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Custom Auxiliary Fuel Tank

I'm not sure if I really need an extra fuel tank. Maybe it's just that I've never seen one for a Connie that I liked; not that I've seen that many. I thought it would be fun to design something simple and within a nominal budget. As for esthetics, that of course is in the eye of the beholder. I've done one SS1000 and one BB1500 and maybe, just maybe, I'll do the Trans Canada Quest in a year or two. [ Update 1, I completed the TransCanada Quest - Vancouver, B.C. to Halifax, Nova Scotia, in 84.5 hours in June / 04]. [Update 2, I completed the Trans Canada Gold - Halifax, NS to Vancouver, BC in 70.4 hours in July/05 - 3633 miles ].

The first thing I did was to get a rough idea of the dimensions that were workable. Then came esthetics and minimal impact on the looks of the bike. I settled on a cell that would be about 3.24 U.S. gallons. Between angling the corners and metal thickness, I lost about 15% capacity and ended up with about 2.75 U.S. gallons. That's a 36% increase in fuel capacity. (See the table below for possible dimensions and their capacities.)

The weight of gas is about 6.1 pounds per U.S. gallon which brings this one to about 19 pounds soaking wet. While an additional weight up top of an already top heavy bike may not seem wise to some, I would point to those of you who ride two up, or those of you packing too many 6-packs around your belt. I'm guilty of a little of both occasionally and am not going to worry about it. Besides, it's meant to be filled up for riding at 60 mph+ not running to the 7-11 ( with your S.O. for another 6 pack.).

After a trip to the aluminum shop, the fabricator suggested the following design. After all, he says, "we don't want the tank to look like a lunch box, now do we." And, instead of my 3 piece mount, he suggest a one piece mount with two bends. I calculated the capacity lost to the cut off corners to be about  0.15 U.S. gallon. I think the trade off of capacity for esthetics is reasonable and the revised design is probably stronger due to the more oval shape.


This is sort of what the new FJR tank will look like.
 Courtesy of eMachineShop's drawing program

 

Here's the Version 2 of the tank just home from the fab shop. Actually, we did the finish sanding to clean up the welds a bit and on the flat surfaces to provide a little bite for the paint to adhere to.
The shop used 1/8" aluminum. I thought that would be a bit thin, but it's just perfect. This is version 2. Version 1 had a bolt in vented cap. The vented cap on version 1 sucked so on this model we bought an unvented cap with a weld in bung. The small bung is for the vent.

The tank is made from 4 pieces. The body is bent into its eight sided shape. Then the two ends and base are attached. The shop ground all the corners welds on Version 2. We used no filler at all. Any imperfections were hidden by the paint.

 

The shop couldn't put a baffle inside because of some problems with the metal buckling or something like that. When the tank contents start to drop, the baffle would stop the fuel from sloshing from side to side as the bike leans into the corners. Most fuel cell vendors sell foam which is stuffed inside the tank which should accomplish the same purpose. The baffle or foam really isn't needed as sloshing shouldn't start until the tank is partly empty. By then, the weight should be down and have less affect on the bike handling. After a couple seasons of riding and many thousands of miles with the tank in place, I never give it a second thought and never feel the affects of sloshing.

Filler cap

I wasn't entirely satisfied with the bolt in vented cap on tank Version 1. It seems that the bottom of the vent was immersed in gas when the tank was full. As pressure in the tank builds, gas is forced out the vent. I'm not positive about this, but I do know that the cap leaks. And it's scary since it drips so close to the exhaust.

This is the cap for tank Version 2.

As you can see, the cap sits just above the top of the tank which makes me much more comfortable.


 

Prep for painting

The really rough welding dribbles can be quickly cleaned up with a file. And then, surprisingly, a 150 disk on a random orbital sander did a pretty nice job cleaning things up from there.

Next, a little aluminum primer. I believe the shade is "Baby Shit Green". This is only one coat. Next, apply a little spot and glaze putty to make the seams pretty. No, I didn't have any choice in the color and no, it's not the final color.

On tank version 2 we didn't use the baby shit primer. We figured the sanding would provide enough bite for the paint.

Tank Version 1. 

Filled, more primer, sanded, and finished with that truck bed liner stuff. Supposed to be tough as nails and is a reasonable complement to the finish on the stock bags.

I wanted to use a stock Kawasaki filler cap but after looking at the underside, it only took about 2 seconds to see that it wouldn't work. There are caps made in Britain that lock but at 2 to 3 times the price. But if I need a replacement cap for my Ferrari, I'll definitely consider one.

Tank Version 2 

With the new improved non-vented filler cap. 

Note the 3/8" NPT bung for the vent. Next time I'll use a 1/4" bung. That's plenty big enough.

Mounting hardware. 

I talked to the parts department at the local Honda car dealer and they found these exhaust studs which are just perfect. I ended up not using the washers. I also wanted to put some sort of rubber cushion in the mount but with this setup, the studs just aren't long enough. The bottom nut is just a regular nut; the top nut is a Nylock.

