Replacement of damaged panels

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Damaged panels can be removed from vehicles by

using:

1 A hacksaw and metal cutting snips

2 A hammer and thin narrow-bladed chisel

3 Either a conventional drill, a Zipcut tool, or a

spot-welding removal tool (air operated) to drill

out each spot weld

4 An air chisel with appropriate cutting tools

5 A power saw having either a rotary vibrating

blade or a straight reciprocating blade

6 A plasma arc cutting torch

7 A combination of any of the above methods.

A severely damaged inner panel such as a wheel

arch can be cut out using the oxy-acetylene torch.

However, this method is not recommended because

of the very ragged uneven cut edge left by the

torch. A better method would be the use of the

plasma cutting torch, which leaves a fine cut edge

for panel replacement. With both of these methods

it is important to be aware of the fire risks.

Lapped and spot-welded joints of panels must be

drilled first and carefully separated with a narrowbladed

cold chisel (Figure 14.95). The positions of

the spot welds are indicated by small circular discolorations

of the metal. These are centre popped,

then drilled 4.8 mm or 5.6 mm sufficiently far to

break the joint; it is not always necessary to go

right through both parts of the panel, as in most

cases if the top panel is drilled the joint will break.

Alternatively a cobalt drill specially designed for

cutting out spot welds can be used, either in a

conventional air or electric drilling machine, or

fitted to an air attachment designed specifically as

a spot-welding removal tool. Another alternative is

the Zipcut tool, which again will fit into a conventional

drilling machine and which cuts round the

spot weld leaving a hole in the top panel surface

(see Figure 14.96). In some cases a fine-toothed

hacksaw blade, fitted in a padsaw handle, and a

pair of snips or shears can be used to remove

damaged sections of panels. A tool for removing

damaged panels is the power chisel set, which

comprises a compressed air gun having interchangeable

chisel heads. This sheet metal cutter

is capable of speedy and accurate removal of

panels or parts of panels that have to be replaced.

Power saws can also be used in the removal of

damaged sections: either the rotary saw with a

vibrating blade, or the straight reciprocating blade

(see Figure 14.97). Both of these tools give an

excellent fine cut edge suitable for instant rewelding

without any dressing.

The bodywork having been straightened and

aligned as much as possible, the new panel should

be positioned and held in place by two or three

clamps and all adjacent panels checked for

alignment with the new panel (Figure 14.98). To

ensure a perfect fit it is often necessary to trim

the adjoining panels of ragged edges, and to

straighten out the locating flanges using hand tools

(Figure 14.99). When making a close butt weld,

exact alignment is ensured by positioning and

clamping the new panel outside the old so that a

scriber can be run down the edge of the old panel

where the joint will come. Excess metal then being

carefully trimmed and the edge dressed up with

hammer and dolly, the new panel is ready to be

458Repair of Vehicle Bodies

Figure 14.93Wheel alignment (Sun Electric UK Ltd )

(a) Front wheel toe

The individual front wheel toe angle A is the angle of the front wheel from the straight overhead. The total

toe is the sum of angles A and B. The term ‘toe-in’ is used when the wheels are closer together at the front,

and ‘toe-out’ is when the wheels are closer at the rear. The purpose of toe is to ensure that the wheels are

in the straight ahead position when driving. An incorrect setting would cause excessive tyre wear.

Major accident damage 459

welded into place. Always brush on weld-through

anti-corrosive primer before welding. The panel

should be aligned, clamped and checked. It should

next be tack welded at several points; then the

clamps should be removed and the panel rechecked

for alignment. If this is not satisfactory the tack

welds are easily broken. When alignment is correct,

further tack welds may be placed between the first

set. To avoid distortion only short sections between

the tack welds should be welded at a time and the

metal allowed to cool (Figure 14.100). In some

(Facing page)

Figure 14.93(continued)

(b) Castor

The castor angle is the forward or backward tilt of the king pin or ball joints, and is measured as an angle

from the vertical. A positive castor is when the top ball joint is behind the bottom ball joint. A negative

castor is the opposite. The purpose of castor is to cause the front wheels to maintain a straight ahead

position and to return to the straight ahead after making a turn. Incorrect castor will not cause tyre wear but

would cause the vehicle to wander on the road and not return to the straight ahead after cornering.

