would this work...

So I have a tank that my father gave to me and I want to mount it on my 83 XJ750. The problem is the single back bone kind of turns into a triple back bone. The tank that I would like to mount is too narrow to fit the triple back bone. So I want to chop just a little off the frame and wanted to see your opinions if the frame would be as strong or would it hurt the bike too much.

Sorry for the picture mac doesnt have paint so I had to use a app on my droid, but this is my idea... the red being where I would cut and the green being where I would weld.

I would basically cut the sides of the "T" on the sinlge backbone where the two others meet and extend the backbone to about 3 inches from where the swing arm starts. Then weld the same "T" down there and viola... single backbone. but this would essentially eliminate the cross bars from the neck (dont know what they are actually called).

 

I wouldn't try it. But thats just my opinion i would rather put a new tunnel in the tank. I would hate to be riding down the road and the bike split in half. Not to say it wouldn't work but my life is not worth finding out just because i like the look of a different tank

 

Would you happen to know what a new tunnel would cost and where I could find one...?

 

You would have to make one. I figured if your welding was good enough to weld a frame you could bend up some sheet metal and weld it in to your new tank.

 

You really haven't given a detailed enough description of what your planning on doing to make an educated guess.

Do this and you can be advised: use a simple drafting program and create a line drawing of the existing frame in that area and what you want to change it to; or create a detailed drawing and take a photo of that and post it.

Just from what I could see you are changing the location of the main support for the upper frame. This would likely cause more torsion in the frame in that area which would be bad. The majority of the engines weight is right below and is distributed using that "triple backbone" so it looks risky. If you could somehow weld below and maintain the rigidity there it might work.

I would try and fix the tank myself or sell that tank and get one that fits better.

Like your new avatar!

 

dude just keep watching ebay for a tank, a 650 tank would fit too if you don't care about losing a little capacity I picked up this 750 tank on ebay for $85 - you could probably find one cheaper in a little worse shape. I definitely would not chop up a frame and jeopardize the structural integrity it to accommodate a gas tank for heavens sake. maybe someone on this sight has a dented/rusted up one they could offer you cheap??
just my two cents as well.

 

here is one for $16 which I think would fit?? little TLC and some rattle spray - might be able to make it serviceable and look ok.

http://www.ebay.com/itm/Yamaha-xj700-fu ... 35b62f61e0

 

Those 2 bars that you are looking to cut out are there to help keep the frame from twisting under hard acceleration and front suspension loads. Your entire fork assembly is supported by that small point of the frame.

While it is possible to do as you are thinking. You also need to make sure that you reinforce the area with gussets, and strengthen the backbone (solid round stock instead of tube). Flex, and twisting will be your two worst problems to deal with. Structural quality welding will be an absolute must.

What kind of liability insurance does your buddy have??

As was suggested. It would be better, and probably cheaper/easier to retunnel the tank unless you are looking to mount the tank frisco style (on top of the back bone). In which case. Just extend the center tube without removing the 2 outer support tubes.

The easiest way to retunnel your tank would be to find an old beat up, or rusted tank with a good bottom. Then use the tunnel out of it in your tank. 650 tanks use the same mounting, and are near give away items in the condition that you will be looking for.

Make sure you soak (vinegar) the tank before cutting/welding to remove any left over gas fumes. Sealing the tank will be required.

Perhaps some pics or identification of the tank might help get a better idea on how to mount it properly, and safely!!!

Ghost

 

This is the tank that I am trying to get to fit...

 

Here are some with it on the bike...

 

Altering the FRAME so that you can make a TANK fit is going at the problem: "Bass-akwards"

If you only want a Tank that fits, ... there are plenty to be had.
But, their NOT all on Ebay or Craigs List.
Sometimes you have to buy from a Salvage Outfit.

If you want a Custom Tank, ...
Start with one that fits and take it with your sketches to someone who can do the fabricating.

This place has a Multitude of Tanks.

DrumHill Cycle Salvage
Nashua, NH

 

I just like the style and lines of this tank... also Im not a fan of the stock tanks on these bikes. Just doesnt jump out at me, to each his own. Correct me if Im wrong but it seems that the only tanks with a wide enough tunnel to fit these frames are the Seca and Maxim tanks.

