Vacuum Test - Stihl MS 460 Service Manual

– If the pressure drops, the leak
must be found and the faulty part
replaced.
To find the leak, coat the suspect
area with oil and pressurize the
crankcase again. Bubbles will
appear if a leak exists.
– After finishing the test, open the
vent screw and disconnect the
hose of tester 1106 850 2905.
– Continue with vacuum test,
b 6.2.3
28
6.2.3

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.
An additional test can be carried out
with the vacuum pump to detect this
kind of fault. Carry out the same
preparations as for the pressure
test, b 6.2.2
: Connect suction hose (arrow) of
vacuum pump 0000 850 3501 to
nipple (arrow) of the test flange.
3
1
: Close the vent screw (1) on the
pump.
: Operate lever (2) until pressure
gauge (3) 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
crankcase), the oil seals must be
replaced.
– After finishing the test, open the
vent screw and disconnect the
hose.
– Remove the test flange.
– Install the carburetor, b 12.2.1
– Loosen the muffler screws and
remove the sealing plate.
– Take out the screws one at a time
and refit with Loctite, b 16.
– Tighten down the screws firmly –
b 3.5
– Mount the muffler top casing.
– Unscrew the plug from the
cylinder.
– Install the decompression valve,
b 6.8
2
MS 460, MS 460 C