VALVE & LINES GP-AUXILIARY 4645060 - Caterpillar

1 Place pyrometer (1) in a location free from excessive vibration. Turn the selector switch to (0) position when the unit is not in use; this dampens needle movement and the unit is less susceptible to damage from vibration or shock. 2 Install thermocouple (2)*. One of the following adapter bushings may be required; 4M5317 - 1/8" × 1/4" NPT; 3B7721 - 1/8" × 3/8" NPT; 8B1931 - 1/8" × 1/2" NPT. The tip of each thermocouple should reach the center of the exhaust pipe or chamber; all tips should have the same spacing from exhaust ports. Refer to the chart on page 15 for probe installation location. *IMPORTANT: The fitting on thermocouple (2) is only initially adjustable. When sealing nut (3) is tightened, the ferrule is imbedded into the metal and cannot be repositioned. 3 With fitting (3) positioned as shown, thermocouple (2) will adapt to most exhaust systems. 4 When tube length-to-thread distance must be shortened, add a 20639 Adapter (4) as shown, or position fitting (3) to the correct length required. If additional 20639 Adapters (4) are needed, they must be drilled out with a .266" Ø (6.8 Ø) drill so they will slide over the .250" Ø (6.4 Ø) thermocouple tube. In situations where thermocouples are used temporarily in a number of engines where probe depth requirements vary, it may be advisable to have several thermocouples (2), each with a fitting (3) for various short length and long length positions. Additional fittings (3) can be made using a 1P3861 Connector, 3D8093 Nut and a 3D8094 Sleeve. 5 Fasten the thermocouple leads to the pyrometer; fasten white wire (+) to white terminal (+) and red wire (-) to red terminal (-). Approximately every six months or after rough handling of the instrument, check the reference junction temperature. See ADJUSTMENT OF REFERENCE JUNCTION TEMPERATURE. 6 Turn the selector switch to bring into the circuit whichever thermocouple is to be measured and then observe the pointer. Temperatures may be quite variable from engine to engine (same model) and from cylinder to cylinder. Factors that affect engine exhaust temperature are: 1. Air cleaner restriction2. Exhaust restriction3. Ambient temperature4. Internal friction of the engine5. Fuel rate, fuel system condition or settings6. Altitude7. Valve portings8. Thermocouple condition9. Thermocouple locationConsequently, exhaust temperature, by itself, is not a reliable method of determining engine condition. Pyrometers can best be used in detecting a temperature change from one inspection to another, or indicating a gradual increase or decrease in temperature over a period of time. If specific information is needed for temperatures expected for a particular engine, make reference to the Technical Information File. 7 When the pyrometer fails to respond to sudden changes in exhaust temperature, remove the accumulated carbon from the stem of thermocouple (2). Thermocouples can be checked by using an accurate ohmmeter across the leads; 120" (3048) lead 8L4439 Thermocouples should read 2.2 ohms and 480" (12192) lead 1N7494 Thermocouples should read 8.7 ohms.
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