Beogram 4004 (5526): Repair of a Cracked Plexiglass Hood

The Beogram 4004 (5526) that I am restoring right now came with a hood with a crack in the hinge region. This shows the crack after moving the metal hinge part:

Many Beogram hoods suffer this fate since the holes for the mounting bolts of the hood hinge represent a mechanically weak spot. Combined with the brittle nature of plexiglass and the torque acting on the hinge region this can lead to stress fractures. I recently developed a method to repair such cracks when I needed to save a rare Beogram 4000 hood. For this project I developed laser cut patches that are thin enough to still permit mounting the hinge after the repair. Before applying the patches, however, the first step is to glue the cracked parts back together to maximize strength of the repaired area. This can be done by simply pressing them together and infusing a bit of Weld-On #4 acrylic solvent into the crack. Capillary forces draw the water thin liquid into the crack where the abutting sides are dissolved in the interface region. Evaporation finally cures the dissolved regions into one piece of plastic:

After 5 min of holding the parts together one can let go and add the patches to further stabilize the part:

If the hood area is smooth enough one can also use #4 for gluing the patch on. If the area is rough, higher viscosity #16 is better for the task. Here #4 did the trick. I also applied a patch to the outside and moved on to the other side of the hood where cracks are already developing:

On this side I only applied a patch on the inside, since the crack was not fully developed yet:

After letting the acrylic harden for 24 hrs, I bolted the hood hinge back in and then glued the side parts of the aluminum strip to the plexiglass with ultra thin double sided tape. This shows the side that had the fully developed crack:

The outside patch made the hood a bit wider, i.e. the aluminum strip is slightly offset from the hood surface....Unfortunately, the aluminum strip already had developed a small crack where it is bent, but I was able to catch it in an early stage and it is hardly visible. At least this hood can be used again!