[aj.lec]

from the MB-C1 manual

FRAME—J - 2
Use of heat is not permissible when straightening frames. Heat weakens structural characteristics of the frame members and all straightening should be done cold. Frame members which are bent or buckled sufficiently to show strains or cracks after straightening, should be replaced.

CUTTING, REINFORCING, RIVETING AND WELDING
Whenever it is necessary to remove or cut the frame, the rail should be cut at an angle of 45 degrees, in other words, make the actual cut twice the width of the rail. This method distributes the cut and weld over a greater area than a cut made at right angles with the rail.
Reinforcements can be made with fiat, channel, or angle stock. Because of difficulties encountered when inserting the channel reinforcements into the frame side rails, the use of angle reinforcements is recommended. Wherever possible, the reinforcement should extend the entire length of side rail or at least 18" beyond the cab cross-member. This procedure, of course, is impractical in many instances because of the position of attached units and existing cross-members. The reinforcement stock thickness should be securely riveted together. Hot rivets are recommended, as they can be properly driven with hand tools. Cold rivets are not recommended unless heavy power press equipment to obtain secure fastening is available.
In addition to thoroughly welding a cut in the side rail, the outside edges of reinforcements should be welded to the frame after the reinforcements are riveted. All unused holes should also be filled with welding material. The welding rod should be substantially the same material as used in the frame.
The diameter of the reinforcement rivets, depends upon the spacing and the number of rivets used. Generally, the rivets are 50% to 100% as thick as plates to be riveted.