TM 1-1500-204-23-4 · Use   heater   probes   designed   for use on the engine thermocouples to be tested. Temperature gradients  are  very  critical  in  the design   of   heater   probes.      Each type  of  aircraft  thermocouple  has its  own  specially  designed  probe. Never   attempt   to   modify   heater probes    to    test    other    types    of thermocouples. · Do not leave heater probes assemblies  in  the  tailpipe  during engine runup. · Never  allow  the  heater  probes  to go over 1,652F (900C). Exceeding these temperatures will result in damage to the jetcal analyzer and heater probe assemblies. (5) Maintenance.  Apply a few drops of oil to hinges,  then  wipe  off  excess  oil  with  clean  cloth.    With wheels   removed,   apply   a   light   coating   of   grease   to wheel mount axles. 4-3. Instruments and Instrument System Maintenance.      General   maintenance   procedures   for instruments and instrument systems are covered in the following    paragraphs.        General    precautions    are    as follows: · Instruments  are  delicate  devices and  will  always  be  handled  very carefully. · Always   replace   instruments   with another of like kind and type, or a suitable    substitute    as    listed    in applicable repair parts appendixes and special tool lists. · Configuration  of  aircraft  (location and  positioning  of  instruments  or components)   will   not   be   altered unless authorized by AVSCOM. · Never exceed pressures or values specified   in   publications   dealing with     test     procedures     for     that particular instrument. · Thread compound will be used on all  threaded  coupling  connectors (except electrical) of the instrument system. Thread compound shall be applied so that entrance  into  gauge  is  prohibited (i.e.,  apply  a  light  coating  to  two threads  of  male  end,  starting  at second thread). Pliers and adjustable   wrenches   will   not   be used on coupling connectors. a.  Inspection of Instrument Systems.  Instrument systems  will  be  inspected  and  functionally  checked  in the aircraft.  However, indicators or transmitters may be removed from the aircraft and bench checked whenever facilities permit. b.    Inspection  Requirements.    Use  the  following paragraphs to inspect instruments. (1)  Range  markings.    Instruments  must  be range-marked   in   accordance   with   applicable   operator manual and TM 55-1500-345-23. (2)   Mounting.      Shock-mounted   instrument panels   will   be   free   to   move   in   all   directions   with   a minimum  clearance  of  1/4  inch  between  panel  and  its supporting   structures.      When   panel   does   not   have specified   clearance,   inspect   rubber   shock   mounts   for looseness,  cracks,  or  deterioration.    Loose  mountings will be tightened, and cracked or deteriorated mountings will be replaced. (3)   Connecting   lines.      Wiring   or   flexible tubing  behind  instrument  panel  will  be  sufficiently  long to permit easy connection to indicators (a minimum of 4 inches  in  front  of  panel).    All  electrical  wiring  will  be anchored  to  prevent  swinging  or  sagging,  but  must  not interfere with free movement of shock-mounted instrument panel. NOTE Examine all instrument connection threadings and all line connection  threadings  to  be  sure they are the same thread.  Do not force under any circumstances. (4)  Operation  of  instruments.    Instruments must   operate   satisfactorily   as   required   by   applicable operator   manuals.      Instruments   that   do   not   operate satisfactorily will be replaced. (5)      Physical   defects.      Instruments   with physical defects or damage must be replaced. (6)     Corrosion.          Replace     instrument     if corrosion damage is present. (7) Color coding.  The Army uses two types of   identification   systems   to   color   code   the   plumbing lines    and    electrical    conduits    of    aircraft.        The    two systems  used  are  the  printed-symbolized  tape  system, the preferred 4-9