An inexpensive alternative to buying pre-bent pipes, bending exhaust pipes yourself allows you to replace a leaking or rusted pipe quickly and efficiently. Bending your own exhaust pipes ensures the best fit possible, because you adjust the bends as required, creating the custom fit needed. Improper bending of exhaust pipes, especially when making tighter bends, can ruin the pipe by causing it to crease at the point of the bend. There are two ways to prevent pipe creasing, mandrel bending and filled-pipe bending. Filled-pipe bending is easiest with shorter pipes.
Measure the length of the pipe to the bend. On 90-degree bends, measure this as the distance from the end of the previous pipe to where you want the far wall of the pipe after the bend. For smaller bends, this is where you want the change in direction to begin. Add two to three inches for pipe connection overlap where the pipe clamp connects. Mark this distance on the pipe slated for bending.
Locate the diamond or triangle mark on the bender mandrel and line up the point of this mark with the mark you measured and made on the pipe.
Bend the pipe until it reaches the desired bend angle. Remove the pipe from the mandrel.
Hold the pipe in place to verify proper fit and adjust as necessary to provide the custom fit desired.
Perform the same measurement and marking as in Step 1 for mandrel bending.
Pack the pipe tightly with sand and cap both ends of the pipe. There must be enough pressure in the pipe to prevent the walls of the pipe from collapsing when you make the bend. Put the welding gloves on.
Clamp the exhaust pipe firmly in the vice, with the mark you made in Step 1 just visible at the vice. Light the torch following the directions that came with it, heat the pipe at the point of the bend until pliable, and pull the pipe towards you to make the bend.
Remove the pipe from the vice and hold it in place to check its fit and adjust your bend as necessary.
Remove the caps from the pipe and flush the pipe with water.
Another form of filled-pipe bending uses a heavy-duty spring placed over the outside of the pipe at the point of bending. Both methods require some effort to bend the pipe. Bend the pipe in degrees to ensure that the pipe bends exactly where you need it. A combination of filling with sand and using the outer coil spring provides the best results when using a vice to keep the pipe clamped in place.
No matter which method used, mandrel or filled-pipe, bend the pipe slowly to decrease chances of kinking the pipe.