Preliminary Requirements

Procedure

1. SUBTASK 70-41-00-400-001 General Torque Tightening Information

   1. NOTE

      The torque values specified in technical manuals have precedence and must always be used. Where no special torque values are given, use the standard torque values given in the SPM TASK 70-41-01-400-501.

      General.

      1. This procedure gives general information only for the torque tightening of fastenings and should be read with TASK 70-41-01-400-501 (SUBTASK 70-41-01-860-400-001) which describes the process of torque tightening in more detail.

      2. Before you start the task, consider the number of fasteners to be tightened and the form of the joint. Select a suitable wrench with an appropriate load scale because of the difficulty in reading accurately the load in the first and last quarter of the load scale.

      3. For a small number of bolts at moderate torque loads (for example, 3 or 4 bolts at up to 125 lbf/inch), use a suitable manual wrench; the use of a power tool is not appropriate.

      4. Due to the introduction of variable speed control on many power tools, the required accuracy in bolt tension cannot be achieved by power wrenching. Therefore with the specific exceptions given in the SPM TASK 70-41-01-400-501, do not use a power wrench for final torque tightening of nuts, bolts, etc.

      5. Do not use power tools to tighten fastenings joints that contain "crush gaskets" because you could damage the gasket can be damaged by an inappropriate tightening technique.

         1. The torque values contained in this and related documents, must be specified as follows:

         2. 1. Torque values in lbf/inch (Nm).

            2. Angles of turn in degrees.

            3. Extension values in inch (mm).

         3. The torque values used for J-threads are the same as those used for standard screw threads.

   2. When a part to be torque tightened is hot, give sufficient time for it to decrease to a temperature equal to that of its adjacent parts before it is fully torque tightened.

   3. Mating of Parts.

      1. The joints between flanges, or between mating surfaces, must be very carefully made during the assembly. When snap-fit joints are made, the mating surfaces must be correctly engaged before the full torque value is applied. All parts and mating surfaces to be torqued must be free from all debris, outside contamination, and material not approved/specified in technical documents.

      2. Unless a special procedure is given in the assembly instructions bolts must be equally tightened so that individual bolts and/or the flanges do not become locally stressed until full torque value is achieved.

      3. All torque values must be applied slowly and smoothly to get the most accurate and constant results. There will be times when the specified torque values can not be applied. At such times, an accurate analysis must be made to find the correct torque value to be applied.

      4. It is preferred that the nut, rather than the bolt, be turned wherever possible.

         1. If it is necessary to turn the bolt rather than the nut, then the conditions in the subsequent list are applicable:

            1. The bolt (this includes close tolerance shank bolts) must pass freely through the aligned holes of the mating parts.

            2. Where the material of the part that mates with the bolt head bearing surface is soft (such as aluminum and magnesium), it is necessary to use an Engineering-specified washer between the part and the bolt head bearing surface.

            3. The bolt head bearing surface must be lubricated.

      5. Hold tubes so that they do not twist when the connector is tightened or loosened.

   4. Lubrication.

      1. The use of a lubricant is very important to get the correct bolt tension because most of the torque becomes friction at the nut and bolt bearing surfaces and screw threads. Unless specified differently, the given torque values only apply when the screw threads and bearing surfaces are correctly lubricated with clean engine oil to an approved specification.

   5. Castellated Nuts.

      1. When minimum torque values are given for castellated nuts, they must be tightened to the specified limits; then, if necessary, tightened again to align the lock-slot.

      2. When minimum and maximum torque values are given for castellated nuts, again align the lock-slot but do not tighten the nuts by more than the maximum limit. If this is not possible, a different nut must be used.

   6. Definitions.

      1. Self-locking or prevailing torque.

         The torque necessary to overcome kinetic friction between the fastener mating threads with the locking element fully engaged and with no axial load on the assembly.

      2. Breakaway torque.

         The torque necessary to overcome static friction between the fastener mating threads with the locking element fully engaged and with no axial load on the assembly.