Engine Maintenance Manual
Jabiru Aircraft
Pty Ltd
JEM0002-5
Jabiru 2200 & 3300 Aircraft Engines
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ISSUE
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Dated : 2nd June 2015
Issued By: AS
Page: 70 of 103
L:\files\Manuals_For_Products\Engine_Manuals\Engine Maintenance Manual 22 & 33\JEM0002-5.docx
Maximum allowable pressure loss is 25% - therefore a differential of lower than 80/60 indicates
a problem.
CAUTION
The propeller must be restrained as the air pressure applied will tend to rotate the crank.
While the pressure is being applied, lightly tap the tip of the rocker arm where it touches the
valve using a soft hammer. The aim is to bounce the valve off its seat by around 1
– 2mm.
The air pressure applied by the tester will press the valve back into place quickly and any
debris which had gathered around the valve sealing face will be jolted free and blown out of the
combustion chamber. This will often improve the valve seal enough to raise the compression
of the cylinder by several psi.
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.
Note: for commercial use, proper calibration of this tool is necessary.
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.
After testing, note the results in the maintenance worksheet and re-assemble the engine.
9.18.3 Identifying Compression Leaks
Problems can be better identified using the leak down:
i)
Remove the dipstick and listen at the opening. Air leaking through here indicates worn
rings or bore
ii)
Disconnect the SCAT hose from the carburettor intake and listen at the opening. Air
leaking from carburettor indicates a poor intake valve seal.
iii)
Listen at the exhaust outlets
– air leaking from exhaust indicates a poor exhaust valve
seal.
iv)
Apply a small amount of soapy water to the base of the head, where it mounts to the
cylinder. A head seal leak will be indicated by blowing bubbles in the soap mixture.
Alternative to listening, a rubber glove or similar can be stretched over the opening being
checked (carburettor inlet, exhaust outlet, crankcase vent); if the glove inflates this indicates
the location and rate of the leak.
With the problem narrowed down, correction work can more easily be carried out.
9.19
Fuel Flow Rate Test
Required Tools:
Screwdrivers
Container with accurate volume marks
Clock or stopwatch
Parts and Material:
N/A
Type of Maintenance:
Line Maintenance
Level of Certification:
L1, L2 or LAME (Owner, A&P or LSA Repairman / Maintenance)
Return to Service:
L1, L2 or LAME (Owner, A&P or LSA Repairman / Maintenance)
Disconnect the fuel line from the mechanical fuel pump in the engine compartment.
Have a second person stand by to catch any fuel that flows out of the line in a container with
accurate volume marks. Ensure the free end of the fuel hose is held level with the carburettor
fuel inlet.
Turn electric fuel pump on and pump fuel through the lines into container. Ensure there is
about 1 litre per minute flow rate (50-60 L/hr).
Re-connect the fuel line.