The first step after receiving the cage was to unpack and assemble outside the car to check everything was pressent and correct. As you can see from the pic's below the cage ordered was a standard 6 point item, we will be using a multi-point item for this shell but all we needed to purchase was the standard cage and the rest we will fabricate ourselves. The standard cage shown below is perfectly adequate for occupant protection however it can be greatly improved upon to provided much more structrual strength for the shell. There are multi-point weld in cages available from the main manufacturers but the prices for these are expensive to put it politely, we've also found from fitting cages to various cars that the tollerences to which these cages are made can sometimes be a little shabby, this coupled with the fact that most older cars will have slightly different dimensions to each other due to years of use, make it a lot easier to tailor fit a custom cage for each one.
The first pic above shows the cage as it arrived, a 6 legged cage which bolts to the floorpan at the bottom of the A and B pillars and also two legs extending rearward which bolt to the innar wheel arches. The first task was to remove the rear facing legs which are outlined in the second pic in red and replace them with legs which would pick up both the axle mounting points on the floor and the rear turrets. The reason for this is it greatly strengthens the shell as it allows the pounding the rear shocks and springs place on the rear turrets to be passed on to the cage and dissapate it much more effectively and evenly around the car rather than continously in the one place.
As you can see from the above pic the cage now extends to the rear turrets at point A rather than bolting to the wheel arch liner. The cage also picks up the axle mounting points at point B which releaves the local stress on the shell from the axle trying to pull the mounting everywhich way during hard cornering.
The area where the 4 front mounted legs were to bolt to the floor pan would also have to take some beefing up to prevent the cage seperating from or through the floor in the event of a major impact. The cage we purchased came with some steel brackets which needed some slight tailoring to be perfectly suited. With this done all that remained was to prepare the area for them to be welded in.
With all these plates welded in and one final bar added to the rear section of the cage to act as a rear strut brace we could now start adding the front pick up legs. If you have ever seen a muti-point roll cage fitted to another car you might have noticed some bars running forward through the engine bulkhead out to the top of the front turrets. The reason for fitting these is they greatly help the front chassis legs and turrets absorb the pounding they receive in competition use. If you look at the first pic below you'll see a rather crude drawing of the front of the BM
The red squares indicate where we have seem welded the chassis leg to the main shell and the turret to both the chassis leg and innar wing. Now, let us consider life as a chassis leg for a minute, fitted to a car which is to be driven shall we say enthusiastically. It will spend most of its life being pounded upwards in the direction of arrow A as the wheel bounces over humps and bumps and passes the shock loading up through the springs, on to the turret, which will in turn try to pull the leg upwards. Then as the saying goes for every up theres a down, and acting downwards on these chassis legs (arrow B) is the weight of an engine and most of the gearbox not to mention most of the weight of the front of the car. It doesn't take much imagination to see without any additional strengthening, that, as shown in the pic below, chassis leg failure could be the result in the worst case senario!
Although this would be at the extreme end of the scale, its given as an example to show some of the stresses on the chassis legs. To help strengthen the chassis legs we've already beefed up the welds throughout as shown earlier, but now were going to go a little further as shown in the pic below.
In the above pic the bars shown in red are the standard cage as fitted to the car. The 2 bars in purple are what we intend to add in. The idea being that when the shock loading is now passed up from the wheels through the springs into the turrets and in the opposite direction downwards, the forces involved now can be disipated much more effectively through both the leg and the new support bars, resulting in a much easier life for the chassis leg. As with most things in life though talking about it is a lot easier than doing it and the cutting of the bulkhead and joining of the bars is quite tricky. However a lot patience and long hours got the job neatly done.
The last step needed to complete the cage installation was to "tag" various bars to the surrounding bodywork, we have chosen 5 common places in our cage to tag to the shell. The tagging involves welding a small bit of flat steel between the cage bar and a close by point of the shell, again its for strengthening purposes and helps tighten up the overall car in places that are usually distant from the main bolt and weld in points of the cage. The pic below shows 3 of these tags outlined by the red boxes and out of frame are another 2 on the "A" pillars or windscreen pillars.
With the cage and shell reaching completion it's time to move on to the bodywork and paint, please click on the link below to follow the progress.