X-Brace (eng)

Watching all the interchanges in respect to inserts, nutserts and rivet nuts caught my interest. Based on the confusion, I was hesitant to install the X-brace on my cars. I apologize for the length of this article, but based on the problems some people are having, I feel that the content is relevant. If it bothers you, keep in mind that this forum is a multilevel experience sort of thing.

This can't be that difficult. Turns out, after some investigation, that it isn't. I'm told that 10/94 and later M3's come with the inserts already installed. If your M3 is earlier then this, take a look underneath and check. [On my 10/94 M3 I wasn't able to tell by sticking my finger in the hole, once I put a 13mm - M8 bolt in the hole it was obvious that there were threads there. - Dale] The BMW style rivet nut (not insert) part # 51 71 8 175 003 is similar to the AVK RN series rivet nut, but different in dimension.

The design application for the AVK rivet nut is chair leveling legs. I have no idea why BMW chose a rivet nut for their X-brace application. I look at an insert or rivet nut as something that holds the nut in place till I get the bolt in. Based on my tests and the cost of the proper AVK rivet nut tool (didn't know at the time), I chose to use the AVK AK series insert instead of the BMW rivet nut to install my X-brace.

Thinking about it, since the BMW rivet nut is different in dimension compared to the AVK rivet nut, I'm not sure what the proper tool for the BMW rivet nut is. In my tests, I installed an AVK AK series insert in a piece of .070" steel using the AVK AA170 pliers tool. The recommended assembly torque for the AVK AK series insert is 15.5 LB-ft. I applied 50 LB-ft with no spin out or insert thread failure. When I went to 55 LB-ft, insert thread failure occurred, but no spin out. I also installed a BMW rivet nut in the same piece of steel accommodating the 90 degree taper of the rivet nut, using the same AA170 pliers tool. This is not the recommended tool but it seems to work just fine (see below). Based on my experience it takes less force compressing the BMW rivet nut than the AVK insert. Since it takes less force, I wouldn't worry about breaking the AVK AA170 tool if you decide to use the BMW rivet nuts. Recommended assembly torque for the BMW rivet nut is 20 LB-ft. I applied 35 LB-ft with no spin out or thread failure. When I went to 40 LB-ft thread failure occurred, but no spin out. I did the same test installing the insert and rivet nut using the AVK expendable tool. With the AVK insert the bolt broke at 40 LB-ft (bad sample:)). With the BMW rivet nut thread failure occurred, as above, at 40 LB-ft. As above, no insert or rivet nut spin out occurred. I also installed the BMW rivet nuts using the AVK pliers and expendable tools "WITHOUT" accommodating the rivet nut 90 degree taper. The larger inner ridge of the AVK tools does not fit within the BMW rivet nuts. To prevent marring the face of the BMW rivet nut, place a washer between the pliers tool and the rivet nut. With the AVK expendable tool just turn the contact piece around to prevent marring the BMW rivet nut. Although I expected spin out, as above, thread failure occurred at 40 LB-ft with no spin out. After performing my tests using the AVK tools, I have no idea why people are having trouble with spin out. My guess is too large a hole, not removing the cosmoline or not compressing the rivet nut enough. You decide if you want to go the AVK insert or BMW rivet nut way. Based on my tests, either way will work fine. If not knowing, and you were to compare the two, side by side, my guess is that you would choose the AVK insert. It's just a better nut holder in my opinion.

There are three holes (per side) in the front portion of the BMW X-brace that line up with the three holes in the front axle support on my ti.

For some reason (non M3 and M3's up to 10/94) the holes in the front axle support .390" do not accommodate the .431" BMW rivet nut. The rivet nut you purchase from BMW is too large for the holes in the front axle support. If you look up the part # for the convertible front axle support (which comes standard with the X-brace) the same part # is specified for all E36 models. The same source lists the rivet nut mentioned in the below parts list. I can't believe that BMW enlarges the holes in the front axle support when a convertible comes down the assembly line. To do this right using the BMW rivet nut you will have to enlarge the holes in the front axle support to .433" using a 11 mm drill and create the 90 degree taper in the front axle support to accommodate the taper of the rivet nut. The rivet nuts on the '98 M3 that I looked at sit flush with the surface of the front axle support.

