188 Section 2 Nonstructural Repairs
Copyright Goodheart-Willcox Co., Inc.
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 9-35.
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 9-36. 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 technician 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 discovered 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 a line of small kinks made
with a sharp pick hammer. See Figure 9-37. The shrink
fence tightens the floppy metal in the low-crown area,
allowing the filler to be sanded level.
Technicians sometimes oversand the filler. The
excessive sanding leads to undercutting, a condition
in which filler is sanded below the level of the adjacent
metal. When comparing the filler height to the height
of the adjacent metal, the technician misdiagnoses
the undercutting problem and taps down the adjacent
metal rather than refilling the low area. Undercutting
should not be confused with chasing the dent.
Goodheart-Willcox Publisher
Figure 9-36. Kinking with a sharp pick hammer will
reduce surface area in stretched metal.
Goodheart-Willcox Publisher
Figure 9-35. A butane-powered torch can be used to
raise small hail dents.
Goodheart-Willcox Publisher
Figure 9-37. A pick hammer is used to make a shrink
fence in a panel.
Butane torch
Stretched metal
Dolly