Notice: Do not heat the frame beyond 606° C (1200° F). Overheating will cause distortion and stretching, as well as a change in the characteristics of the metal.
Frame straightening may be a complicated process and usually requires some special equipment. Only trained technicians should perform a frame straightening procedure.
Conduct a complete analysis of the frame condition before beginning the straightening process in order to determine the correct sequence of steps for the repair procedure. Refer to Frame Conditions and Minimizing Frame Service Description . It is also important to identify the frame material before beginning the repair procedure. Refer to Frame and Underbody Description .
Adhere to the following instructions while conducting the repair procedure:
| • | Apply pressure from different directions in order to reverse the flow of damaging forces. |
| • | Control the temperature and the application of the heat. |
| • | Heat the frame using a large sized tip (multi-hole heating tip) and a neutral flame. Keep the oxygen opened just enough to remove the feathers or the stringers from the blue center at the tip of the torch. |
| • | Heat the area that will be stretched as the frame is straightened. |
| • | Heat the area after exerting sufficient pressure. A slight checking or some silvery cracks will appear on the surface of the metal when heating it at an adequate pressure. |
| • | Gradually increase the pressure while heating the metal. |
| • | A red glow is an indication of overheating. |
Two common types of cracks are shown. The straight crack (1) usually travels from the edge of a flange, across the flange, through the web section of a rail, and through the other flange. A straight crack results from:
| • | High concentrations of stress in small areas of the frame |
| • | Excessive bending movement |
| • | Torsional loading |
The sunburst crack (2) radiates from a hole in the web section of a rail or a crossmember. Heavy loads and a loose mounting bracket or crossmember can cause a sunburst crack.
If both the rail and reinforcement are cracked in a particular area of the frame, repair them separately. Flanges must react independently in order to prevent localized stress.
Use a copper spacer between the flanges of cracked base rail flanges and reinforcement flanges.
Repair the crossmember mounting flange crack in the same manner as the side rail crack. But you should build up weld bead to provide a good, smooth radius. Replace a badly damaged crossmember.
You may have to align the frame and level the rails before you repair the frame.