 

That tank is generally refered to as a peanut, or chopper tank. It mounts by tabs bolted into the recesses in the bottom of the tank, and sits somewhat on top of the backbone (frisco).

Retunneling that tank should be no problem to fit it down over the frame. get yourself and old trashed tank for the donor bottom and have at it.

If you find another tank like that. Let me know. I am looking for one for my project.

Ghost

 

Well I guess its back to the drawing board...

They have them on ebay for around $159

Looks exactly the same, and its brand new

http://www.ebay.com/itm/NEW-4-7-GALLON- ... 1e6859871f

would my maxim tank that I have on the bike work as a good tunnel?

 

OK, you're wrong. There are ALL SORTS of tanks that will fit these bikes, you just have to think "outside the box." There's a really cool European (Danish, Belgian, Norwegian, I can't remember) XJ900 Cafe bike that's bouncing around on the web that has a tank from a Bultaco 350 Enduro bike from the 70s, and it dropped right on. Tanks from some other Japanese bikes fit, but you have to do some poking about. The kind of fabrication that would be required to section your tank's tunnel into a tank like that would likely triple the cost.

 

So after setting the new tank on the bike again I decided to mount it Frisco style on top of the frame... and all I would need to do is relocate the petcock threads out a little more and fab up some mounts which would be a lot easier than re tunneling the tank or choppping the frame.

 

If you have a good sound tank (no rust, or dents) I would not cut it up. There are to many guys looking for good 750 tanks to fit on the 650's. You could sell your tank to offset the cost of the retunneling

It should not be hard to find an old beat up tank at a decent price. Unless you live near the salvage yard that I do.

Ghost

 

The maxim tank that came with the bike is all dented and was filled with bondo. So I doubt I could get much for it. But if I can figure out a way to fab mounts for the new tank then I shouldnt have to do any cutting.

 

I thought about modding my tank, but using the original tunnel. Just didn't know what type of metal was used to make the original tank which would affect the welds.
If you set the tank on top, you'll defiantly need to change the handlebars and control cables. Then you'll have to look at the exposed frame bars under the tank.
Altering the frame is possible if its done right and safely. Just have to know where to put the gussets and be a good welder, or take it to a machine shop and let them do it.

 

Your "Peanut" Tank is going to loose a considerable VOLUME when the Saddle Tunnel Mod gets done.

You'll also be limited to what Petc0ck you can use unless you have a Petc0ck Mod, too.

I have a feeling, ... for what you have in mind "Style-wise" ... that using a Stock Tank as the Foundation Element, ... modifying a Stock Tank to give you the Peanut-looking profile will require far less Metal-working and Welding.

If the Peanut Tank is close to a condition where it could be REFINISHED, ...
Sand, Fill and Paint.
Make it Beautiful.
SELL it to finance the acquisition and customizing of 6/750 Tank.

(( Knowing you are going to have the Stock Tank undergo some remodeling, ... allows you the OPTION of buying a DAMAGED Stock Tank at a discounted price. ))

http://www.drumhillcycle.com/Used_Yamah ... /3,3695615

 

Guys, I think he is saying that he has decided NOT to tunnel the tank NOR chop the frame, for the reasons you are talking about.

 

You hit the nail on the head maverick... I am going to mount the peanut tank (pictured above) on the bike frisco style, so no cutting or welding needed.

 

Here's a link to a bike where the three frame-rails were cut out and replaced by a single tube to do exactly what you want to do. you might be able to get more info by Googling around, or find a way of getting in touch with the guy who built it.

Hope this helps,

http://thekneeslider.com/archives/2010/ ... ansformed/

Nige

 

Nige, nothing was replaced. The guy simply hacked the two other tubes out of the way, and "prettied up" the amputation stubs. It's an accident waiting to happen.

We had quite a lively discussion about this bike recently, and there was some talk of starting a pool as to when it would self destruct; and whether it would break in half or blow up first (having not been re-jetted for the pods or anything.) Or spend the rest of its days going from show to show on a trailer; thankfully not being ridden to somebody's doom.

 

Ya that is scary to think that the bike could break in half as soon as you get on the throttle one day... and the tank would be sitting on top of the weld so you wouldnt be able to visually inspect it whenever you ride.