© STIHL Inc., Virginia Beach, VA 2013 US/STR
confidential
26. Vacuum and Pressure Test of Crankcase
Use the tester to pull a 0.5 bar vacuum; it should hold steady
or not leak back to 0.3 bar within 20 seconds
Rotate the crankshaft back and forth while the crankcase is
under vacuum to verify that the seals are holding properly
Pump 0.5 bar of pressure into the engine and it should hold
steady for at least 20 seconds
© STIHL Inc., Virginia Beach, VA 2013 US/STR
confidential
Pressure Test Results
If the unit fails the pressure test check obvious things first, such
as the rubber sealing plate on the exhaust and the spark plug,
by spraying with soapy water and looking for bubbles
If they are sealing properly then the engine may need to be
taken apart far enough to be able to check the crankshaft seals
and the seal between the cylinder and the crankcase
If an engine leaks under vacuum but holds under pressure it is
most likely a crankshaft seal
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