Straight cracks (1) and sunburst cracks (2) are the 2 common types of cracks found in a frame.

A straight crack usually starts from the edge of a flange, spreads across the flange, goes through the web section of the rail, and then continues through the other flange. A straight crack results from stress concentrations, excessive bending movement, and torsional loading.

A sunburst crack radiates out from a hole in the web section of a rail or a crossmember. Applying a high load at a mounting bracket or a crossmember that is not securely attached to the rail may cause a sunburst crack.

If the rail and the reinforcement both crack at a particular area of the frame, repair each part separately. The flanges must react independently in order to prevent a localized stress concentration. Use a copper spacer between the flanges of cracked base rail flanges and cracked reinforcement flanges.

Use the same procedure for a crack in the crossmember mounting flange as for a crack in the side rail. However, when repairing a crack in the crossmember mounting flange, build up the weld bead in order to provide a smooth surface. Replace any damaged crossmembers.

You may need to align the frame and level the rails before repairing the frame.

Use the following procedure in order to repair a crack in any rail, reinforcement, or crossmember that is not made of a heat-treated steel:

1. Remove any equipment inhibiting access to the crack.
2. Drill a 6 mm (0.23 in) hole in the extreme end of the crack.
3. V grind the entire length of the crack from the starting point to the 6 mm (0.23 in) hole in the extreme end. The angle of the V depends on the type of welding process that is used.
4. Open up the bottom of the crack 2 mm (0.07 in) in order to allow an adequate penetration of the weld using a hack saw blade.
5. Weld the crack with the appropriate electrode and welding technique.
6. Grind the weld until it is smooth on the inside and the outside of the rail or the crossmember. Remove any weld build up or notches on the edge of the flange.

Reinforcements increase frame strength by increasing the section modulus of the reinforced area. An effective reinforcement must compensate for any factors that could cause damage to the frame, while not introducing any new factors that may cause stress concentrations. While a reinforcement is intended to make the frame (1) less flexible, an excessively stiff reinforcement may cause frame failure.

Adhere to the following guidelines when selecting the type or length of a reinforcement:

Any incorrect (1) reinforcement practices may cause abrupt changes to the section modulus.

Follow the correct (2) reinforcement practices carefully to avoid any frame damage.

The following types of reinforcements may be combined in different ways to meet any special needs, such as heavy demands:

•	Use an inverted L reinforcement on either the inside or the outside of the frame rail. Use the inverted L reinforcement where the maximum stress occurs on the upper flange and where the frame or hanger-bracket design does not allow the use of an upright L reinforcement.

•	Use channel reinforcements on the inside or the outside of the frame rail in order to reinforce the flange and the web rail.

•	Use web reinforcements, plug welded at 200-500 mm (7.87-19.68 in), on the inside of the rail web.

•	Use strap reinforcements, plug welded at 150-200 mm (5.9-7.87 in) intervals (1), on the rail flange on the inside of the channel. Do not weld across the end or along the edges of the reinforcement.

•	Use fish plate reinforcements on the outside of the rail web, extending above or below the rail, to stiffen the frame.

•	Use an upright L reinforcement on the inside or the outside of the frame rail. Use an upright L reinforcement where the maximum stress occurs on the bottom of the lower flange.

•	Use inverted J reinforcements, attaching only to the web section, on the inside of the rail channel. The inverted J reinforcement is designed to prevent any flange buckling due to high torsional inputs or shock loading during a tractor hook-up operation.

Observe the following practices when creating a reinforcement of any type:

Attach all reinforcements with rivets or, preferably, bolts. In some cases, welding may be acceptable. For example, a plug weld is used on a strap or a web reinforcement. It is acceptable to ream an enlarged or irregularly worn bolt hole in order for it to accept the next larger bolt diameter. Body-fit bolts with hardened washers may be used on critical areas. When using a body-fit bolt, ream the hole to a non-standard size to get an interference fit for the bolt. Use existing holes whenever it is possible. If you need to make new holes, use a cobalt high-speed drill. Sharpen the drill to give a 150 degree inclined angle with a lip clearance of 7-15 degrees. Avoid enlarging a pilot hole in successive stages and also avoid breaking through to the full size at the bottom of the hole. Remove the lip of a hole with a reamer. Observe the following guidelines when attaching reinforcement: