An Open and Closed Case

Welding Up Unwanted Holes

By Ron Ceridono   –   Photography by THE AUTHOR & Tim Foss

Regardless of whether a classic truck is being modified or restored, chances are that during the bodywork phase of the project there will be holes in the sheetmetal that will have to be filled. As a general rule (keeping in mind there are extenuating circumstances), small holes less than a 1/4 inch in diameter can be filled by welding only; bigger than a 1/4 inch a copper backup plate should be used. Holes 3/8 inch and larger should have plugs welded in place.

- Advertisement -
CTP JUNE 2023 Gas Filler Hole Filling 01
The small 5/16-inch hole is typical of the holes in his pickup that will be plugged. The first step was to clean the surface with an abrasive disc.

Now the extenuating circumstances. First is the type of welder being used. The key to success is to use as little heat as possible, so despite what you may see in some of the older magazines, oxyacetylene welding should normally not be considered. That leaves MIG and TIG welding, which both work well, but most hobbyists will rely on a MIG welder because wire welders are most commonly found in home shops. Another factor is ability; if you’re an experienced welder, filling holes shouldn’t be too difficult. If you’re new to welding, drill holes in some scrap sheet and practice filling them. You’ll soon discover that controlling the amount of heat that is put into the metal is one of the keys to success. Too much heat will cause the metal to warp; that has to be avoided because it can be very difficult to repair, particularly for a novice.

CTP JUNE 2023 Gas Filler Hole Filling 02
An easy way to close holes is to use a copper backup plate held tightly against the backside of the metal. The plates without the handle have magnets to hold them in place.

Another consideration when filling holes is not to stack up a huge bead that requires a great deal of grinding. Keep in mind grinding can also create heat that may cause the area to distort. Another common mistake is grinding too much, making the area surrounding the weld thinner than it should be. The idea is to level the weld bead to match the surrounding metal and no more.

CTP JUNE 2023 Gas Filler Hole Filling 03
Copper backup plates do two things: They act as a heat sink to help prevent warpage from welding and they make the hole easier to fill as the weld wire won’t stick to the copper.

To demonstrate two different techniques we watched as Paul Wilson filled a hole in sheetmetal with a copper backup plate and his Miller MIG welder. Given the variations in welders and individual preference it’s impossible to recommend machine settings. The best advice we can offer is again to practice on scrap material that matches the thickness of the vehicle you’ll be working on.

- Advertisement -
CTP JUNE 2023 Gas Filler Hole Filling 04
The completed weld is virtually flat and will require little grinding to make it flush with the surrounding area.

Filling small holes is usually done by making small tack-like welds around the edge of the hole, working your way to the center (it may help to slightly countersink the hole). Work slowly and try to keep the weld as flat as possible. If there is access to the backside of the hole being filled, copper backup plates, like those shown here, are particularly helpful.

CTP JUNE 2023 Gas Filler Hole Filling 05
To dress the weld a 60-grit “flapper” disc was used on a 4-inch electric grinder. The trick is to go slow and not apply excessive pressure, which can create heat and warp the metal—the very thing you’re trying to avoid.

For larger holes, filler plates will be required. Tim Foss followed Kev Elliott, of Kev’s Rod & Custom, as he plugged the gas filler opening in a ’72 Ford pickup with a gas filler delete plate from LS Fabrication. Made from laser-cut, 16-gauge steel, the filler plate is contoured to match the contours of the cab.

CTP JUNE 2023 Gas Filler Hole Filling 06
After careful grinding, the location of the hole is practically undetectable.

After preparing the area to be welded, Elliott went about tack welding the filler plate in place with his TIG welder. A few deft taps with a body hammer had the filler plate fitting perfectly—after that the welding was completed and then ground smooth.

CTP JUNE 2023 Gas Filler Hole Filling 07
We caught master metalman Kev Elliott plugging the gas filler hole in an F-100. The first step was to remove the paint and taper the edge of the hole for a better weld.

Remember when filling multiple holes move around to keep from concentrating too much heat in one area, try to keep the weld bead height to a minimum and use restraint when grinding. Filling holes in your hauler can be intimidating at first, but with patience and practice it is a skill that you can master.

