Testing With Excess; Pressure; Testing With Negative - Stihl TS 400 Manual

STIHL TS 400
- The leak must be located and the
defective part replaced if the
pressure drops.
Note: Coat the supposedly
defective area with oil and
pressurize the crankcase again.
Bubbles form in the oil-coated
area if defective.
- Then test under vacuum as
described in chapter 5.2.3.
- After testing, open venting screw
and remove hose.
- Remove test flange and install
carburetor, see chapter 10.2.2.
- Unscrew muffler screws.
- Draw out sealing plate.
- Tighten muffler screws with a
torque of 10.0 Nm.
- Fit shroud, see chapter 5.5.
5.2.3 Testing with
negative pressure
The rotary shaft seals usually fail in
the presence of a negative pressure.
Due to the absence of an inner
counterpressure, the sealing lip lifts
off the crankshaft during the piston's
induction stroke.
This defect can be identified by
additional testing with a vacuum
pump. The preparatory steps for
this test are the same as when
testing with excess pressure as
described in chapter 5.2.1.
• Connect the intake hose of the
vacuum pump to the nipple of
the test flange.
- Check that the spark plug is
secure.
• Close venting screw (1) on the
pump piston.
• Actuate lever (2) until a vacuum
of 0.5 bar is indicated on the
pressure gauge.
Note: The rotary shaft seals are in
perfect working order if the indicated
negative pressure is maintained or if
the pressure does not rise above
0.4 bar within 20 seconds. If the
pressure continues to increase
(elimination of negative pressure in
crankcase), however, the rotary shaft
seals must be replaced even if the
vacuum test did not reveal any leaks.
- Reopen venting screw and
remove hose after testing.
- Remove test flange and install
carburetor as described in
chapter 10.2.2.
- Unscrew muffler screws.
- Draw out sealing plate.
- Tighten muffler screws with a
torque of 10.0 Nm.
- Fit shroud, see chapter 5.5.
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