The camber angle is the inward or outward tilt of the wheel when looking from the front of the vehicle. A

positive camber is when the top of the wheel tilts away from the vehicle. A negative camber is when the top

of the wheel tilts towards the vehicle. The purpose of camber is to bring the centre point of the steering in

the centre of the tyre so the tyre turns on one point. This will decrease the effort required to turn the

steering. Incorrect camber will cause the tyres to wear on the inside or outside, heavy steering and poor

directional control.

(d) KPI (SAI)

The KPI or SAI is the angle formed by a line drawn through the king pin or ball joints with a line drawn

vertical. The purpose of KPI is the same as for camber. The KPI will reduce the need for large camber

angles, and therefore reduce the tyre wear by allowing the wheel to be near vertical.

(e) Included angle

The included angle is the sum of KPI (SAI) and camber. The point of intersection of KPI and camber gives

the point about which the wheel rotates when the steering is turned. This point should be in the centre of

the tyre where it contacts the road. Incorrect included angle would cause heavy steering and excessive

tyre wear.

(f) Toe on 20° turns

The toe on turns angle allows the front wheels to follow different arcs when cornering, and is measured

when the inner wheel is at 20° from the straight ahead. The purpose of toe on turns is to allow for the

greater distance of travel of the outer wheel when cornering. Incorrect toe on turns would cause excessive

tyre wear.

(g) Set back

Front wheel set back is the amount that one front wheel is ahead of the other. Excessive set back would

cause the vehicle steering to pull.

(h) Rear wheel reference toe

The front to rear wheel alignment measures the amount of out of alignment of the front and rear wheels. If

the wheels are out of line the vehicle will ‘crab’, which means that the vehicle will appear to be driving

sideways.

Figure 14.94Four wheel alignment: steering wheel

straight ahead (Sun Electric UK Ltd )

460Repair of Vehicle Bodies

cases it is helpful in confining the heat, and thus

reducing the chance of distortion, to place wet cloth

packing either side and a little distance away from

the weld; alternatively there is a foam type of material

which will act as a heat barrier (Section 14.4.7).

Panels that were originally spot welded, but cannot

be spot welded back, can be MIG welded in the

course of repair; the welds are made in the same

place by welding through the holes in the adjacent

panel which were left when the original spot welds

Figure 14.95Drilling out spot welds for the removal

of damaged panels (Motor Insurance Repair

Research Centre)

Figure 14.96Zipcut tool for the removal of spot

welds (Sykes-Pickavant Ltd )

Figure 14.97Cutting out damaged panels with a

power saw (Motor Insurance Repair Research Centre)

Figure 14.98Alignment of new panel sections

(Motor Insurance Repair Research Centre)

Figure 14.99Cleaning up the locating flanges

(Motor Insurance Repair Research Centre)

Major accident damage 461

were drilled out. This method is known as plug

welding. Another method of securing panels is to

MIG braze them in place, but one must remember

that although MIG brazing will cause less distortion

than MIG welding, it is not as strong. Therefore if

the particular panel is a load-bearing panel, it must

be welded in fully to obtain the maximum strength

for the particular panel assembly. MIG welding has

the advantage of reducing distortion to a minimum,

owing to the effect of the inert gas shielding the

spread of heat around the weld zone. This makes

butt joints in panel assemblies more easy to accomplish,

as less dressing up and planishing is required

than in gas welding. Another advantage arises from

the automatic feeding of filler material into the

weld pool, which results in better penetration in all

weld positions. As this equipment can be used both

to weld and to spot weld, it is widely employed as a

means of welding in new panel assemblies.

Partial panel replacement

The reason for replacing only part of a panel

can vary according to the type of repair. Usually it is

quicker and therefore less expensive than full

replacement. If sectioning does not save on time or

money, then the part is completely replaced: that is,

when the repanelling and straightening reaches the

cost of the complete new panel. Some manufacturers

design repair panels specially for these purposes.

Part panel replacement has long been established

as an effective way of repairing body damage on all

cars. Depending on the type of damage involved, it

used to be common practice to replace an entire

sheet metal panel; by means of a part panel repair it

is possible to replace only those panel sections

which are actually damaged. The possibilities for

sectional repairs to load-bearing and non-load-bearing

parts have been taken into account during the

initial phase of development by manufacturers. All

instructions given regarding the locations of cut

lines for sectional repairs to load-bearing parts must

be strictly adhered to. Sectional repairs to vehicles

damaged in an accident should be confined to body

parts in which the damage has not produced any

loss of strength sufficient to jeopardize safety. Only

welding materials reaching the design weld

strength should be used. Moreover, a body alignment

and welding jig must always be used for

repair operations such as sectional replacement of

the sidemember/apron-panel assembly. This ensures

satisfactory repairs and adherence to the specified

dimensions. Manufacturers have also carried out

numerous strength tests, and extended trials (crash

tests) have proved that part panel replacement is

just as effective as replacing complete new panels.

