187 Chapter 9 Nonstructural Panel Repair
Copyright Goodheart-Willcox Co., Inc.
low-crown panels. Uncontrolled use of heat on a low-
crown panel will cause warp damage. Warp damage
is a group of high and low areas in a panel. Warp
damage is difficult to remove, if not impossible. Always
use the minimum amount of heat required when
shrinking.
One heat shrinking technique commonly used
to eliminate false stretch involves the use of a draw
pin welder and a shrinking tip. If a shrinking tip is not
available, use the draw pin welder without a pin. If
hammering on a nearby body line does not cure false
stretch, heating with the draw pin welder will remove it.
Locate the false stretch and pop it in. Grind or sand off
the paint from the false stretch area.
Push the shrinking tip onto the false stretch and
pull the trigger on the draw pin welder. Keep the welder
on for about one second. The false stretch should
remain down and not pop up. If it does pop up, repeat
the procedure. If the false stretch is so big that pushing
in on one area causes another area to pop up, try
shrinking the metal between the two areas. Usually, a
false stretch area that has been shrunk must be filled.
You can also shrink a high spot using a draw pin
welder and the draw pin welder tip (or a shrinking tip).
Place the tip on the high spot and press the trigger in
for one second. Then tap the heated area twice with
a flat-faced dinging hammer and immediately cool the
heated area with a wet rag. This method works well on
high spots that result from pulling draw pins above the
surrounding metal.
Another shrinking method involves the use of an
oxyacetylene torch or a butane-fueled micro torch to
remove a low spot. This procedure will require heating,
putting down the torch, and using the hammer and
dolly, all in a brief period of time. Therefore, a dinging
hammer, a flat dolly, and a wet rag should be nearby.
Be sure to locate a safe place for the hot torch before
you start. The stretched area should be stripped to
bare metal first. When using an oxyacetylene torch,
use a small tip, such as a #1 tip. Light the torch and
adjust it to a neutral flame. The hot spot of the flame
should be concentrated on the deepest part of the
stretch. The heated area must be no bigger than a
dime. See Figure 9-34. As steel heats up, its color
changes from silver to blue and then to red. The
heating will cause the grains to thicken, reducing
the surface area. With less surface area, the metal
contracts, raising the low spot. Immediately after the
steel changes color from blue to red, turn off the torch
and set it down. Tap around the heated area with the
dinging hammer. If the back side of the panel is acces-
sible, the dolly can be used to support the panel. Use
light hammer-off-dolly blows to level the area. Once the
color has disappeared, the wet rag can be used to cool
the area. Using the wet rag to cool the area while the
metal is too hot with color can make the metal brittle.
The area that has been shrunk will be harder than the
surrounding metal. If many shrinks are needed, shrink
the most stretched area first, but do not quench it (cool
it with the wet rag). Shrinking with heat will burn rust-
proofing from the back side of the panel. Be sure to
replace the rustproofing after heat shrinking.
As damaged metal is straightened, a stretched
area, originally a low area, may become raised. The
area is still stretched, but it is now high instead of low.
A torch can also be used to shrink a stretched high
spot. Locate the highest part of the stretch. This area
will have the most stretch. Shrink this area first. Heat
up the area with the most stretch until it just reaches
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Figure 9-33. The first step in this repair is to align the
door edge. Tapping on the ridge with a dolly will move
the edge.
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Figure 9-34. A torch is used to heat a small circle on a
stretched panel. Notice the color of the heated metal.
Oxyacetylene torch
Dolly