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DIY Project 5

Method for repairing enlarged holes in sheetmetal

by Jean Caron, Vintage Roadster Restoration, Winnipeg, Manitoba

I will describe a method I use to fix enlarged holes on thin sheet metal, mostly 18 gauge, on Austin-Healeys. The most common locations for these are on the doors of the roadsters(100-6, 3000), where the side curtain socket is attached ,as well as the hole in the rear inner fenders used to secure the  rear seat backrest on all 4-seaters.

Through frequent use of the side curtains, the hole on the inside of the door tends to get enlarged quite a bit and, as a consequence of this, the bottom part of the side curtain socket becomes loose and difficult to secure in place. While a different problem occurs in the rear inner fenders, that of allowing water to seep in causing the wood pieces on the BJ8 model to rot, these problems should be taken care of during a restoration.

In order to repair these you will need the following tools: A round hand file and/or a drill with bits of suitable size;  sheet metal of appropriate thickness, 20, 18 or 16 gauge is what I mostly work with; thin cardboard (0.45” millboard); scissors; sandpaper or an air angle die grinder with 50 grit round 3M sanding discs; a metal shear; and Mig or Tig welder

For the purpose of this exercise I photographed the hole from the rear inner fender of a BJ8.

Illustration #1, seen from the inside of the car, shows the out of round, enlarged hole that, if left this way, will allow water thrown by the tires to seep in and damage the upholstery and the wood base of the rear backrest.


Step #1: - Sand the surrounding area to bare metal to facilitate welding later on. Then, enlarge the hole so it becomes completely round again. You can accomplish this with the round hand file or a drill bit of a size larger than the hole. When this is done, take a measurement of the new hole size and reproduce it on your sheet metal or, my preferred method is to place a piece of cardboard on one side of the hole, trace the size on the cardboard, cut the cardboard and then trace around it on the sheet metal.

Step #2:-Determine the gauge of the metal you are working with; this one here is 18 gauge. Next, cut your sheet metal to size, frequently checking how it fits into the hole you are repairing. Your new piece will fit into the hole for buttwelding. You do not want to overlap your weld here as you will want to keep the original dimensions. Before you obtain a proper fit, you will likely have to file or sand it a bit to get a perfect fit– see illustration #2. Now it’s time to weld it in place.


Step #3:- is to weld the sheet metal in place and then clean your weld. For that purpose I use an air angle die grinder with the 50 grit 3M sanding disc until I get a smooth surface. Illustration #3 shows the sheet metal just welded in place.


Illustration #4 shows the surface after the sanding is completed.


All there is left to do now is to locate the centre spot of your newly repaired surface and drill the new hole to the size appropriate to the item going through it, in this case a 3/8” hole for the flat head, countersunk machined screw used to secure the side support for the folding backrest.

Illustration #5 shows the finished work.

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