Saturn Front Unirail Section Procedure

As with the rear unirail section procedure outlined in Tech-Cor Bulletin 1993-6, the subject of reparability of the Saturn will also be the focus of this particular bulletin. The following text will describe a section procedure for the left front unirail that includes replacement of the rail extension (or closure panel) and also the lower tie bar.

The collision energy management characteristics of this vehicle often confines the damage to the front of the unirail. Although the damage may not be repairable due to the amount or degree of deformation, complete replacement is often unnecessary and/or impractical.

A section joint employing an overlap has been designed to permit partial replacement in the area under the radiator side support baffle, slightly forward of the engine cradle mounting point.

Although the unirail section described in this bulletin was performed on the left side of the vehicle, the procedure applies to the right side as well.

The space frame must be returned to its proper dimensions through appropriate pulling methods, prior to removal of any damaged structural components.

After pulling operations have been completed, the lower tie bar that is welded to the front rail extensions must be removed to gain proper access. Refer to Photograph 1.

The side support baffle that joins the rail to the radiator support is also removed by drilling out the attaching spot welds. If this support panel is not damaged, it can be reused. Refer to Photograph 2.

The rail extension/closure panel that is attached to the outside portion of the unirail is removed by drilling out the spot welds.

Refer to Photograph 3. This is necessary to expose the C-channel portion of the damaged rail where the section joint will be located.

Both the damaged and replacement rails are cut straight through. The replacement closure panel is purchased separately from the rail and is attached after the replacement inner rail section is welded in place.

The damaged rail is cut 4 inches (101.6 mm) forward of the leading edge of the oblong hole that is stamped in the underside of the rail. The replacement inner rail is measured from the same location, but is cut 3 3/4 inches (95.3 mm) forward of the oblong hole to allow for a maximum of 1/4 inch (6.4 mm) overlap at the section joint.

When the replacement inner rail section is clamped in place, the overall measurement should be 10 3/8 inches (263.5 mm) from the leading edge of the rail to the leading edge of the oblong hole located on the bottom side of the existing rail, slightly rearward of the engine cradle mounting bolt. Refer to Photographs 4 and 5.

After fit-up of the replacement section, proper dimensions should be verified prior to welding.

The inner rail section is attached by lap welding all three sides. For all other welding, such as the rail closure panel and radiator side support baffle, use the MIG plug method. To eliminate overhead welding, the replacement inner rail section is welded on the inside at the bottom portion of the C-channel, and on the outside of the C-channel on both the side and top mating surfaces.

The exposed seam on the underside of the rail section joint should then be caulked to ensure proper corrosion protection. Refer to Photographs 6 and 7.

Refer to the Welding Information section of this bulletin for general welding guidelines.

As noted in the Saturn Rear Unirail Section Bulletin 1993-6, and also mandated in the Saturn Body Repair Manual, a two-part epoxy primer such as PPG DP90/DP401 Catalyst, or an equivalent product must be used on all bare metal surfaces to achieve proper corrosion protection, and also to match the color of the coated structure.

After the replacement inner rail section has been welded in place, the inner portion of the rail at the section joint should be prepared and primed before the closure panel is attached. Refer to Photograph 8.

The closed portion of the sectioned rail should also be primed using a wand, then coated with an anti-corrosion compound. Refer to Photographs 9 and 10.

Welding Information

Prior to any welding operations, the weld site must be cleaned to remove grease and dirt as well as primers and paint, without removing factory corrosion protective coatings or thinning the base metal. Do not remove any preexisting galvanized coatings. Do not use an oxyfuel (oxyacetylene) gas torch. After cleaning, a weld-through coating must be applied to all bare metal in the overlap area of the weld sites. All welding should be performed with a M.I.G. welder (Metal Inert Gas, now called G.M.A.W. or Gas Metal Arc Welding). Welding wire should be either 0.023" (0.584 mm) or 0.025" (0.635 mm) diameter which meets or exceeds the American Welding Society Standard (AWS-E-70S-6) with a mixture of 75% argon and 25% carbon dioxide shielding gas. Do not concentrate all welding efforts on one area, but alternate sites so that each welded area has time to cool down before the welding is continued. All continuous welds must be made in 1/2" - 3/4" (13-19 mm) increments which helps to minimize heat build up which can cause metal strength loss and/or panel distortion. The welding equipment must also be properly adjusted by making and testing practice welds on similar materials.

Corrosion Protection, including the refinishing of replacement components should be performed as outlined in Tech-Cor Bulletin 1986-7, Restoring Corrosion Protection During Vehicle Repair.

The information provided in this bulletin is for educational purposes only. Although every effort has been made to ensure the accuracy of the information contained in this bulletin, Tech-Cor assumes no responsibility or liability for any repairs performed using information from any publication issued by Tech-Cor.

Any person performing repairs must determine whether any suggested or recommended procedures or repairs are suitable or appropriate for the particular vehicle being repaired. The repairer remains solely responsible for such determination, as well as for the proper completion of the repairs.

Reproduction of this bulletin is not permitted without the written approval of Tech-Cor.