Hobbit Back Surgery

After discovering the degree that the tunnel was hacked, it became obvious that step one is shoring up this integral piece of the structure. Convertibles, lacking a roof to tie together and triangulate A, B, and C pillars, are not as rigid as fixed roof cars. The MG Midget was a unibody structure built from pressed sheet metal panels spot welded together. The primary longitudinal (front to back) strength came from the transmission tunnel and the sills/rockers. Compromise in these structures due to rust or modification greatly affects the integrity of body.

The tunnel shape would be difficult to do in one or two pieces so it was done piecemeal. The end result looks rather “tank-ish” but will work and disappear underneath carpet. I started the process by building a small frame that meets up with the transmission support under the car. This would give me a bridge to tie together the different sheet metal shapes. I then created the sides using cardboard as a template and cutting the sheet metal. A top was formed in a similar manner and lapped over the sides. I made the top flat and level rather than rounded as it was easier to form and will also make a nice base for a center console.

The metal was fastened using plug welds. Plug welding is a lap welding technique where a suitable size hole (1/4″ in my case) is cut in the top layer. The welder is then used to create a puddle of molten metal through the hole and onto the top layer. The finished weld looks rather like a button. Later welds in this project will get a bit better.

With the forward section welded up I moved onto piecing together the shapes that join to the rounded factory tunnel. These shapes were a bit trickier and required a bit more use of my cheap Harbor Freight sheet metal brake and lots more hammering. I marked the location of the shifter, removed the shifter, and closed up the tunnel. I then plunge cut the hole for the shifter using a grinder with cut-off wheel. The end result may look like Frankenstein’s monster but it should be stout!