Jabiru Aircraft
Pty Ltd
Installation Manual
Jabiru 3300 Aircraft Engine
REVISION
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Dated : 1
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Dec 2016
Page: 21 of 56
4.8.5
Cylinder Head Temperature Gauge
The Cylinder Head Temperature Gauge uses a thermocouple which is installed to the screw between the
spark plugs or under exhaust spark plug of each cylinder head. CHT probes fitted under the spark plug are
susceptible to reading errors if not positioned concentrically. It is highly recommended that that CHT probes
by fitted instead on the bridge between the two plugs (as shown in Figure 24).
The head temperatures of air cooled engines are typically quite variable
– differences of 50°C (90°F)
between the hottest and coolest head are not uncommon. Refer to Section 12 for additional information on
cooling.
For a new installation an audit must be done to establish which is the hottest cylinder. The CHT
thermocouple probe is then fitted under the exhaust spark plug on that cylinder. Cylinder number 4 often
runs hottest in normal tractor installations, however for new installations this MUST be checked and
confirmed. Jabiru Part No. PI10732N is the recommended gauge.
Care must be taken when installing the spark plug terminal
– the terminal must be aligned with the spark
plug. If the terminal is not aligned the spark plug seal will be poor and hot combustion gasses can leak out.
These very hot gases will cause the thermocouple to mis-read and
show high CHT’s. Figure 23 shows
properly and improperly fitted CHT terminals.
If thermocouple cable is too long it must be looped as many times as necessary and strapped behind the
instrument panel or to the engine mount.
DO NOT CUT TO LENGTH
The Thermocouple sensor works by reading small voltages generated by the sensor wires, and cutting the
wire upsets the instrument’s calibration.
Ensure that wire is not chaffing on the fibreglass air duct or cooing fins.
No power connection is required for analogue gauges
– the instrument reads directly off the voltage created
by the thermocouple wire.
Follow manufactures instructions when installing gauges, they will have specific installation requirements.
Temperature of the cold junction for best results should be around 50ºC. Ensure cold junction is mounted
as far from the thermo couple probe as possible.
Figure 22. CHT Sender (Thermocouple) Installation
CHT Thermocouple
Cold Junction Spark Plug Terminal
Cold Junction
Plug terminal under spark plug
