I-CAR Non-Structural cheat sheet

Unibody construction uses welded box sections and rails to carry loads; the outer panels on most unibody vehicles are non-structural cosmetic or minor-stiffening members.

Body-over-frame (full frame) vehicles carry crash and payload loads in a separate ladder frame; body mounts isolate the cab and box, so frame straightening precedes body panel alignment.

Spaceframe and aluminum-intensive structures use extruded sections, castings, and rivet-bonded joints; heat from welding or sustained torch heating can anneal or distort these alloys.

Mild steel has low yield strength and is highly formable; high-strength steel (HSS) and ultra-high-strength steel (UHSS) resist forming and require controlled heat and specific weld schedules.

Boron and martensitic UHSS grades commonly appear in rockers, B-pillars, and roof rails; OEM procedures typically prohibit heat and sectioning in these zones.

Collision energy management depends on controlled crush zones and a rigid occupant safety cage; straightening a crush zone back to shape does not restore its engineered crush characteristics.

Repair decisions hinge on the OEM body repair manual: it defines sectioning locations, weld types, adhesives, and metal grades for each panel.

Vehicle identification and materials mapping begin with the VIN, door jamb labels, and OEM service information, not with visual appearance alone.

Locate and record all attachment methods before removal: welds, rivets, structural adhesive, bolts, clips, and seam sealer all appear on modern outer panels.

Drill spot welds with a spot-weld cutter matched to weld diameter; cutting through both layers creates an oversized hole that weakens the new weld.

When separating adhesively bonded panels, apply controlled heat within the OEM temperature limit and use a blade or wire to avoid stretching the substrate.

Flange preparation includes removing residual adhesive and weld nuggets, restoring flange flatness, and applying the OEM-specified primer or coating.

Trial-fit the new panel with all gaps and flushness checked before permanent attachment; adjustment after welding or bonding is far more limited.

Panel gaps are measured with a gap gauge at consistent reference points and compared to the opposite side or OEM specifications.

Hood and deck lid alignment sequence: set hinges and rear edge first, then front corners, then latches and strikers.

Doors align by adjusting hinges for the rear gap and beltline, then the striker for flushness; never force a striker to compensate for hinge misalignment.

Steel has a memory: after rough straightening, relieve stress with controlled hammer-on-dolly work before finishing, or the panel will oil-can.

A crown or low spot is identified by sighting along the panel or by the reflection method; a straightedge reveals high spots as rocking contact.

PDR (paintless dent repair) applies to accessible dents with intact paint and no stretched metal; sharp creases and stretched crowns require conventional repair.

Heat shrinking is used on stretched steel only; overheating discolors and softens the panel, and aluminum loses strength at far lower temperatures.

Aluminum panels work-harden and crack with repeated bending; use dedicated aluminum tools to prevent galvanic cross-contamination with steel.

Plastic bumper covers are repaired with plastic welding or flexible filler matched to the substrate identification code molded into the part.

Sand scratches from coarse abrasives telegraph through topcoat; finish repairs with the OEM-recommended grit progression before priming.

Repair versus replace is decided by OEM position statements and by whether the panel's structural or appearance function can be restored within specification.

Squeeze-type resistance spot welding (STRSW) is the preferred method for matching factory welds on steel panels; weld nugget quality depends on clean mating surfaces and correct electrode force.

MIG brazing joins galvanized and HSS panels with lower heat input than fusion welding; it is not a structural fusion weld and must not be substituted where the OEM specifies a full weld.

Plug welds made in an oversized hole are common where a squeeze welder cannot reach; hole diameter and weld count follow the OEM weld schedule.

Adhesive bonding distributes load across the entire flange and is often combined with rivets or welds for fixturing until cure; bondline thickness is controlled by glass beads or spacers.

Adhesive cure time and temperature follow the product technical data sheet; moving or loading the joint before full cure causes creep and bond failure.

Galvanic corrosion occurs when aluminum and steel contact; use OEM-specified isolation coatings, barriers, and dedicated fasteners at mixed-metal joints.

Weld-through primer protects the mating flange but must be applied thinly and only where the OEM permits, since excessive primer degrades weld quality.

After attachment, restore corrosion protection on all heat-affected and bare-metal zones before seam sealing.

Body filler is applied only over properly prepared, primed bare metal or OEM-approved substrates, never directly over paint, e-coat scratches, or rust.

Filler thickness limits follow the product data sheet; deep repairs require reshaping the panel first, not building thickness with filler.

Polyester glazing putty is for minor imperfections only and is not a substitute for filler or primer over large areas.

Two-part epoxy primer provides corrosion protection and adhesion on bare steel and aluminum; self-etch primer is used where the OEM specifies it for bare metal.

Cavity wax or inner-panel coating is applied to enclosed box sections after welding or sectioning, since exterior coatings cannot reach interior surfaces.

