Very nice Ron. ::008:: I look forward to reading what your new capacity is.
As someone else that went through this process, I can add a few comments. Welding thin wall steel is tough. Grinding the welds after can easily result in pin hole leaks, which adds to the fun of checking for leaks and re-welding, re-grinding, etc. Not everyone is up to the art of welding thin wall materials.
My expanded tank follows the same lines as Ron's. I have a capacity of 8.2 gallons. I did a few things different, which partially comes down to the fabricator I used and partially my background in industrial manufacturing. I chose not to coat the inside. OEM tanks are not coated. Paint can be expensive. I chose to have the tank coated with LineX which is gas proof and more durable than paint. (I checked the tank with gas for leaks prior to having it coated with LineX on the outside. The LineX is also a secondary leak filler, but wasn't necessary for that purpose, at least when the tank was new.) It's not a look everyone would care for though. I'm very much a function guy. ;D My tank ended up costing about $1100 total. Buying a used tank in good condition, paying a fabricator $600 to strip, expand and weld. leak check, etc and another $220 to have it primed and coated with the premium LineX at a local shop. All of these costs are variable.
Just finding someone to do the welding is not as simple as it sounds. It's a challenging and time consuming job. Most of the welder/fabricator people I've talked to that have done this did not fully recognize how challenging and time consuming it would be. My fabricator said he wouldn't consider doing another one for less than $1000 and I suspect he would charge more than that. And that's just his cost, not the cost of paint or buying the donor tank. If you buy a dented tank, add some time to fix the dents too. I was fortunate to have a strait up fab guy that stuck to his original cost quote, though it took him 2 months to finish the tank, not the two weeks he originally though it would take. I didn't press him on the time line until a month had passed. I didn't have a pressing trip coming up, so could accept the relaxed time line.
Because of the process of sectioning the tank and raising the top, the two metal vent lines inside the tank need to be lengthened. My guy had some ideas, but I pointed him in a different direction, removing the brazed in oem lines completely and replacing them with new metal lines fabricated from steel automotive fuel or brake line. This made it easy to source the lines and easy to bend. Re-attaching them to the tank was more challenging for him. Brazing is not as common as it used to be and the heat from welding can impact the brazing.
Note: If the new lines stick out the bottom of the tank more than the oem ones did, then the hoses will bind when you try to set the tank down in the frame. I had to trim mine a bit as the fab guy left them a bit longer than stock.
I've had my tank in use for a while w/o issues. 300 mile range plus reserve. I think I have seen 320 or so a few times before reserve. It meets my current needs of matching the range of my wife's '16 BMW GSA with it's 7.9 gallon tank. She gets slightly better mpg than I do, (maybe it's S mode, or just my wrist?). I still miss the 11+ gallons I used to have sometimes. All in all, mounting a fuel cell to add to your range is cheaper than building an expanded OEM tank. Each method has benefits.
Another cautionary note; Watch your handlebar clearance if you build an expanded tank. It's very easy to end up blocking the bar swing. Mine works fine with my Rox 2" risers, but would not work with stock height bars. I knew that during the fab process, so considered and accepted this aspect of my build. There are things I would have altered in the design to make it more attractive, but it works like I wanted it to work, so I have no regrets in the work done.
A Search for 'supertank' will find some photos of mine on this forum.
There is a thread on my custom 4.8 gal flat bed fuel cell here:
http://www.yamahasupertenere.com/index.php?topic=5810.msg101554#msg101554
I too have a perfect red tank sitting in a box. I'm not selling mine though. Eventually when I move on, the stock tank will go back on the bike and the supertank will get sold. I've found it to be a lot better return on high mile bikes to put them back to stock before selling and sell the farkles separately.
