Chapter 22 Replacing Structural Parts and Rust Protection

Objectives List the parts of the vehicle that are considered structural List the steps necessary for replacing a part along factory seams Describe how spot welds are separated Explain how new body panels can be positioned on a vehicle List the steps for welding new body panels in place

Objectives (continued) Describe how to install foam panel fillers Section rails, rocker panels, A- and B-pillars, floor pans, and trunk floors Define rust and describe the common factors in its formation Identify the principal methods of rust protection Choose the correct antirust materials and equipment List common types of seam sealers and explain where each should be used

Introduction Most collisions involve some parts replacement Structural parts: –Support the weight of the vehicle –Absorb collision energy –Absorb road shock Examples of structural parts include front rails, strut towers, rocker panels, rear rails Restoring rust protection is a vital aspect of collision repair

Repair or Replace Guidelines Decision to repair or replace a structural part is based on the judgment and skill of the technician/appraiser –If the part is bent, repair it –If the part is kinked, replace it Whenever possible and practical, the part should be repaired rather than replaced

Types of Structural Replacements Sectioning involves cutting the part in a location other than a factory seam When planning to section a structural part –Check the body repair manual for specific sectioning recommendations –Follow the general guidelines presented here if specific sectioning recommendations do not exist A sectioning location should have a uniform area with enough clearance to do welding operations

Determine Spot Weld Locations Remove the paint, sealer or other coatings covering the joint area to find spot welds Paint can be removed with a coarse scuff wheel, mounted in an air tool –Can be removed by heating the paint film, and using a coarse wire wheel or brush Scrape off thick portions of primecoating or seam sealer before scorching the paint If the spot weld locations are not visible drive a chisel between panels to reveal the spot welds

Separating Spot Welds Do not cut into the lower panel if it is to be used Be sure to cut out the spot welds without creating an excessively large hole After the spot welds have been removed drive a chisel between the panels to separate them Do not cut or bend the undamaged panel A chisel should never be used by itself because it will damage adjacent panels

Figure Grind off small nuggets from existing spot welds so flanges on the existing panels are smooth and clean.

Separating Continuous Welds Panels may be joined by continuous MIG welding Since the welding bead is long, use a grinding wheel or cutoff tool to cut through the weld Do not cut into or through undamaged panels Hold cutoff tool at a 45-degree angle to the joint After grinding through the weld, use an air chisel to separate the panels

Preparing Vehicle for New Panel Always refer to the appropriate body repair manual for the type and placement of welds Grind off the welding marks, and use a wire brush to remove dirt, rust, paint sealers Remove paint and primecoating from the backsides of the panel joining surfaces on parts that will be spot welded during installation Smooth mating flanges with a hammer and dolly Apply weld-through primer where bare metal is exposed

Figure After removing the damaged panel, straighten the flange on the other panels so they will fit against the new panel properly.

Preparing Replacement Panel/Part Primer coating must be removed from flanges to allow the welding current to flow properly Use a disc sander to remove paint from both sides of the spot weld area Drill holes for plug welding and apply weld- through primer to the welding surfaces Be sure plug weld holes are the right diameter If the new panel is sectioned to overlap existing panels, rough cut the new panel to size

Positioning New Panels Improperly aligned panels will affect both the appearance and quality of the repaired vehicle Use a measuring system to determine the installation position Panel alignment marks can be provided to help position parts before welding Use locking pliers or self-tapping screws to hold the part in place All straightening must be done before replacing panels

Figure Fit the new panel into position on the vehicle. Locking pliers are initially used to hold it in place.

Welding New Panels/Parts When the position and dimensions of the new panel are satisfactory, weld it in place Apply weld-through primer to bare metal surfaces Clamp parts in position and tack weld them Remeasure part positions, weld parts in final position, and grind cosmetic weld surfaces Important to exactly duplicate the location and number of original factory spot welds

Figure Continuous welds are needed on the exposed surfaces of the replacement panels. Avoid excessive heat buildup that will warp sheet metal.

Sectioning In some repairs sectioning of parts may be required to make repairs economically feasible The configuration of the part being sectioned might call for a combination of joint types Lap joints are used for flat or hat channel shaped parts When welding lap joints, use plug welds in the overlap area, and weld from the top piece down Close the bottom edge with a continuous weld bead; apply seam sealer to joints in floor pans

Figure Note these common sectioning areas on a vehicle.

