180 Section 2 Nonstructural Repairs
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 a red color. The heated
portion should be no larger than a dime. Put the flat
dolly on the back side of the panel. Use light off-dolly
taps around the heated area. Continue tapping until the
heated area has cooled enough to touch. Next shrink
the highest remaining area. This will gradually lower the
stretched high area.
An oxyacetylene torch (with a small tip) or a butane
micro-torch can also be used to remove hail dents from
a low or medium crown panel. The flame should barely
touch the deepest part of the dent. The heated metal
expands but is restricted by the surrounding cold metal,
so it moves up. This upward movement may be enough
to eliminate the dent. If not, repeat the process. See
Figure 8-35.
Another shrinking technique does not use heat.
Instead, the stretched metal’s surface area is reduced
by kinking. Kinking involves the use of a shrinking
hammer (serrated-faced hammer) or a sharp pick
hammer to reduce the surface area by gathering the
metal together. To use a shrinking hammer, push up on
the stretched low spot with a flat dolly. Tap the bulge
with the shrinking hammer. Hammer taps should be off
dolly but close to the dolly’s edge. You will notice that
the serrations on the hammer face produce small kinks
on the metal’s surface. Continue tapping until the metal
is level.
To use a pick hammer for shrinking, place a flat dolly
on top of the stretched area as shown in Figure 8-36.
Tap up on the stretched metal with the pick hammer. The
dolly prevents the metal from moving too far. The pick
hammer raises and shrinks the metal at the same time.
Beginners often encounter problems when repairing
a low-crown panel, such as a hood. Consider the front of
a hood that is damaged, bumped, and filled. The techni-
cian may find a high area around the sanded filler. As
the next step, the high area is tapped down; then more
filler is applied and sanded. Another high area is discov-
ered adjacent to the filler’s edge. The tapping, filling, and
sanding process is repeated. This is called chasing the
dent. Chasing the dent occurs because the low-crown
metal is floppy and is easily pushed in. The pressure
from sanding causes the floppy metal under the filler to
be pushed down.
To prevent chasing the dent, tighten any floppy
metal around the area to be filled by making a shrink
fence. A shrink fence is simply a line of small kinks
made with a sharp pick hammer. See Figure 8-37. The
shrink fence tightens the floppy metal in the low-crown
area, allowing the filler to be sanded level.
Butane torch
Figure 8-35. A butane-powered torch can be used to
raise small hail dents.
Stretched metal
Dolly
Figure 8-36. Kinking with a sharp pick hammer will
reduce surface area in stretched metal.
Figure 8-37. A pick hammer is used to make a shrink
fence in a panel.