ALUMINUM BODY PANEL REPAIR PROCEDURE DIFFERENCES

MODELS AFFECTED: 1987 ALLANTE

Allantes have three exterior aluminum panels: the hood, deck lid and removable hardtop. Repair procedures for these panels vary significantly from sheet metal.

Although the customary method of rough out and fill with plastic filler will work satisfactorily; heat shrinking, use of heat as a corrective force, metal finishing and the welding process are quite different. These differences are as follows:

1. Heat Shrinking -------------- The procedure for heat shrinking aluminum is the same as steel except aluminum melts at 1200 DEG F and does not change color prior to melting, where as steel melts at 2700 DEG F and changes to a cherry red color before melting.

2. Heat As A Corrective Force -------------------------- Sheet aluminum expands rapidly when heated; the rate of thermal expansion for aluminum is approximately four times greater than steel. This process is of great value for raising low spots of the elastic type during metal finishing, or when removing hail stone damage.

3. Metal Finishing --------------- During normal metal finishing operations, nothing more coarse than #80 grit disc should be used on aluminum. The exception to this rule would be initial paint removal. In this case, use #36 open coat disc.

When filing aluminum, the file should be cleared of chips continually to avoid gouging that file chips create when trapped in the file teeth. The outside edges of the body file should be disc sanded to prevent the sharp edges from gouging the aluminum.

4. Welding ------- Any of the following methods can be used to weld aluminum:

o GMAW - Gas metal arc welding (MIG) o GTAM - Gas tungsten arc welding (TIG) o RSP - Resistance spot welding o OXY - Acetylene welding

When aluminum surfaces are exposed to the atmosphere, a thin invisible oxide skin forms immediately which protects the metal from further oxidation. This self-protecting characteristic gives aluminum its high resistance to corrosion. This oxide has a melting point of 3700 F, far above the 1200 F melting point needed for welding. Therefore, this oxide must be removed with a stainiess steel wire brush just prior to welding.

Local G. M. Training Centers are presenly offering an in-depth one-day automotive sheet aluminum repair course (#22003.70) for the experienced body repair technician on the repair and welding of aluminum.

It is highly recommended that body shop technicians be enrolled in this training course.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.