Provided repairs are expertly carried out, all repair

procedures using part panels will result in the same

standards of strength and operational safety being

maintained as for a new vehicle.

To carry out this type of repair (see Figures

14.101a–f), the initial procedure is to make certain

that the sections to be joined are from identical

models. Then determine the most suitable point

at which to make the joint: this will be influenced

by the length of the weld, the amount of distortion

likely to occur in making the weld, and the ease

with which it can be dressed up. Remove the bulk

of the unwanted section by cutting it away with a

power saw, leaving an allowance of about 20 mm

from the joint line, which can be trimmed to size

when the pieces of the panels are separated. Where

it is possible to fit the two sections on the vehicle,

it is considered good practice to trim only one edge

and to set the panels up with one section overlapping

the other, as this enables a check to be made

on the alignment of any surrounding or adjacent

panels such as bonnet edges and door edges.

A good butt joint is achieved by cutting through.

When the alignment is correct, the two sections are

tack welded along the length of the joint. The joint

is then hammered level and fully welded. After this

it is planished using normal techniques to achieve

a smooth, undetectable joint. If this is impossible

owing to inaccessibility, the weld should be hammered

in using a shrinking dolly and the weld area

filled.

Figure 14.100Welding-in new panel section

(Motor Insurance Repair Research Centre)

(a) (b)

(f)

(e)

Figure 14.101Replacement of part panels:

(a) clamping new panel section into place (b) cutting in

(e) dressing the welded joints (f) soldering the joint

and filing to a finish (Motor Insurance Repair

Research Centre)

Major accident damage 463

Vehicles that have undergone an extended corrosion

prevention treatment to prevent body perforation

by rust must be repaired using replacement

panels coated by the new (cathodic) priming

process. These panels are identified by corresponding

stickers. Therefore remove as little as possible

of the cathodic primer coating on replacement

panels during sanding or other abrading operations,

e.g. on spot weld flanges or in areas where welds

are to be made later. When repairs are being carried

out in the underbody area, the zone in question must

then be treated with underbody wax. The areas outside

the side members and the wheel houses must

also be treated with underbody protection material.

Repairing extensively

Damaged panels

Whenever possible it is best to repair severely

damaged panels while they are still attached to

the body shell. One advantage of leaving the panel

in position is that it remains rigid whilst being

processed. As already explained, it is difficult to

hold a panel firmly when it is not attached to the

body, and to beat a panel that moves with each

blow is most unsatisfactory. Second, the shape is

maintained while the panel is in position, and this

allows the edges of the panel to be lined up with

such parts as bonnets, doors and boot lids. In addition

the use of the body jack, while the panel is

fixed to the body, allows full use of the attachments

designed for roughing out such parts.

Having decided whether the panel will be

repaired on or off the job the actual repair can

then be roughed out, keeping in mind the fact that

the shape needs reforming with as little stretching of

the metal as possible. The original damaging force

could have stretched the panel and, while reshaping,

further stretching should be reduced to a minimum

by the use of such methods as pushing out the damage

with a body jack fitted with suitable rubber flex

head; or using a hardwood block between the body

jack and panel; or using hardwood blocks in conjunction

with the hammer to eliminate the metalto-

metal contact. Where necessary, anneal creased

sections with the oxy-acetylene welding torch prior

to removing them. As the roughing out proceeds,

weld any tears in the metal so as to gain rigid panel

as soon as possible. Very stretched sections can be

shrunk by the use of heat spots during the roughing

out. A boxwood mallet, in conjunction with a suitable

dolly block for the shape of the panel being

repaired, should not be used as an initial smoothing

or levelling step prior to the final planishing. The

actual smoothing with the planishing hammer and

dolly should never be started until the correct shape

is formed in the panel. At this stage the normal

processes of planishing, dressing up, filing and picking

up low spots should not be adopted until the job

is completed. Either because certain parts of the

repair are inaccessible or because of their overstretched

condition, it may be necessary to use solder

filling or plastic filler to achieve a smooth finish.

Repair methods using heat

Barrier material

This is a method of repair using a specially formulated

compound where heat would cause a problem

of distortion or overheating of adjacent materials

when welding.