Due to the added wall thickness of the rivet nut, AVK does not sell an expendable tool to accommodate their rivet nut. As mentioned above, the AVK expendable insert tool, that I purchased just to see how it works, works fine in setting the BMW rivet nut. It is not as convenient to use as their pliers tool. If you purchase the AA170 pliers tool you can use it for other applications by just purchasing the conversion kit for the new application. Any application equates to any size threaded insert you may want to install. As a side note, the twin handle tool that AVK recommends for installing their rivet nuts is part # AA480 which sells for $208.67 with the M8 conversion kit. Keep in mind that this tool will not fit the inner opening of the BMW rivet nut either. This might explain why the non-rivet nut T-handle tools are breaking. I really don't know. The T-handle tools are for the AVK AT series swedge type inserts.

I started out at my local nuts and bolts place (E&F). They carry AVK inserts and installation tools. The counter man said that they do not do metric. Here we go. I called AVK in Valencia, CA 1-805-257-2329 (they don't want to be bothered either). They referred me to Mr. David Lang 1-609-866-2118, who is the rep for the CT area. He sent me a catalog and referred me to someone at E&F who will do metric. Based on pricing, a web site, a nationwide reference with an 800 #, I purchased (at the time) my AVK tools from Reid tool 800-253-0421 (www.reidtool.com). The problem with Reid tool is that their AVK insert minimum quantity is 2000 (they would have to bring in that quantity to sell you four of them). After negotiating with many, HWE (HW Eckhardt) 1-888-492-4152 agreed to sell us a small amount of the AVK AK series inserts (they stock them) and the tools set up as kits. Ordering a small amount of inserts from anyone, doesn't cover their invoice cost (I'm told). HWE (Jackie) agreed to set up kits for us. Kit # 1 AVK-0515 includes the AVK pliers tool and conversion kit with 8 AVK inserts for $58.96. Kit # 2 AVK-0516 includes the AVK expendable tool and 8 AVK inserts for $11.00. If you have the tool and just want the inserts (Jackie really didn't want to do this), 10 inserts from them for $10.00 is the best I could do. Their minimum, like others (except in our case), is normally $50.00. Jackie says that any of the above items are available only via a VISA or Master card order. If you wanted to get together as a club thing, I'm sure Jackie would sell you the tools with as many inserts that you needed.

As mentioned earlier BMW uses a rivet nut similar to the AVK RN series rivet nut. The below parts info shows the part #'s for both the BMW and AVK stuff and the necessary installation tools. You decide which style you want to use and pick the parts accordingly.

Purchase the BMW parts from your favorite supplier.

You basically are removing the stock rearward cross brace and replacing it with the X-brace. The rear of the X-brace mounts to the same (two) threaded M10 holes as the stock cross brace. The front of the X-brace mounts to the four M8 AVK AK series inserts or BMW rivet nuts that you will install. The convertibles and roadsters that I looked at used two bolts per side. There was no middle hole in there X-brace. As expected, the stock cross member that you remove was not on the convertibles and roadsters that I looked at.

The following is just a guide. Read it completely before attempting this modification. I completed this modification on my '97 318tis (build date 4/9/97). If your car is different, modify the following accordingly. As always, feel free to do it your way. Here we go:


BMW stuff

1 each Cross reinforcement, part # 51 71 8 410 212 $139.00 retail

2 each Bolt w/washer M10x35, part # 31 10 1 095 140 $0.77 retail

4 each Bolt w/washer M8x20, part # 07 11 9 915 093 $0.17 retail

4 each Rivet nut part # 51 71 8 175 003 $0.63 retail


1 each Drill bit 11 mm 135 degree to accommodate the BMW rivet nut. The larger the angle of the drill the more likely you will end up with a round hole. J&L 1-800-521-9520 PTV-16310-A $10.06.

1 each 90 degree six flute (less chatter) counter sink bit to create the 90 degree taper in the front axle support to accommodate the BMW rivet nut. J&L SIX-96016-D $7.89. J&L requires a $25.00 minimum. If you don't purchase from them, call for a free catalog. An excellent metalworking tool supply catalog reference.

AVK stuff: From Reid Tool 1-800-253-0421
    1 each Pliers tool, part # AA170 $39.68 with
    1 each Conversion kit, part # 271AA271-8125 $8.63
    1 each expendable tool part # AA184-8125 $4.16
    4 each AK series inserts part # AK-S-4-8125-3.8 
      $0.27each (2000 minimum) What!!!!!

