulse hoses (1) and/or the
diaphragm carriers (2) on the
right and left of the cylinder.
2
In order to exclude the influence
of the impulse hoses on the
leakage test, use hose (2)
4203 708 9506 to connect the
two diaphragm carriers (1)
together. Repeat the test with this
setup.
If a leak is still indicated, check for
damage in the area of the cylinder/
oil seals.
If the leak no longer exists, look for
defect in the area of the diaphragm
carriers/impulse hoses.
– Check impulse hoses for damage
or porosity and replace if
necessary.
– Repeat the leakage tests after
finishing repairs.
– Remove the test flange.
– Install impulse hoses, paying
attention to the markings on the
hoses:
F = flywheel side
1 2
S = starter side
– Install the carburetor and air filter.
– Loosen muffler mounting screws
and remove the sealing plate.
Tighten the screws to 8 Nm
(5.9 lbf.ft).
Reassemble in the reverse
sequence.
2
1
13