Rotax 912-UL Repair Manual page 26

6.6) Cylinder head'
6.6.1) Check of compression
Leakage test is normally carried out prior to disassembly, with engine still complete.
The compression testreveals a lot about the condition of the engine; this test tells also
if the valves are in correct order or worn out, and in addition, it will indicate when
a complete overhaul is due.
Leakage test: .
It needs a compression tracer to check compression. The pressure should be between
9 and 12 bar (130 and 174 psi).
PROCEDURE: Bring engine to operating temperature. Remove top spark plug and
press compression tracer against plug tap hole and set engine into rotation by
activating starter until maximum pressure is reached. Successively take readings on
all four cylinders and compare results. Individual readings of the cylinders most not
differ by more than2 bar (29 psi).
Pressure difference method :
For this method you need the following: Compressed air supply of 5 to 7 bar (72to
100 psi), two pressure gauges, an orifice of I mm (0,04 in.) 6 and 3 mm (0,12 in.)
Iength and an adaptor to connect line to plug tap-hole.
PROCEDURE: Bring engine to operating temperature. Lock crankshaft in T.D.C.
Removerespective sparkplugandfitadaptorOinstead, andconnectlinewith the two
pressure gauges and intermediate orifice O. Now put constant pressure on the line O
and take readings on pressure gauges O and 6. The maximum allowable pressure
drop is 33 Vo (e.g. from 6 bar | 87 psi to 4bar /58 psrF
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