Jabiru Aircraft
Pty Ltd
Instruction & Maintenance Manual
Jabiru 2200 Aircraft Engine
Hydraulic Valve Lifter Models
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REVISION
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Dated : June 2010
Issued By: DPS
Page: 29 of 116
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The carburetor automatically adjusts the mixture to account for altitude.
IMPORTANT
Check carburetor joints for degradation.
Check carburetor linkage for full & free movement, correct positioning of stops and
security.
6.4
Compression Check
6.4.1
Compression Gauge:
Measure compression using a compression tracer. Readings are taken with fully open
throttle valve at engine oil temperature between 30
°
& 70
°
C (90
°
to 160
°
F).
If readings are below 6 bar (90 psi) a check of the pistons, cylinders, valves & cylinder
heads must be undertaken.
6.4.2
Pressure Differential Test:
Check using a pressure loss or leakage tester eg SUN or BOSCH tester; max.
allowable pressure loss is 25%.
As an alternative to a compression test, a pressure differential test (Leak down) can be
carried out. This is a much better test of the condition of rings, bore, head sealing and
valve. This is the normal test used in aviation and requires specific equipment.
The test is carried out with the engine in warm to hot condition. Input pressure is best
set at 80 PSI; a second gauge reads the differential. This is done with piston on TDC
on the firing stroke. Note that the propeller needs to be restrained. A differential of
lower than 80/60 (or generally, a 25% loss) indicates a problem.
Problems can be better identified using the leak down:
i)
Blow by through the crankcase vent indicates worn rings or bore
ii)
Leaking from carby indicates a poor intake valve seal
iii)
Leaking from exhaust indicates a poor exhaust valve seal
iv)
Head leak indicates poor head to cylinder seal
With the problem narrowed down, correction work can more easily be carried out.
A Pressure Differential Tester can be made by placing an orifice of 1 mm ID and 3mm
length between two pressure gauges. This will give the same result as with the above
instrument. Max. pressure drop is 25%.
CAUTION: Poor compression can be an indication of a serious problem.
For
example, continued operation with poor compression due to a poorly-sealing valve can
lead to eventual
valve failure
and
heavy damage to the piston, con-rod, barrel and
head. If low compression is found which cannot be solved by reference to the
Troubleshooting section below, please contact Jabiru Aircraft or our local
authorized representative.