Seam sealer replicates factory seams and prevents water intrusion; it is applied over primed surfaces and tooled to match OEM appearance and coverage.

Sealer and coating products must be compatible with the topcoat system; silicone contamination causes fisheyes and adhesion loss.

Corrosion protection is verified visually and documented: bare metal, weld zones, hem flanges, and cavity areas each require coverage.

Bolted panels such as fenders, doors, and hoods are located by adjustable hinges and shims; record shim locations and counts before removal.

Threaded fasteners in aluminum or thin-gauge steel are torque-limited; use a torque wrench and the OEM specification to avoid pulled threads.

Fasteners with thread-locking compound or torque-to-yield characteristics are replaced, not reused, per OEM direction.

Door and hood hinge wear shows as sag or uneven gaps; hinge replacement precedes gap adjustment on the new panel.

Removable panels on body-over-frame vehicles may require body mount inspection before alignment, since frame or mount damage shifts the entire body.

Electrical and mechanical content (window regulators, latches, wiring harnesses) transfers to the new panel and is function-tested before trim installation.

Clips, retainers, and weatherstrips are typically one-time-use items; reuse causes wind noise, water leaks, and rattles.

Final check includes latch operation, flushness, gap uniformity, and water test where the OEM or shop quality plan requires it.

Urethane-set windshields contribute to roof crush resistance and passenger retention; the OEM bead width, location, and urethane type must be matched.

Urethane cure time before vehicle release follows the adhesive manufacturer's safe-drive-away specification, adjusted for temperature and humidity.

Glass primed with the correct primer system is required for adhesion; contaminated or unprimed frit causes bond failure.

ADAS cameras and sensors mounted to the windshield require recalibration after glass replacement; the mounting location and bracket must match the original.

Interior trim removal uses plastic trim tools and clip release sequence; metal tools gouge substrates and break retention clips.

Airbag-equipped seats, pillars, and headliners require battery disconnect and OEM wait time before service near inflators.

Side and rear glass with defrosters or antennas requires continuity checks after installation.

Water leaks are traced with controlled water testing at seams, glass beads, and body plugs, then sealed with OEM-approved materials.

Plastic parts carry an identification code molded into the back side; repair method, filler, and adhesive are selected from that code.

Thermoplastic fascia can be plastic-welded with rod material matching the substrate; thermoset plastics cannot be welded and require adhesive repair.

Flexible additive systems in bumper topcoats allow movement without cracking; rigid primer on flexible plastic leads to cracking and peel.

Adhesion promoter is required on many plastics before primer; skipping it causes coating delamination.

Bumper energy absorbers and reinforcements are one-time-use crash components on many vehicles and are replaced rather than straightened.

Sensor and camera openings in fascias must retain exact geometry; repair material buildup around sensor bores can block radar or ultrasonic function.

Repair limits are defined by the OEM and by the part's function; structural bumper beams and mounting areas generally are not repaired.

Post-repair inspection confirms clip retention, gap to adjacent panels, sensor fit, and coating flexibility.

ADAS features include forward collision warning, automatic emergency braking, lane departure warning, blind spot monitoring, adaptive cruise control, and rear cross traffic alert.

Radar sensors align to vehicle centerline and are sensitive to bumper cover thickness, coatings, and repair materials over the sensor face.

Camera-based systems require a clear field of view through the windshield; incorrect glass, tint, or mounting bracket position degrades performance.

Recalibration is required after windshield replacement, bumper replacement, suspension or ride height changes, wheel alignment, and sensor removal or replacement.

Static recalibration uses targets at specified distances in a controlled space; dynamic recalibration requires driving at specified speeds and conditions.

Pre-repair scanning identifies stored diagnostic trouble codes and system faults; post-repair scanning confirms no new codes after calibration.

Battery disconnect and OEM wait times precede work near airbags, pretensioners, and inflators; SRS components are not repaired or reused after deployment.

Documentation of scan results and calibration completion is part of the repair record and supports liability protection.

OEM repair procedures are accessed through the manufacturer's service information site by VIN; position statements define what the OEM permits.

Pre-repair and post-repair scans are documented with the tool used, codes found, and actions taken.

A repair record includes VIN, mileage, panel identification, materials, attachment methods, products used with batch numbers, and calibration results.

Sectioning locations, weld counts, and adhesive part numbers are recorded so the repair can be verified against the OEM procedure.

Quality control checks include gap and flushness measurement, coating thickness, corrosion protection coverage, and function tests of all disturbed systems.

Measuring systems verify dimensional accuracy against OEM datum specifications before and after structural pulls.

Supplement requests are supported by documented findings such as hidden damage, scan results, and OEM procedure requirements.

Final delivery documentation includes calibration confirmations, scan reports, and any customer disclosures required by the shop or insurer.