Piecing together the Installation Kit
The installation kit (part no. 82 11 9 402 709) contains everything you need to mount the front and rear CSi spoilers to all years of the 840 and 850. Some have reported that the kit is no longer available from BMW. Piecing the kit together by ordering parts separately is an alternative (See Part Numbers). Note that care should be exercised since the kit includes the special cooling duct (See above), a handful of other small plastic air ducting parts (to date, no has been able to source these separately by part number), and all the pieces necessary to mount the front and rear spoilers. The kit also includes the lower front spoiler lip, rear spoiler mount/reinforcement, various rivets, clips, etc., and the everimportant installation instructions. The instructions are also included in the kit. As an alternative, see below for a summary of the installation procedure.
Painting instructions contained in the kit specify a paint ratio of 30% softface additive and a maximum stove-enameling temperature 40 degrees C. Sikkens is the OEM paint supplier to BMW.
If you are lucky enough to find a kit, note that since the it contains the rear CSi diffuser reinforcement piece (51-12-2-252-015) you don't need to order it separately or you'll end up with an extra one (as I did).
If you're considering piecing your own kit together or skipping it because you are installing only the front or rear spoilers, consider BMW's clear warning: "To guarantee safe dynamic handling characteristics, only ever fit the complete package consisting of both the front and rear aprons. BMW AG will accept no liability for any damage caused through this instruction not being followed."
M-Technic (CSi) Installation Instructions
The following is an excerpt from Steve Castle's detailed e31 Email List post detailing the removal and installation process for CSi body parts. The first section covers reinstalling
the rear bumper apron, CSi air diffuser and rear wheel well trim. The second session covers re-assembly of the entire nose of the car, including the entire intake system in front of the DK motors, as well has the headlight assemblies.
Rear apron assembly
R&R of the rear apron and bumper (as a single assembly) is surprisingly simple. Start by removing the wheel well trim on each side after removing the rear wheels. Next remove two screws on each side, which secure the slide-in mounting brackets together. Then, remove the two nuts on each side, which secure the bumper to the bumper shock absorbers (having the car up on my lift greatly helped with accessibility to these fasteners). With these mere eight fasteners removed, it is now possible to step behind the car and slide off the entire rear apron assembly as a single unit. But be careful here, because the rear metal bumper is HEAVY - it caught me off guard and I nearly dropped the assembly when it came free from the studs on the bumper shocks.
Since my rear apron was to be repainted, it was necessary to detach it from the rear metal bumper. I set the assembly down on a big pad (to protect the finish). There are about ten plastic wedges, which captivate the apron to the bumper. You slide these out and then lift the bumper out of the rear apron. The side mounting brackets are easily removed by pushing out the pin rivets which secure them. And finally, the lower air diffuser slide to the right and lifts out
(after removing the five clips across the bottom).
I had both the rear apron and air diffuser refinished due to severe gravel pitting behind the rear wheels, which was present when I bought the car. The paint shop did a beautiful job and the color match (hellrot) was perfect. It is necessary to install new "foils", which are the black strips, which run horizontally across the rear apron (thin, narrow strip of black tape), and a fatter one, which runs across the air diffuser. I reinstalled the gasket which, extends across the entire top of the rear apron, and was ready to put it back on the car.
Re-installation was essentially reverse of above, but I note that it would have been of great assistance to have a second person available to help lift and position the rear assembly back on to the car. I had to wrestle with this for a few minutes to get both slide into the mounting brackets. Once in place, it was then a matter of reattaching the mounting bolts and fastening screws, followed by installation of the new wheel well trim pieces I'd picked up. Rear end - done and once again pristine.
Front end assembly
All I can say is that if you've never seen the nose assembly (and I mean assembly) off the front of an E31, you simply have no idea how complex the hidden engineering really is. What appears to merely be a nose assembly hides a very complex system of air ducting which, feeds the engine, the brakes, and the alternator. Re-assembling this system was a process of trial and error, because of the sequence of securing the rivets to the metal bumper. I'll explain this below.
