This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your BMW 3 Series. The book contains 272 pages of full color projects detailing everything from performance mods to timing the camshafts. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any 3 Series owner's collection. The book was released in August 2006, and is available for ordering now. See The Official Book Website for more details.
Many E36 owners upgrade their chassis with the factory crossbrace that mounts underneath the engine. This crossbrace was installed as stock equipment on all convertibles and the 1995 LTW, a lightweight version of the M3. The convertibles received this bar to stiffen up the chassis since their chassis are naturally less stiff than coupes or sedans because they have no roof.
Installing the crossbrace on a standard E36 coupe or sedan serves a dual purpose: The crossbrace stiffens up the chassis and also protects the engine sump from road hazards.
|4||07-11-9-915-093||M8x20-Z1 Allen bolt with washer|
|4||51-71-8-175-003||M8 blind rivet nut (nutsert)|
Installing a crossbrace is quite easy; the only difficult part is installing the inserts that attach the crossbrace to the front axle support bar. M3 cars manufactured after October 1994 already have these inserts installed. For all other cars, the holes are predrilled in the front axle support bar, but you will need to install the inserts.
The inserts corresponding to the crossbrace are called "blind rivet nuts", or "nutserts".The nutserts are installed into the front axle support bar and compressed against the sheet metal so they don't turn. They support loads from the attachment bolts.
First, jack up the front of the car and support it on jack stands (see our article on jacking up your BMW). Identify the four holes in the front axle support bar and remove any dirt or debris that may have gathered in them. Test-fit the nutserts into the holes. If they don't fit, chase the holes with a 7/16-inch or 11-millimeter drill.
Now, install the four nutserts into the holes. Use the procedure outlined in Photo 3. Check to make sure the nutserts are installed tightly and do not rotate in their bores. If they do rotate, pop out the insert and try again with a new one.
With the inserts installed, remove the support bar that runs just behind the rear of the engine sump. The crossbrace replaces this bar. Bolt in the new crossbrace and apply blue Loctite Threadlocker on the threads of the bolts as you install them. Tighten the larger rear bolts to 70 N-m (51.5 ft-lbs) and the smaller ones that mate with the nutserts to 27 N-m (19.9 ft-lbs).
There has been some talk in BMW circles about the benefits of welding the crossbrace in place. This is not a good idea, as it would require you to cut out the crossbrace if you needed to drop the oil pan to replace a seal or your rod bearings.
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The factory lower support brace stiffens the chassis and provides undercarriage protection, especially for cars that have been lowered.
The E36 convertibles all have this brace installed as stock equipment from the factory. The crossbrace replaces the single cross bar installed as standard equipment on nonconvertible E36 models. The cross bar mounting points are shown with yellow arrows. The new nutserts need to be installed into the front axle support bar in the locations indicated by the blue arrows. As you can see, the crossbrace installed in this car has done its job--the bottom is scratched with scars from battles with the pavement. The bar also protects the bottom engine sump.
Installing the nutsert is the most confusing part of this relatively simple project. This photo sequence shows exactly how they work and how to install them without special tools.