This month we're going to focus on the creation of the most unique part of Alpine's BMW X5--the door system. We knew this was going to be the hardest part of the installation process, so it was one of the first things we did on the vehicle. The basic concept goes like this: We weld the doors together; then we build a sliding mechanism on each one of them so that they slide straight out the side of the car. Finally, we attach our seats to these sliding tracks so that they too slide with the doors.
In order to make the doors as light as possible, all of the interior structure, including the windows, door locks and door trim, had to be removed. The interior metal in each door was also cut away with an airsaw, since we would be adding our own structural support later. The edges of both doors were ground down to bare metal, then a 1/8" steel rod was placed in the gap between the front and rear doors. The doors were carefully MIG welded together while they were still on the car to make sure the alignment was correct. After removing the hinges from the rear door, the whole door could now be opened, making the world's biggest coupe! This step was only temporary, as we left the front door's hinges in place until we could attach the doors to the sliding mechanism.
A 2" x 4" steel brace was welded below the doors for support, then it was time to cut out the X5's B-pillar. The easiest way to do this is with a Sawzall, and we use a blade called "The Torch" that definitely lives up to its reputation. This 10" long blade sliced through the pillars like they were made of paper, and the B-pillars were removed.
The window pillar in the now one-piece doors also had to be removed, but not before some temporary structural bracing was welded in place to keep things strong. This pillar was also cut with the Sawzall in short order. Steel tubing was welded on the top and bottom edges of the window area to make the joint between the doors even stronger. With a door that's over 6' long, more structural bracing is always good.
The hardest part of the whole process was re-building the area where the pillars had been cut out. We knew that we had to eventually use one long rubber door seal to seal up the car, but to do this we needed to fabricate some sheet metal panels that continued the metal edge around the top and bottom of the door jambs. These pieces were built using a small metal brake to mimic the shape of the door jam; then they were welded in place. This was done at the top and bottom of each side to complete the project.
That's it for this month. Send any questions to
sbrown@alpine-usa.com and check out
SteveBrownUniversity.com.
We used a Sawzall with a long metal blade to cut the B-pillars out of the body. | 
Here's a good shot of the inside of the welded doors before any cross-bracing was added. | 
With the main pillars out of the way, the remaining material is trimmed off. |
The pillar between the doors is the next to be cut out, also done with a Sawzall. | 
With the B-pillar gone, the large window opening can now be seen. This will allow an easy view into the car even when it is closed. | 
One-half-inch hollow steel tubing was welded to the exterior seams of the window openings, adding stiffness to the structure. |
Sheet metal panels had to be made to continue the door jam line where the B-pillars were removed, so we made them on a bending brake and welded them in place. | 
The bottom door jam area also received sheet metal to continue the lines, hiding the area where the B-pillar was removed | |