Installation manual

GEM INSTALLATION MANUAL DOCUMENT No. 070906 REV. 1.4
INSIGHT
INSTRUMENT CORP. 11 BOX 122, FORT ERIE, ONTARIO, L2A 5M6
If the probe must be positioned in a slip joint the inner tube must have a clearance hole of at least 1/4”
diameter to prevent it from shearing the probe. Be certain to locate all holes to allow straight-in insertion of the
probe without bending or stressing the probe tip.
Before drilling, ensure that nothing interferes with the probe, clamp, clamp screw or wire. Center punch and
pilot drill each hole in the exhaust stack with a No. 28 or 9/64” drill bit. Use caution while drilling perpendicular
to the stack to prevent an elongated hole. NOTE: Tighten the clamp screw with hand-torqued nut driver only.
A right angle drill extension may be necessary in some locations. The probe will slip into a carefully drilled hole
and make a tight seal.
Installing The Cylinder Head Temperature Probes
There are three types of Cylinder Head Temperature (CHT) probes:
· Spring Probe (Part Number 2852)
· Spark Plug Gasket Probe (Part Number 2853)
· Adapter Probes (Part Numbers 2855 Bayonet Adapter, and 2856 Threaded Adapter)
The Spring Probe (Part Number 2852) is equivalent to the “old style” Bayonet Probe and screws into threaded
thermo-wells in the cylinder head next to the lower spark plug (on top in some engines).
The Spark Plug Gasket Probe (Part Number 2853) replaces the copper 18 mm diameter spark plug gasket.
The Bayonet Adapter Probe (Part Number 2855) screws directly into the temperature well and replaces the
standard bayonet adapter to allow simultaneous utilization of the factory-installed Bayonet Probe.
The Threaded Adapter Probe (Part Number 2856) is similar to the 2855 except it is threaded on the inside to
allow simultaneous utilization of the factory-installed Threaded CHT Probe.
CHT Probe Characteristics
The Spring Probe (2852) has a probe bushing with a screwdriver slot to facilitate tightening into place. A drop
of anti-seizing lubricant on the threads before installation will ease installation, and subsequent removal. When
installing Spring Probes be sure you have correctly identified the standard thermo-well. Some aircraft have fuel
primer ports with the same thread size.
Many factory-installed CHT displays utilize a single threaded or bayonet-style resistive type probe that
occupies one of the thermo-wells. This probe is not electrically compatible with the thermocouple probes
required for the Graphic Engine Monitor.
A Spark Plug Gasket Probe (2853) may be used on this cylinder for the GEM series Display, so as to allow the
factory-installed display to remain functional.
The Spark Plug Gasket Probe replaces the standard copper spark plug gasket on one spark plug in the select-
ed cylinder. The spark plug chosen should be the one that provides the best correlation with the other
temperature probes. On common downdraft-cooled engines the selected cylinder will be the upper plug. Allow
enough wire length to move the probe to the other plug if necessary.