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http://www.ultralightnews.ca/ Page 15 of 39
The Ultralight Store - your one stop ultralight store.
CHT temperatures in excess of 280°C or 536°F are a result of :
Lack of oil in fuel or NO oil in the fuel.
Poor piston cylinder lubrication, due to poor quality of oil.
The use of a fan belt other than that supplied by Hirth, a loose, or damaged fan belt.
Ablocked fan intake duct, or blocked cylinder head fins. (Insect nesting, mice etc.).
Insufficient cooling due to air intake design.
Pre-ignition or detonation, caused by old fuel, improper octane, ignition timing.
3.2Exhaust gas temperature
Agauge that we recommend on all Hirth two stroke engines is the Westach Exhaust Gas Temperature gauge
(EGT) as in figure 3.2.1. This gauge is a reliable measurement tool that measures the exhaust gases as they
exit the engine. A rich fuel/air mixture which can be caused by improper jetting, clogged air filter, improper
prop setting, will generally show up as a cooler temperature. A too lean mixture can be caused by an air leak
or fuel blockage, can result in overheating and engine seizure.
Figure 3.2.1 Westach Dual EGT 029.30
The proper location of the EGT probe on the exhaust manifold is extremely important. Mounting the probe
too close or too far from the piston will result in an incorrect reading.
If the engine is installed with one carburettor, the probe needs to be located in the centre of one of the
exhaust manifold ports 85mm from the exhaust outlet of the engine cylinder exhaust port. If the engine is
installed with two carburettors, each probe needs to be located in the centre of each of the exhaust manifold
port, 85mm from the exhaust outlet of the engine cylinder exhaust port. Install the probe before reinstalling
the manifold and make sure the probe will not touch the other side of the manifold wall.
The 50mm round EGT the gauge will mount from the front of the panel and will require a 52.388mm round
hole, a U bracket holds it in place from the rear.
The EGT gauges require probes which come with 100mm of lead. To install the probe, drill a 4.763mm hole
in the centre of the exhaust pipe at the recommended distance above. Install the probe into the hole, and
tighten up the clamp. As an option, manifolds are provided to suit the "bayonet probe" type. The terminal
cable can be lengthened to a maximum of 4.5 metres without affecting the accuracy of the instrument.
Route all wires away from the manifold and other heat sources. Support the wires every 300mm intervals,
using tie wire or similar. When going through firewalls etc, use rubber grommets to prevent damaging the
wiring. Do not route these wires with any wires from an AC source, such as a lighting coil, spark wires, tech
wires, etc. The EGT operates on .004 millivolts. Running near an AC source will result in incorrect
readings.
It is important that you verify the EGT readings by careful examination of the spark plugs. A reading on an
EGT of 1100 to 1200 degrees F should give a nice tan coloured spark plug. Lower readings should give
darker colours while higher readings grey/white colours.
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