Checking The Compression - Rotax 912 iSc Maintenance Manual

4) Checking the compression

See
General note
To measure the compression pressure the following special tools and
Special tools
equipment are necessary.
n.a.
n.a.
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Testing is carried out using the differential pressure test procedure.
Instruction
Step
1
2
3
4
5
6
The maximum permissible pressure drop is 25 %, e.g. from 6 to 4.5 bar
Value
(600 kPa to 450 kPa) (D).
If the pressure loss is less than 25% then the valve seats and piston rings
are working properly. The spark plug has to be installed according to
chapt. 12-20-00 section: 14.2).
If the value is over 25% inspection, repair or overhaul must be carried out
in accordance with the BRP-Powertrain instructions for continued airwor-
thiness.
- Detailed inspection of affected engine components.
Effectivity: 912 i Series
Edition 1/Rev. 0
BRP-Powertrain
MAINTENANCE MANUAL
Fig. 2.
Risk of electric shock!
WARNING WARNUNG
Ignition "OFF" and system grounded!
Part number
Compressed air approx. 6 bar (600 kPa).
2 pressure gauges.
Orifice jet*, of 1mm (0.04 in) inner diameter and 3 mm (0.12 in)
length.
* or equivalent e.g. orifice diameter 0.040 in., long 0.0250 in.,
60° degree approach angle according to AC43.13, latest issue.
Adapter to spark plug thread.
Connect line.
Operate the engine until the temperatures have stabilized for a period of 5 min
(engine oil temperature between 50 to 70 °C (122 - 160 °F).
Starting with cylinder head 1 move piston to TDC position.
Remove the upper spark plugs. Prevent dirt or other foreigner particles from
penetrating the engine (A).
Screw adaptor (1) into the spark plug thread and connect up the two pressure
gauges (2) with the orifice jet (3) between them (B).
Now put constant pressure, between 5.5-6 bar (550-600 kPa) on the line and
take readings at pressure gauge (C).
Repeat this proceeding at all 4 cylinder heads.
Description
Procedure
12-20-00
page 9
January 01/2012