Leakage Test; Pressure Test - Stihl 4141 Series Manual

5.3

Leakage Test

Defective oil seals and gaskets or
cracks in castings are the usual
causes of leaks. Such faults allow
supplementary air to enter the
engine and thus upset the fuel-air
mixture.
This makes adjustment of the
prescribed engine idle speed
difficult, if not impossible.
Moreover, the transition from idle
speed to part or full throttle is not
smooth.
The crankcase can be checked
thoroughly for leaks with the carbu-
retor and crankcase tester and the
vacuum pump.
– Remove shroud - see 5.1.
– Make sure the spark plug is
properly tightened down.
– Remove the air filter and
carburetor - see 9.1 and 9.3.
– Set the piston to top dead center
(T.D.C.). This can be checked
through the intake port.
1
2
Mount test flange (1)
4141 850 4200 to spacer flange
with M5 x 40 screws (2).
12
2
Release muffler mounting screws
(2) and back them off half-way.
Slide the sealing plate (1)
0000 855 8106 between the
gasket and cylinder and retighten
the mounting screws moderately.
Note:
The sealing plate must completely
fill the space between the two
screws.
5.3.1

Pressure Test

1
1
2
Connect pressure hose (2) of
tester 1106 850 2905 to nipple on
test flange (1).
Close the vent screw (1) on the
rubber bulb.
– Use rubber bulb to pump air into
the crankcase until the gauge
indicates a pressure of 0.5 bar
(7.25 psi). If this pressure
remains constant for at least
20 seconds, the crankcase is
airtight.
– If the pressure drops, the leak
must be located and the faulty
part replaced. Repeat the
pressure test in such a case.
Note:
To find the leak, coat the suspect
area with oil and pressurize the
crankcase again. Bubbles will
appear if a leak exists.
– Open the vent screw and
disconnect the hose.
– The pressure test must always be
followed by a vacuum test.
Series 4141 Powerhead
1