Removal of the lower air dam
In order to remove the lower air dam, start by elevating the car and removing the two front wheels. With the wheels removed, you can now remove the forward plastic wheel well trim panels on each side. Removal of these will give you forward access. The lower apron is secured to the upper nose assembly by a single plastic wedge on each side and on small screw at the wheel arch, along with push in tabs along the front. So once you've removed the two wedges and screws, you can literally give it a tug from the front, and pull it off.
Removal of the nose assembly
The upper nose assembly is secured to the car by being riveted to the front metal bumper, which is bolted to the front bumper shocks. In addition, there are four screws, which secure the top of the apron, and these are visible from the engine compartment. To access the bolts, you much remove the front light bars (i.e., flash to pass lights). To remove these, pop out the black plastic inlet grill covers, and remove the two screws on each assembly, which secure the lamp to the nose. The bumper mount bolts are vertical, and are now visible and accessible with the lamps and grilles removed. Remove the two bolts, and the four upper screws. Then, depending on the condition of your car (e.g., how many time you've whacked into a curb or something, and broken plastic behind the air dam), there should be three screws, which attach the nose to the large air horn intake which extends up to the
kidney inlet grilles. Remove these three screws, and you should now be able to slide off the entire nose assembly.
Build-up of the front nose assembly
My car had several broken parts, which I had to replace - most from the "encounter", but several I discovered which existed at the time I bought the car. The sequence of assembly starts with reinstalling the two kidney grilles. For a more dressed up look, I bought two all chrome grilles, which were available as an option for the Japanese "Individual" market. These are installed from the rear of the nose, and really look great. Next, the metal bumper goes back into the nose (which I had refinished). The bumper is secured by rivets (this is where it gets dicey). I merrily pushed in all of the rivets, and then realized that other pieces needed to attach to the bumper (such as the big air accumulation boxes) were not yet installed, so I removed the rivets and then reinstalled them after assembling the air inlet system. You might be interested to know that the air inlet system is comprised of the two large air inlets boxes and a plastic duct, which connects the two boxes and runs flush along the front of the car. So I now have all this riveted together and then realized that the large air horn snout (which directs air from the kidney grilles down to the condenser and radiator and power steering cooler) must also be riveted to the bumper. So once again I remove two rivets, and wrestle with what is now a very oddly shaped assembly, and secure the air snout with two rivets. Now with all parts in place, the entire assembly can be reinstalled on the car. This requires extra care, because you have to line up several gaskets while you are sliding it into position, and additionally have to correctly line up the air inlet pieces. Getting everything aligned and in proper position probably took me forty five minutes before I could slide it back flush against the body of the car. I'm going to stop here for now, and will describe the rest of the reassembly in a follow-up message - my fingers are tired from typing 
and ya'll probably asleep by now anyway.
To briefly finish up my description of the reassembly of the front end of my 850, I'd like to mention a few other cosmetic things I did / had done. For those of you familiar with the stock front air dam of an 850CSi, you know it features an incredibly clunky looking front license plate box, large enough across for Euro plates, and protruding from the air dam by about two or three inches. Very unsightly IMHO. Solution? RD Sport (i.e., US version of real Racing Dynamics) sells a very slick grill insert, which eliminates and fills in the gap between the front light bars.
In some states, no front license plates are required, so I had the license plate inserts in mine removed and filled in. In addition, I had the body shop weld in plastic on the new front air dam to fill in the small locating hole on the front of it (for mounting of the clunky license plate bracket). They then sanded it down and painted both pieces, and you'd never know they originally had holes in them. Installing the grille insert in this manner totally transforms the front appearance of the car, making it look even sleeker and more sinister.
And I briefly mentioned them before, but they look so good they're worth mentioning again. There are all chrome factory kidney grilles available for the E31 now, and they look GREAT on our cars. Apparently these were originally offered as an "Individual" option in the Japanese market, and may have ended up on final production on Euro cars. They bring the nose of the car up to date with current BMW styling cues, without being overly bright or out of place. The only downside to these chrome grilles is that they are best mounted from the rear of the nose unless you have very long thin fingers such that you could reach through the grilles and properly secure them to the nose of the car with the mounting clips while pushing the snorkel air duct out of the way. They really need to be installed while the nose is off the car.
(By Steve Castle, January 2000.)