- Advertisement -
CTP JUNE 2023 Gas Filler Hole Filling 08
While tack welding, Elliott used magnets to hold the LS Fabrication filler plate in place.
CTP JUNE 2023 Gas Filler Hole Filling 09
Elliott used a TIG welder to make the initial tacks, then the magnets were removed.
CTP JUNE 2023 Gas Filler Hole Filling 10
Skipping around the circumference of the tack welds were made in-between the tack welds.
CTP JUNE 2023 Gas Filler Hole Filling 11
When filling holes in a surface with compound curves, such as this one, a hammer and dolly or two may be required. We’re willing to bet this is Elliott’s favorite hammer.
CTP JUNE 2023 Gas Filler Hole Filling 12
By holding the dolly against the inside of the body, the filler was “massaged” to fit perfectly.
CTP JUNE 2023 Gas Filler Hole Filling 13
Satisfied with the fit, the filler plate was welded completely and then the edges were ground smooth.
CTP JUNE 2023 Gas Filler Hole Filling 14
When Elliott was finished, the contour of the filler plate matched the surrounding area perfectly. After primer and paint, the modification will be undetectable.

Things You Should Have in Your Toolbox

Here are three examples of sheetmetal tools you should have in your garage. We dug these out of our toolbox and grabbed some random scrap metal pieces to show how they are used.

CTP JUNE 2023 Gas Filler Hole Filling 15
For those occasions when sheetmetal panels have to be perfectly aligned, such as installing floorpans, quarter-panels, and the like, Summit Racing offers these butt-weld clamps (PN SUM-9785235).
CTP JUNE 2023 Gas Filler Hole Filling 16
When installed, these clamps maintain a 0.40-inch gap between panels, perfect for edge-to-edge welding. The number of clamps needed varies. For large panels, we’ve found over 6 inches works well.
CTP JUNE 2023 Gas Filler Hole Filling 17
Obviously access to the back of the pieces being welded is necessary to install and remove the clamps. In tight spaces we’ve used a magnet to grab the crossbar when the wing nut was loosened.
CTP JUNE 2023 Gas Filler Hole Filling 18
In situations where panels overlap, Cleco pins and clamps are indispensable. Summit Racing offers the pliers with 10 1/8- and 15 3/16-inch pins under PN SUM-G1850. Clamps are available separately.
CTP JUNE 2023 Gas Filler Hole Filling 19
After drilling the appropriate-size hole in the panels to be joined, the pliers are used to extend the tip of the pin. When the Cleco is released, the spring-loaded tip retracts and expands, locking the two pieces of metal together.
CTP JUNE 2023 Gas Filler Hole Filling 20
Again, the number of Clecos necessary varies on how well the two pieces fit together. Once the Clecos are removed the small holes are easily welded closed.
CTP JUNE 2023 Gas Filler Hole Filling 21
In situations where the edges of two pieces of metal are clamped together, these Mittler Bros. Cleco Side Grip Clamps are available from Summit under PN MB-TP125SG. They work with the same pliers used to install the pin clamps.

SOURCES
Eastwood
(800) 343-9353
eastwood.com

Kev’s Rod & Custom
(714) 686-8982
facebook.com/kevsrodandcustom

LS Fabrication
(780) 678-946
ls-fab.com

Miller Electric
Manufacturing Company
millerwelds.com

Summit Racing Equipment
(800) 230-3030
summitracing.com

- Advertisement -

Related Articles

Search Our Site

More Chevy Performance

How to Avoid Fuel Starvation Problems When Building High Horsepower LT1 Engines

By Jeff Huneycutt   -   Photography by the Author Critics have...

Fresh Fuel Delivery for a Crusty 1977 Nova

By Tommy Lee Byrd   -   Photography by the Author If...

Double Dose of 1969 COPO Camaros With Different Personalities

By Scotty Lachenauer   -   Photography by the Author We’ve all...

Suspension Upgrade: Aldan’s Coilover Kits for C2 and C3 Corvettes and Full-Size Chevys

By Ron Ceridono   -   Photography by the Author Hot rodders...

Totally Custom Pro Touring-Style 1967 Chevy Chevelle

By Nick Licata   -   Photography by John Jackson Growing up...

Firing Up — All Chevy Celebrates its Third Anniversary

With the Jan. ’24 issue of All Chevy Performance...
More Chevy Performance

Firing Up – Decisions, Decisions

By Nick Licata Being an automotive magazine editor, I get...

2023 MUSCLE CAR AND CORVETTE NATIONALS

Another Year of Fresh GM Muscle at MCACN By John...

Longevity

Tom Schauppner’s ’56 Chevy Bel Air By Nick Licata   -  ...

Chevy Concepts – 1970 Camaro

Artwork by Tavis Highlander Instagram @tavishighlander TavisHighlander.com Vehicle Builder: Vintage Fabrication, Independence,...

Back to Basics

Keeping Drum Brakes in Service is Simple and Affordable By...

Zora Inspired

Mike Schultz’s 1965 Corvette Grand Sport Tribute By Nick Licata  ...