TM 55-2840-241-23 (7) Hold the fitting in its position and tighten the  nut  against  the  boss. b. Use  this  procedure  to  install  universal  fittings without backup rings. (See figure 5-1.) (1) Run the nut on the fitting end back until the washer face is aligned with the upper inner comer of the  seal  groove. (2) Lubricate seals used on oil, anti-icing, and bleed  air  tube  fittings  with  lubricating  oil  (item  7, table 2-2). Lubricate seals used on fuel tube fittings with lubricating oil (item 8, table 2-2). DO NOT lubri- cate seals used on fuel system control air tube fittings. Place the seal in the seal groove. (3) Screw the fitting into the boss until the seal barely touches the boss. (4) Turn the fitting and nut together until the nut touches the boss. (5) Put a wrench on the nut to prevent its turn- ing, and position the fitting by turning it in up to 270° or unscrewing it up to 90°. (6) Hold the fitting in its proper position and tighten the nut against the boss. 5-4.1.   Airframe/Engine   Interface   Connection. Refer  to  table  5-1  for  the  recommended  torque  values of  airframe  fittings  installed  into  the  engine  at  the airframe and engine interface. Table 5-1. Recommended Torque for Airframe/ Engine Interface Connections. Thread   Size Torque lb  in. Nm ().375-24 25-40 2.8-4.5 0.4375-20 40-65 4.5-7.3 0.500-20 60-80 6.8-9.0 0.750-16 150-200 17-23 0.875-14 200-350 23-40 1.0625-12 300-500 34-56 5-5. Rigid Tube Installation. Failure of engine pneumatic or fuel tubes due  to  faulty  maintenance  practice  could cause  flameout,  power  loss,  or  overspeed. The  practice  of  tightening  lock  nuts  with tube  assemblies  installed  can  cause  tube damage and failure of the tube assembly. a. Tube  assemblies  must  fit  and  be  aligned  with  the mating  flare  tube  fittings  to  the  degree  that  at  both ends of the assembly the flares shall uniformly seat in a free state on the cones of the mating fittings. The fit shall  be  without  distortion  or  stretching  of  the  tube assembly and to the degree that the nuts can be fully engaged  up  to  the  final  one-half  turn  with  light  finger pressure. b. In the event a tube does not align with the mating fittings,  reposition  the  mating  fittings  to  the  degree that proper alignment may be attained. Final tighten- ing of these fittings must be accomplished before the tube assembly is connected. c. If  proper  alignment  cannot  be  attained  by  reposi- tioning  mating  flare  tube  fittings,  bend  the  tube  suffi- ciently to provide alignment in the free state as spec- ified. Accomplish all bending with the tube removed from the engine. Adjustment of the fit may be accom- plished  by  bending  by  hand  at  principal  bends.  In  the event the tube cannot be bent by hand, the tube must be  clamped  in  a  fixture  or  device  which  will  not  scratch, indent, crimp, or mark the surface of the tube during the bending operation. The flattened effect of the cross section of the tube as a result of the reforming opera- tion must not exceed 15 percent of the tube OD. d. When   proper   free-state   alignment   is   attained complete  the  tubing  installation  by  simultaneously securing  the  coupling  nuts  and  tightening  them  to proper torque. Always use a backup wrench on the tube fittings when tightening the tube coupling nuts. e. When  a  component  to  which  rigid  tube  assem- blies are attached is replaced, remove all interfering tube  assemblies  to  permit  easy  removal  and  reinstalla- tion of the component. This precaution will prevent subsequent  damage  to  the  tube  assemblies. Change 14 5-2.1(5-2.2 blank)