Sectioning (continued) Butt joint with insert is used on closed sections The insert is made from a section of the replacement or damaged part Do not put inserts in collapse/crush zones; this will change the way collision impact is absorbed Front rail sectioning using a butt joint with insert follows a twelve-step process Do not throw away any parts until repair is done

Sectioning Rocker Panels Two joints most commonly used are a butt joint with insert or a lap joint Use a butt weld with insert when installing a recycled rocker panel with B-pillar attached Multiple part rocker assembly has several pieces of sheet metal with internal reinforcements Reinforcements make it difficult to use inserts

Sectioning A-Pillars A-pillars can be sectioned using a butt joint with insert or an offset butt joint On multiple-piece pillars the design of the par will guide repair planning Reinforcement locations vary, so refer to a body repair manual to properly plan the repair Use an insert if the design of a multiple-piece pillar allows Sectioning an A-pillar is similar to other closed sections and follows a ten-step process

Replacing Foam Fillers Foam fillers add rigidity and strength to structural parts, and to reduce noise and vibrations Cutting and welding will damage the foam filler, and it must be replaced Follow manufacturer recommendations for replacing or sectioning foam-filled panels When parts come without foam filler use a product designed specifically for this application Single-part urethane foams for home use cannot be used for replacing automotive foam fillers

Sectioning Floors Floor pans and trunk floors are sectioned using lap joints Critical to completely seal the joints to keep moisture and exhaust gases out of the passenger compartment Do not cut through reinforcements or critical areas such as seat belt anchoring points When sectioning, the rear section always overlaps the front section so that road splash will not strike the joint head on

Full Body Sectioning Full body sectioning is replacing the entire rear section with the rear section of a salvage vehicle –Requires highest-quality workmanship possible Jigs are used on any sectioning procedure where an offset butt joint is used Full body sectioning requires sectioning the two A-pillars, two rocker panels and the floor pan Complete disclosure must be made to the vehicle owner

Replacing Adhesives Some vehicle manufacturers use structural adhesives along certain weld seams Weld-bond adhesives ad strength and rigidity to the vehicle body and improve rust protection Some manufacturers use structural adhesives in place of welds, such as around wheel openings –Different type of adhesive than weld-bond Check the repair manual for information on the use of structural adhesives

Rust (Corrosion) Rust, or corrosion, is a chemical reaction called oxidation formed when oxygen, exposed metal and moisture are present Stable metal and oxygen atoms break down into ions, which combine to form metal oxides An electrolyte, usually moisture, is a necessary ingredient for oxidation Moisture is controlled by applying coatings to metal, but these break down with exposure

Rust Protection Corrosion protection breakdown falls into three general categories: paint film failure, collision damage, repair process During a collision, the protective coatings are damaged in areas of direct, and indirect damage Preserve the original coating when possible Use conversion coatings to create a zinc phosphate coating on a steel surface Use weld-through primers on bare steel in weld areas

Corrosion Protection Safety Epoxy systems can irritate skin –Wear gloves and avoid skin contact If skin contact occurs, wash with soap and hot water and apply a skin cream If adhesive contacts eyes, wash immediately with clean water for 15 minutes and consult a physician Spot welding in weld-bond joints can generate gases that are harmful if inhaled

Anticorrosion Materials Anticorrosion compounds should be applied to the underbody or inside body panels Seam sealers prevent the penetration of water, mud and fumes into panel joints Weld-through primers are used between the two pieces of base metal at a weld joint Corrosion converters change ferrous iron oxide into ferric iron oxide and may contain a latex emulsion that seals the surface

Applying Corrosion Protection Materials Keep the material away from parts that conduct heat, electrical parts, labels and identification numbers, and moving parts For exposed joints and seams, thoroughly clean the seam and apply primers and seam sealers Apply the final primer coats and paint For exterior underbody surfaces, clean the area Prime with self-etch or epoxy primer and apply sealer and paint to primed areas

Summary Structural parts support the weight of the vehicle, absorb collision energy, and absorb road shock Repair versus replacement: –If the part is bent, repair it –If the part is kinked, replace it Sectioning involves cutting and replacing panels at locations other than at factory seams

Summary (continued) Sectioning rails, pillars, and rocker panels may be required for economic feasibility Full body sectioning is replacing the entire rear section of a collision damaged vehicle with the rear section of a salvage vehicle –May be more economical than trying to rebuild a damaged vehicle with new parts Corrosion breakdown categories: Paint film failure, Collision damage and the repair process