   AVK stuff: From HWE 1-888-492-4152 (Jackie)
    1 each Kit (AVK-0516) AVK AA170 Pliers tool and AA 271-8125
           conversion kit with eight AVK AK series inserts
    1 each Kit (AVK-0515) AVK Expendable tool AA184-8125 with 
           eight AVK AK series inserts, $11.00.
    10 each AVK inserts AK-S-4-8125-3.8, $10.00

    1 each Drill bit 17/32" 122 degree, with turned down (1/2") 
      shank, Hanson/Irwin # 90134 $20.49.  J&L supply
      1-800-521-9520 PSD-91434-E $14.53 $25.00 minimum.        

I double chocked both rear wheels using Tru-Cut WC2 wheel chocks. I modified my chocks by chaining each pair together using chain and 1/4 - 20 hardware (the details of this will be in my, in the works, lets jack it up article). Place the car in gear and set the emergency brake. I jacked up the front of my vehicle, placing my jack centered at the front cross member just forward of the oil pan sump. Once up in the air I placed my Tru-Cut UR6500 ramps under the front wheels. I backed this up with my jack stand adapter/jack stands under the BMW jack pads. I assume you know what happens if the system you choose to use, fails.

Remove the stock cross brace using a 16 mm or 17 mm whatever, depending on which size your car has. BMW cautions: Do not drive the car with this piece removed or the mounting points might not line up when you come back.

The hole size for the AVK M8, AK series insert is 17/32" or 13.5 mm -0 + .004. Enlarge/Drill the four holes in the front axle support (two holes on each side) (the middle hole of the three holes that line up with the X-brace on each side remains untouched). Remove any residue flashing from the drilled holes. Take the time to clean the cosmoline from the holes on the front and back surfaces.

Install the four front inserts using a tool similar to the ones I purchased or the suggestions of several digesters. Its your choice.

Follow the instructions that come with the AVK AA170 pliers tool. Make a point of tightening the conversion kit to the tool. This way you can turn the knurled knob of the tool either way without the conversion kit coming undone. If you don't, you have to turn the handle to get it out. On the car, there is no room to turn the handle. Oiling the moving parts of the tool is also recommended. Keep the oil from the threads of the conversion kit. The AVK expendable tool sells for $4.16. You can duplicate this expendable tool with a hardened bolt, washers and nuts. For $4.16, why jury-rig it. The AVK AA170 tool and the M8 adapter I purchased sells for $48.31. When your done using it, sell it to the next guy for $48.31. I'm keeping mine.

So that you don't end up with a partially attached brace with spinning inserts you can do the following. Take a small piece of 1/16" thick metal and drill a hole in it to accommodate the M8 bolt. Test each insert to see if you can torque the M8 bolt/washer to 15.5 LB-ft (20 LB-ft if you use the BMW rivet nut) without the insert spinning. If this works out position the X-brace and bolt it in place. Based on my tests, which were described above, I skipped the above step with confidence.

The torque for the M8 bolts that are used in the inserts (13 mm socket) (12 mm on some cars) is 15.5 LB-ft The torque for the M10 rear bolts is (16 mm socket) (17 mm on some cars) is 51.5 LB-ft.

In summary, the AVK tools will work with the AVK AK series insert or the BMW rivet nut. If you properly prep the holes and set the inserts / rivet nuts, this how to is really a piece of cake.

When your done, go for a ride and see whether your car, or you got stiffed. I rationalized that it will protect the sump :). If anyone in the CT area wants me to help them install one, in my heated/AC garage, using my stuff, let me know. My labor rate is not the same, but similar to Duane's :).

Thanks go to David Lang from AVK for providing the information and his complimentary bag of 25 inserts. Also, Wes at Reid tool for his willingness to sell me the tools without the minimum bullshit and Mr. Echardt of EWS for his willingness to sell you $2.00 worth of AVK inserts for $10.00 which sort of covers their invoice cost. Based on that, if you go the AVK insert way, I would also purchase the tools from him. Lets not forget Ron Katona whose going nuts with nutserts articles prompted me to come up with the above.

Ron@unofficialbmw.com, FLI BMW, FLY BMW, Marlborough, CT