Vacuum Test - Stihl MS 270 User 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.
– Continue with vacuum test
– see 6.2.3
MS 270, MS 280
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 vacuum pump to detect this
kind of fault. Carry out the same
preparations as for the pressure test
– see 6.2.1.
Connect suction hose (arrow) of
vacuum pump 0000 850 3501 to
nipple of test flange.
3
1
Close the vent screw (1) on the
pump.
Operate lever (2) until the
pressure gauge (3) indicates a
vacuum of 0.4 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
– see 12.2.1.
– Remove the screws from the
cylinder. Remove the sealing
plate.
– Mount the muffler –
– On engines with decompression
valve, unscrew the plug from the
cylinder, see
decompression valve –
2
see 6.1.
6.2.1, and install the
see 6.8.
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