Vacuum Test - Stihl 064 Service Manual

STIHL 064, 066
Test setup with carburetor and
crankcase tester 1106 850 2905
- Use rubber bulb to pump air into
the crankcase.
The gauge must indicate a press-
ure of 0.5 bar (7.25 psi). If this
pressure remains constant, the
crankcase is airtight. However, if
the indicated pressure drops, the
leak must be located and the
faulty part replaced. Coat the sus-
pect area with oil and pressurize
the crankcase again. If bubbles
appear in the oiled area, replace
the faulty part.
- After finishing the test, open the
vent screw and disconnect the
hose.
Reassemble the machine in the
reverse sequence.
Note: Coat the mounting screws
of both muffler casings with Loctite
(see 12.2), refit them and tighten
to the specified torque - see 4.1.
4.6.3

Vacuum Test

Test setup with vacuum pump
0000 850 3500
Oil seals tend to fail when sub-
jected to a vacuum , i.e. the seal-
ing lip lifts away from the crank-
shaft during the piston's induction
stroke because there is no internal
counterpressure.
An additional test can be carried
out with the vacuum pump to de-
tect this kind of fault. The prepara-
tions for this test are the same as
for the pressure test - see 4.6.2.
- Connect the vacuum pump's
suction hose to test flange nipple.
- Pull out the pump piston several
times until the gauge indicates a
vacuum of 0.5 bar (7.25 psi).
Note: When you release the pump piston,
the non-return valve automatically seals the
suction hose.
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.
However, if the pressure continues to rise
(reduced vacuum in crankcase), the oil
seals must be replaced, even if no leaks
were detected in the pressure test.
- After finishing the test, discon-
nect the hose.
Reassemble the machine in the
reverse sequence.
Note: Coat the mounting screws
of both muffler casings with Loctite
(see 12.2), refit them and tighten
to the specified torque - see 4.1.
43