Before repairing a
rusted area on a car, a "battle plan" must be carefully worked out. If
there is any body filler or damage nearby, consider replacing more than
just the rusted area. If adjoining panels are also rusted, a logical
sequence of operations must be planned. Above all, have your Moss
repair panels in hand before cutting rusted/damaged areas out of your
car. This not only makes planning the job easier, but it lets you see
exactly how the repair panel will fit. It's also a good way to prevent
cutting out an area larger than the repair panel - a potentially costly
mistake. Careful measurements and marking are essential.
Plan with care. Star
from the inside out. Floors and sills (always before removing the body
from the frame if the car has a separate frame) are followed by inner
fender and door pillars, after which come rocker panels and then fender
patches. This is, of course, a very general outline.
Equipment needed to
produce professional quality repairs is generally beyond the tool
inventory of the average enthusiast's garage, but it is often cheaper
to purchase needed tools and equipment than to take the car to a body
shop, especially if only "skin" repairs are required. The most
expensive item required for this is most likely a M.I.G. welder or
oxy-acetelene torch set-up to do the actual welding. (If only non-stressed areas are to be repaired, pop-riveting is usually
adequate.) A few years back, an "inexpensive" M.I.G. welder cost just
under $1,000.00. Recently there have been "tabletop" models available
starting under $300.00, which puts these invaluable devices within the
reach of many.
For cutting the rust out
of your car, I have found a hand-held 4" grinder with a cutoff disc to
be quick, clean, and accurate. These have the added advantages of
producing virtually no distortion in the metal, and can be used with
grinding discs for grinding welds. Chisels, hand shears, and cutting
torches should not be used on most external panels, as they produce too
much distortion in the surrounding metal. Cutting torches are great for
rough or preliminary work. Nibblers maybe used, but are generally slow
and leave a slightly ragged edge. They are good for cutting small
radius curves, however.
Spot welded panels, such
as rocker panels, can usually be removed by carefully drilling the spot
welds with a drill of slightly larger diameter then the welds. If the
welds are drilled out through the entire assembly, the new panel may be
plug welded from the "back" of the holes. If done carefully, appearance
of the original spot welds can be approximated. In any case, once the
spot welds are drilled, the old panel may be separated from the piece
it was welded to with a thin sharp chisel and vice-grips. Rocker panels
are easy to remove if the main part is cut away from the welded
flanges, and the flanges removed separately.
Repair panels may be
mated to the cuts made in the car by overlapping or with butt-joints.
Overlaps are easily made, and may be welded or pop-riveted, but they
leave a grossly unfair surface unless the edges of the "hole" are
joggled, so that the surface of the patch and any rivet beads are
slightly below the surface of the main panel. The time and effort to do
this properly makes this method more difficult than butt welding. Butt
welding is the joining of two pieces by their edges, and demands
careful matching of the edges.
Which ever method is
used depends on equipment available and what sort of panel is being
installed- floorboards and trunk pans can be installed with lapped
edges, while exterior "patch panels" should be butt joined if a minimum
of body filler and finishing is to be used.
Plan where to run the
joint. Fox example, some MGB lower fender repair panels run just above
the waist line (where the chrome trim goes). It is much easier for many
reasons to trim the repair panel so the weld is along the bottom of the
original joint line, and will be hidden by the chrome trim.
Plan for drainage -
there was a reason the car rusted where it did. Figure out why, and add
inconspicuous improvements such as extra drain holes where required.
To install a panel, mark
on the body of the car approximately where you think the edge of the
repair panel will be. Remove all of the original pieces to be replaced
except for an inch or so along where the main joint or weld will be. It
should then be possible to scribe an accurate line on the body for the
final cut where the two panels will join. Cut this carefully with as
little distortion and with as smooth an edge as possible.
Hold the repair panel in
place, and note any areas which need attention. These could be unfair
mating flanges, ragged surfaces (remnants of old welds, barbs left from
rough chisel work, or slag from cutting with a torch), or poorly mating
edges. Look for imperfections in the repair panel itself. Trim, grind,
hammer (gently) or do whatever is required for a perfect fit all over.
With the repair panel
held or lightly clamped in place, place a small "tack" weld at the
center of the major joint. In the case of a lower fender repair panel,
especially when the weld will not be covered by trim and the joint is
straight, allow the contraction of this "tack" to pull the bottom of
the panel away from the car slightly - when later "tacks" are made, and
the bottom of the panel pushed into place, the joint will (usually) be
slightly below the "correct" surface. The idea is to have the finished
(ground-off) weld slightly "low", so a light coat of body putty or lead
is all that is needed to bring the repaired area to smooth perfection.
With the first tack in
place, wiggle the panel around a bit for perfect alignment, and place
more tacks at 2-3 inch intervals from the center outwards in both
directions, one on one side of center, the next on the other side, and
so on.
By leaving a small gap
between the two pieces to be butt-welded (about 1/32" is fine), a small
thin screwdriver or other object may be used as a lever to pry the two
pieces as required to perfectly align the two surfaces at each tacks.
With the "cosmetic"
joint(s) well tacked, weld the flanges and other edges of the panel,
being careful not to allow enough heat to build up to cause any
distortion. The best way to do this is by "skip-welding", in which
short welds are made at long intervals around the work until it is
finished. Now go back and put a tack weld between each of the previous
ones on the "cosmetic" or "exposed" joint, aligning the surfaces as
before. Do it again - a tack between the ones just made and the
original ones. If the resulting gaps are more than about 1/2" long, do
it again. With a hand grinder, carefully grind off the tops of all
these little tacks welds. After aligning the surfaces as before, use
the skip-welding procedure mentioned earlier, to carefully weld in the
gaps, again being careful not to cause adverse heat distortion.
Grind off the excess
weld carefully, without hitting the body panels. If you find the weld
to be in a slight depression, congratulations! If the ground weld is
still slightly raised, do not try to grind it and the edges of the now
joined panels flat - you will make the metal too thin, and cause the
weld to crack. Careful hammer work or heat shrinking is the only cure -
consult an experienced body man and/or a good book on bodywork.
Common questions about
repair panels are: (1) Why not braze them? (2) Why not sell galvanized
panels? and (3) Why aren't all the repair panels supplied in primer?
Brazing can be used, but causes paint adhesion problems unless proper
preparation and primers are used. Galvanized panels should not be used,
as the fumes from welding these are highly toxic. Furthermore, as the
zinc is burned off at the welds, protection is lost where it is most
needed. All body panels should be stripped to the bare metal before
finishing, and properly prepared for paint. It is easier to work with
oil-covered or even slightly rusty panel than one already covered with
primer that must be removed, as it must be thoroughly cleaned anyway.
Eric Wilhelm
Moss Staff