The Cold Front heat sink chemical compound

was originally developed for the American space

programme. This heat barrier material, based on

a chemical formula of magnesium aluminium

silicate, prevents the conduction of heat through

metal, thus eliminating the risk of distortion to

panels, or damage to areas immediately adjacent

to any welding operation. When the material is

applied to a metal panel on a vehicle body undergoing

repair, it prevents the transfer of heat past

the Cold Front barrier, giving complete protection

to glass, rubber, plastic, paint and any material

likely to be damaged by close proximity to the

high temperatures which are generated during

the processes of welding, brazing or soldering.

The method of application is as follows:

1 Apply generously, as using too little can allow

heat damage. Apply to one side of the metal

in light gauge work (20 SWG) and both sides

of the metal when working with heavy gauge

(above 3 mm) for maximum protection.

2 When the mound of material begins to warm

up, it becomes saturated with heat. Once saturated,

it will allow heat to be conducted through

the metal. If there is still work to be carried

out, place more Cold Front material on top of

the existing mound to delay the conduction of

the heat.

464Repair of Vehicle Bodies

3 Always apply the material as close to the area

of repair as possible.

4 Damage can be caused by radiant heat as well

as conducted heat. The material acts as an

effective heat shield against radiant heat when

it is applied over the surface to be protected. Be

sure not to leave any cavities or depressions

when spreading.

5 It is safest to protect the repair area completely

around the heat zone. However, if protection is

only needed in one direction, the heat barrier

should be spread five to six times as wide as

the area to which the heat is being applied.

6 Metals have different conducting characteristics:

copper, brass and aluminium conduct

heat more rapidly than steel. Therefore the

better the metal is as a conductor, the more heat

barrier should be applied when working with

that metal.

Cold Front heat barrier is odourless, non-toxic and

harmless to skin. It will not stain surfaces, and any

residue can be washed off with cold water once the

repair is completed.

The ability of Cold Front to act as a total heat

barrier is demonstrated by holding a strip of 20

SWG metal in the bare hand after applying a line

of Cold Front halfway along the strip, then heating

the portion of the strip above the line to red heat.

The part of the strip being held in the hand remains

completely cold (Figure 14.102).

Door hanging

Door hanging requires particular care, as the fitting

of doors is one of the most essential features of

crash repair work. The most important aspect when

dealing with the hanging of doors is that a door

which is known to be the correct shape should

never be altered to fit a door opening that is out

of alignment. In addition, the resetting of door

hinges must not be used as a method of rehanging

doors without first checking for and correcting

any misalignment.

Hinges used on the modern vehicle can take a

good deal of force without altering their settings.

In cases where hinges have been subjected to collision

damage, the hinge transmits the damaging

force to the pillar or door frame, causing twisting

and misalignment. Sometimes hinges are so excessively

damaged that they need replacing, although

this is not the complete answer to correcting

misalignment troubles arising from such damage.

Where new hinges are necessary a close inspection

and comparison should be made with the identical

hinge mounting on the opposite side of the car,

and any misalignment of this mounting position

should be rectified before fitting the new hinge.

When it is considered that the hinge mounting

points are correct, the doors should be hung in

their respective positions and all screws or hinge

fixing bolts placed loosely to allow the door to

be realigned according to the car manufacturer’s

adjustments. The fixing bolts should be tightened

if possible while the door is in its closed position.

In most cases this is not possible, which means

that the doors have to be held open whilst at the

same time endeavouring to keep alignment correct

while the bolts are tightened. If the door aperture

is correct and the door is not twisted, with slight

adjustment to the hinge position the door can be

made to fit into its appropriate opening.

When the door will not fit into the body opening,

the hinges should be tightened in the main adjustment

position and the striker plate of the lock mechanism

should be removed from the locking pillar to

allow the door to swing freely. This gives a truer

indication of the swing of the door as the opening is

being corrected with the use of hydraulic equipment.

The door should then be closed as far as possible,

and the points stopping the door from entering

the door aperture should be noted. Correction in

Figure 14.102Application of Cold Front heat barrier

material (Gray–Campling Ltd )

Major accident damage 465

most cases can be made by diagonal pushing with

the body jack within the aperture. Measurements

should be taken both before and after applying the

pressure so that the effectiveness of the realignment

of the door opening can be assessed. This checking

and pushing must continue until the door is a good

fit inside the door aperture.

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