MG Midget

Passenger Inner and Outer Sills

With the floor pan in place, it is time to weld up the inner and outer sills. The sills in this car serve as part of the three main members of longitudinal rigidity for the roadster. Driver’s sill, tunnel in the middle, and passenger sill. The inner sill is a flat piece of sheet metal with two large holes where the car’s jack points protrude. The inner sill is fastened to the outer floor flange, footwell end, chassis leg, and outer bulkhead skin with plug welds. To prepare it for welding, it is clamped into place. I then use some contrasting paint (primer gray) to dust along where it meets the floor flange. This helps me to determine where to drill the holes (for the plug welds) in the inner sill to meet the floor flange. Prepping the panel consists of punching or drilling 1/4″ holes in the sheet metal. For each hole there will be a plug weld. Additionally, for the base surface of each weld, I grind off the paint and apply weld-through primer.

Welding the inner sill is a pretty straightforward process since most surfaces can be clamped tight with deep jaw pliers. For this step, I also cut away the rotted A post and installed new outer footwell sheet metal. Since the A post was compromised and needed to be cut away, the outer footwell sheet metal helps to ensure that the sill and floor are in the right placement for later cosmetic pieces such as the outer sill, fender, and A post.

With the inner sill in place, I was able to move onto the outer sill or rocker panel. While the inner sill’s alignment is important, it effectively just seals up the “tub”. The outer sill is seen when the car is finished and becomes the reference for setting the panel gaps for the bottom of the door and the front fender. Prior to welding it into place, it is best to temporarily install the door and set in place the front fender. My problem was that I had fully cut away the A post so I had nothing to hold the door hinges. I clamped and used sheet metal screws to fasten the inner A post to the footwell sheet metal. This allowed me to check for basic alignment and be largely ready for final install of the inner A post. When I was reasonably satisfied, I removed the door, A post, and fender and fully welded in the panel.

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