Installing an Aux Fuel Cell

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In July of 2005, Karl Marsh sent in the following description of mounting a gravity-fed aux fuel cell on his R1200GS:

At the recent Iron Butt Association convention I met Bill McAvan (http://www.blm-accessories.com). He was displaying a very cool 5.5 gallon Auxiliary Fuel Tank made to fit in the passenger seat mount of the R1200GS. I have always wanted 11 gallons of fuel so I knew I had to have it. The tank he made was designed for an R1200GS without the stock rear rack or the system trunk mount.

Bill let me take the tank out to the parking lot to see if it would fit my bike. I tried to fit it to my bike but it hit the rear rack. Bill took a look and decided that raising it up 3 inches would do the trick. He did so and sent it back to me and the fit is perfect. It is so nice to be riding down the road and when I see the countdown miles start to get around 25, I just reach behind me and turn the red lever and the tank slowly fills up to the top using gravity. This has increased my range to about 450-500 miles depending on my speed.

Installation Notes

The above picture shows the parts that Bill included with the tank as well as the other special tools needed for the install. From left to right.

Step-by-Step

  1. Drain fuel tank down to no more than 1 quart of gasoline. About 10 miles to go on the countdown.
  2. Remove right side plastic tank cover.

  3. Label the 2 lines coming from the bulk head circle so as to not confuse them later as shown above.

  4. Disconnect the main fuel line (quick disconnect style), and the 2 lower lines.

  5. Using the above diagram, remove fuel tank ring (#1) using special BMW tool for removing fuel tank ring. This is shown in diagram as number 16 1 021. The BMW part number for this tool is 90886161021. It costs $80.00.
  6. Once the tank ring is removed, it is possible to pull out the round bulk head (#2) out of the tank and bring it down just below the hole it came out of without disconnecting the hoses attached to the back of it.
  7. Carefully lower down the bulk head (#2) below the gas tank so you can drill the hole for the bulk head fitting on the bike.
  8. Using a #4 Uni-Bit, stepped drill bit, drill a 9/16" hole and create a slight beveled edge to the 9/16" hole by pushing up to the 5/8" portion of the stepped drill bit just deep enough for the o-ring to be able to seat. You can see where I decided to drill my hole if you scroll down to some of the other pictures.

    If I had it to do over again I would have drilled it 1/2" more toward the middle to allow more clearance for the 90 degree angle fitting. Be very careful while drilling this hole. You only get one shot at this. Also be careful to not get any of the plastic scraps inside the tank.

    Also be careful to not drill into the tank while drilling the hole. I held a 1" thick piece of wood behind the bulk head where I was drilling the hole to prevent the drill bit going into anything behind where I was drilling. I pre-drilled the wood with a 1" hole so that no saw dust would be created when the drill bit went into the wood.

  9. Now install the bulk head 90 degree fitting as shown above. Remember, I would recommend installing the fitting about 1/2" further towards the middle than I did. It works fine the way I did it but you will have an easier time if you follow my recommendation. Place the bulk head back into the tank and replace the fuel tank ring. Tighten the ring using the special BMW tool. Reconnect all the hoses.

  10. Now it is just a matter of running the gravity hose back towards the auxiliary tank.

    The above picture shows how I routed the hose.

  11. Next install the quick disconnect fitting as shown above. I left a little extra hose so that when the tank is disconnected I can just shove the fitting under the rear rack where the U- lock goes.
  12. Now you just have to route the vent hose and the ground wire. I used quick connects that Bill included to allow for easy removal of the tank.

For more pictures of the tank on the bike, go to http://rc46.smugmug.com/gallery/615064

For other questions email me (Karl).

A few more photos...

Copyright © 2005-2007, by H. Marc Lewis. All rights reserved.