Checking The Compression - Rotax 914 Series Maintenance Manual

2.6)

Checking the compression

See Fig. 11.
▲ WARNING: Ignition switch for both ignition circuit in "OFF" position.
Testing is carried out using the differential pressure test procedure.
■ CAUTION:
PROCEDURE:
Bring engine to operating temperature. Move crankshaft to ignition TDC
position.Unscrew the bottom spark plug in each case to prevent dirt particles
penetrating the engine. Screw adaptor (1) into the sprak plug thread and
connect up the two pressure gauges with the orifice jet (2) between them. Now
put constant pressure (4) on the line (3) and take readings at pressure gauge
(5). The maximum permissible pressure drop is 25 %, e.g. from 6 to 4.5 bar
(87 psi to 65 psi).
If the value is below 4.5 bar (65 psi), inspection, repair or overhaul must be
carried out in accordance with the BRP-Rotax instructions for continued
airworthiness.
- Detailed inspection of affected engine components.
◆ NOTE:
* or equivalent e.g. orifice diameter 0.040 in., long 0.0250 in., 60 degree
approach angle according to AC43.13, latest edition.
Effectivity 914 Series
Edition 1 / Rev. 1
BRP-Rotax
MAINTENANCE MANUAL
For this test, you will need the following equipment:
Compressed air supply of approx. 6 bar (87 psi), and a testing
device consisting of two pressure gauges, an orifice jet (2)*
of 1 mm (0.04 in) inner diameter and 3 mm (0.12 in) length and
an adaptor to connect line to tapped spark plug thread.
In the course of fault-tracing a compression check can also be
performed:
bar
1
1
Zyl. Kopf /
cyl. head
07621
5
5
4
bar
Ø 1mm (0,039 in.)
L = 3 mm (0,12 in.)
3
2
Fig. 11
12-00-00
page 10
Sept. 01/07