The studs are in place. I didn't mount it flat on the plastic and bolt it down because those little black labels say that the maximum capacity of the rack that was there is 11 pounds. I assume that's because excess weight may break the plastic. With the studs mounted to the frame, 20 pounds of tank and gas hasn't been a problem... yet.
Mounting the tank

Here it is at home. I think the studs can go down a bit more. One reason that I like the studs is that I can raise or lower them to level the tank so that there is a slight slope down towards the petcock. It's not overly important and the movement of the bike will gradually get all the gas out of the tank. Besides, by the time you're starting to really worry about that last few ounces of gas, you should really be thinking about how badly you screwed up your fuel consumption calculations.

Vent

Here's the vent for tank Version 2. It's nylon and is supposed to be safe with gas. It'll connect to a tube so the vent will exit below the tank and should minimize spillage if the bike ever goes over.

As it turned out, I found a brass fitting

DO NOT put Teflon tape on the threads of the petcock before screwing it in. It gets all stringy if it threads in too far and will find it's way to your carbs if you're not careful. 

I called the tank builders and they suggested using a product that gas fitters use. They called it "white lead' which has been around for years. Just go to the plumbing supply store and get some pipe joint compound. I would suggest putting it on the last half of the male threads that go into the bung so loose bits don't end up inside the tank.

Petcock

I found this petcock after searching the web. It's from J & P Cycles and only cost $15. A Pingle petcock would have been nice but they're 5 times the price. I'll try this one first. It has a 3/8" NPT external thread which will match the bung that's welded on the tank. I removed the screen and cut off the brass tube which eliminates the reserve. Both the "On" and "Res" positions will empty the tank.

I have since found a Pingel petcock #1210-AH, far better quality, and has no reserve to worry about. About $56 U.S.  The J&P was pretty crappy and didn't take any time at all to become difficult to operate.

Antenna mount

The tank interfered with my CB radio antenna so a new one was quickly and easily made up and bolted to the bottom of the tank mount. (This is the Version 1 tank with the old bolt in cap.) 

The space between the tank mount and bike plastic left lots of room for the antenna mount. I like this one even better than my first effort a couple of years ago. This one is double thick 1/8" x 1 1/2" aluminum. It's double thick because over time a single thickness likely would have flexed a couple million times and I'm sure it would eventually fail. This one, being double thick, should be good for a couple million times.

Fuel filters

The plan is to put one of each of these filters in. The one on the right has the coarsest filter and will go in first so as to pick up the big chunks and help to stop the finer filter on the left from clogging up too easily. 

Here is a variety of possible dimensions that might work for you. If nothing else, it should save you a little bit of time with your calculator. Be careful as the table is based on the inside dimensions. You'd be surprised how big a difference the material thickness will be to the final capacity of your tank even using 1/8" material.

Fuel Cell Dimensions

Centimeters

 

Inches

 

Capacity

W

D

H

 

W

D

H

 

Liter

U.S. Gal

Imp. Gal.


35.00

20.00

17.00

 

13.78

7.87

6.69

 

11.900

3.14

2.61

41.00

20.50

14.00

 

16.14

8.07

5.51

 

11.767

3.11

2.58

40.65

21.60

13.98

 

16.00

8.50

5.50

 

12.275

3.24

2.70

 

 

 

 

 

 

 

 

 

 

 

50.0

20.0

10.0

 

19.69

7.87

3.94

 

10.000

2.64

2.20

 

 

 

 

 

 

 

 

 

 

 

40.0

25.0

20.0

 

15.75

9.84

7.87

 

20.000

5.28

4.39

40.0

25.0

10.0

 

15.75

9.84

3.94

 

10.000

2.64

2.20

 

 

 

 

 

 

 

 

 

 

 

35.0

25.0

20.0

 

13.78

9.84

7.87

 

17.500

4.62

3.84

35.0

25.0

15.0

 

13.78

9.84

5.91

 

13.125

3.47

2.88

35.0

25.0

10.0

 

13.78

9.84

3.94

 

8.750

2.31

1.92

 

 

 

 

 

 

 

 

 

 

 

35.0

20.0

20.0

 

13.78

7.87

7.87

 

14.000

3.70

3.07

35.0

20.0

15.0

 

13.78

7.87

5.91

 

10.500

2.77

2.31

35.0

20.0

10.0

 

13.78

7.87

3.94

 

7.000

1.85

1.54

 

 

 

 

 

 

 

 

 

 

 

30.0

25.0

20.0

 

11.81

9.84

7.87

 

15.000

3.96

3.29

30.0

25.0

15.0

 

11.81

9.84

5.91

 

11.250

2.97

2.47

30.0

25.0

10.0

 

11.81

9.84

3.94

 

7.500

1.98

1.65

 

 

 

 

 

 

 

 

 

 

 

30.0

20.0

20.0

 

11.81

7.87

7.87

 

12.000

3.17

2.64

30.0

20.0

15.0

 

11.81

7.87

5.91

 

9.000

2.38

1.98

30.0

20.0

10.0

 

11.81

7.87

3.94

 

6.000

1.59

1.32

 Conversion factors: 
1 inch = 2.54 cm  1 U.S. gallon = 291 cubic inches 1 Imperial gallon = 4.54 litres

Article By: David J. Morrow

Updated February 2007 

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