A weak point in the Tiger's super-structure is the front mount for the rear spring. In restoring my Tiger I found that both sides needed attention. While I was at it, I designed a metal patch that not only strengthens the spring mount but also reinforces the frame at this critical point.
The patch can be cut from any piece
of suitable sheet metal. I used a rather heavy 12 or 14 gauge. The only critical
dimensions are the size and position of the mounting hole, which must be determined
after the patch is cut and fitted to the frame. The patch should look like the
following diagram:
The pattern for the patch will work for either side of the car - just make the bends in the opposite way so the two plates are mirror images of each other. The patch somewhat resembles a horse, with three bends along the dashed lines. The 90-degree bend roughly corresponds to his stomach and allows the patch to be attached to the two sides of the X-frame. Shape the bend at the "neck" to fit the angled X-member and the straight rear frame member. Bend the "nose" 90 degrees to allow the rear portion of the pattern to fit the front portion of the rear sub-frame. In bending, watch the alignment of the mounting bolthole. Once you have actually cut out the patches, it is fairly obvious how they fit.
Patches should be installed on the inside of the frame where the X-member begins to straighten out. Be sure to check the other welds and repair any cracks before applying the patches. Remove the spring from the front mount so the heat doesn't damage the rubber bushing, then insert a spare bolt through the patch to keep everything in alignment. Also, test fit the plate and spring to be sure it all fits in place easily and that the spring bolt will engage fully. Shape the patch to a tight fit against the frame member using a ball-peen hammer, then weld. One way to be sure to keep weld splatter out of the threads in the mount is to insert a carbon rod (such as the kind found in the centre of a D-size flashlight battery) into the hole before welding starts. Be sure to clean the rod thoroughly before use.
To add more strength to the patch, make the holes slightly larger than needed, then weld a bead around the hole as well as along the frame members.