GENERAL INFORMATION
When replacing a thermocouple ensure replacement is same type as one removed by
ensuring part number/wire colors match. If stagger does not match use stagger
adapter P/N 42523. In a new installation, make sure the location on a single probe
(thermocouple) Exhaust Gas Temperature system is in the exhaust pipe of the cylin-
der that is leanest during full throttle. Particularly in carbureted engines, the leanest
cylinder can change when throttle, altitude, carburetor heat, and/or ambient air temper-
ature changes. The leanest cylinder is the one that reaches peak first when leaning
from full rich, which is sometimes the cylinder with the highest EGT. Additional informa-
tion on mixture management can be found in
Alcor's
®publication EGT Combustion
Analysis in a Nutshell and Lycoming Service Bulletin 1094D, and Continental Service
Bulletin M89-18. The probe should be located a minimum of 2 inches from the cylinder
exhaust port flange (5 inches for highly supercharged engines) in an area free from
weld beads or pipe irregularities. If the pipe has a longitudinal weld bead, orient the
clamp so that the bead does not interfere with flush fit of shoulder of flange at base of
probe tip (gas seal). Determine the location that will allow probe and wire to be free
from interference with spark plugs, baffling, cowling, exhaust and other components.
For screw-in type
Alcor
®probes use weld boss, P/N 28113 located the same distance
as clamp style probes or 3-5 inches from the turbocharger inlet in Turbine Inlet
Temperature sensing applications. All work to be done in accordance with FAA,
Advisory Circular 43.13-1B or later revision.
INSTALLATION, CLAMP TYPE
1. For new installations, carefully drill a hole at selected location using a #31 (0.120
inch/3.05mm) or #32 (0.116 inch/2.95mm) drill. If available, carefully ream hole using
#30 (0.1285 inch/3.26mm) drill. The correct hole size and alignment assures a press
fit of probe element shoulder to prevent exhaust gas leakage.
2. Open clamp and place around exaust pipe ensuring correct orientation of clamp tight-
ening screw. Place probe tip into hole and tighten clamp to remove looseness.
3. While probe element is perpendicular to exhaust carefully push and rotate probe to
fully seat element shoulder to exhaust pipe. If necessary use a small wooden dowel
and light hammer or other suitable tool to lightly tap clamp at junction of probe body
to seat probe shoulder.
4. Torque clamp to 30-35 inch pounds and cut off excess clamp and deburr. To ensure
clamp does not loosen during operation it may be safety wired from the end of slot-
ted clamp tab to body of probe or slot in screw may be safety wired to screw hous-
ing.
5. Slide fiberglass insulation sleeve over lead. Connect instrument lead to probe lead
with screws and nuts ensuring correct stagger/color combinations. Slide sleeve over
lead connection and secure with nylon ties.
6. Allow enough slack in probe lead to provide a finger-sized loop (see Figure 1) to
minimize strain on wire and secure remainder of lead to engine/airframe away from
exhaust pipe.
INSTALLATION, SCREW-IN TYPE
1. For new installations, carefully drill a hole at selected location using a #30 drill. Insert
probe into weld boss and hand tighten. Insert probe tip into drilled hole and tack
weld boss. Remove probe and weld boss to exhaust pipe.
2. Drill a .125 inch hole through the exhaust pipe at the center of the boss taking care
not to damage internal threads in boss.
3. Insert element into exhaust no deeper than .75 inch (see Figure 2).OPTIONAL- lubri-
cate probe threads with high temperature lubricant (2000°F)
4. Tighten probe nut finger tight, then with appropriate sized wrench tighten an addi-
tional 3/4 turn or till snugly locked in place.
Follow steps 5 and 6 above to complete installation.
FREQUENTLY ASKED
QUESTIONS
On a new single probe installa-
tion, which cylinder do I install
the thermocouple on?
This would be the cylinder where
the temperature peaks first while
leaning. Not all engines, even of the
same make and model, will peak the
same due to differences in internal
airflow characteristics, carburetion,
injection, etc. A worst case scenario
would be installing the probe on the
richest running cylinder (peaks last)
where lean misfire would be
reached before peak while leaning.
I installed a new probe and the
meter is still dead or went dead
again after being in operation for
awhile?
First make sure that the correct type
of probe was installed by verifying
color code matches lead and meter
(Type K, Red/Yellow, or Type E,
Red/Brown). If that checks all right
then disconnect the lead from the
meter and measure the loop resist-
ance of the lead and probe and
compare it with the value marked on
– 2 – – 3 –
NOTE: This is typically the recommended depth of
insertion for all
Alcor
®thermocouples.
Alcor
®P/N Type Color Resistance @ 70°F Millivolts at 1550-1650°F Weight Size
All Clamp K Red/Yellow .6 -1.0 ohm 34.12 - 36.36 mV .12 lbs 3.25 max dia.
All Screw-in K Red/Yellow .6 -1.0 ohm 34.12 - 36.36 mV .12 lbs call
All Clamp E Red/Brown .7 -1.0 ohm 63.04 - 67.33 mV .12 lbs 3.25 max dia.
All Screw-in E Red/Brown .8 -1.1 ohms 63.04 - 67.33 mV .12 lbs call
the meter label. If the value is approximately the same then the problem is most like-
ly the calibration potentiometer or the movement in the meter. The old probe removed
is probably good! Call
Alcor
for repair of meter.
Is there any way I can test a thermocouple without expensive equipment?
Yes, by using an
ALCAL
®
2000
EGT/CHT System Tester. If not available then meas-
ure the loop resistance (see resistance table) of the probe with a digital multi-meter, if
available. While viewing display, move probe wire to detect internal wire breaks. If the
reading is steady then the probe is probably good. When heated to just turning red,
the temperature is about 1550-1650°F.
RESISTANCE AND WEIGHT ARE APPROXIMATE
Figure 2. Welded Boss Type
