Single Backbone Conversion

Hello All,
This is my first post here…I recently picked up this project that Rogue had started:
http://www.xjbikes.com/forums/index.php?threads/1981-xj650-alaskan-bobber-project.40384/#post-354973
I'll be updating that thread as the project moves along, but I wanted to make a thread specific to a single backbone conversion. As you are all aware, custom tank choices are pretty limited for the XJ without doing major modifications, due to the triple backbone style of the frame. I purchased a Cole Foster tank, and didn't really want to hack up the tank or have it sit high on the backbone, so I decided to convert the frame to a single. I've searched all over the forum for detailed pics of how people have done it, but couldn't find anything that was really helpful. Hopefully this thread will be helpful for those attempting to do the same thing. I'm sure there are many ways to do this, but this is how I did it.
First off, I purchased a 24" long piece of 1 5/8" x .134 wall DOM tubing. The ID of this tubing will allow it to snugly fit over the original main top tube. I know this seems overkill, but I like that fact that I can sleeve the oem tube for strength and continuity. The bike has already been hard tailed by Rogue and he did a great job, so I didn't want to redo any of his work. In the pics you can see that I have cut the top tube directly in front of the coils mounts and also separated it from the double tubes. Do not cut the double tubes from the frame at this time, they need to remain until the new top tube is welded in to prevent the frame from distorting. Also, it goes without saying, that the engine needs to be removed from the bike before cutting anything.

-Todd

 

Ok, so these next pics show how the new top tube was notched to fit at the neck and new cross brace at the rear. The cross brace is 1 1/4" .125 walled square tube that was notched to fit snugly.






And here is how it looks fitted to the frame-

 

And here is some more detail before welding-

 

And here is what the frame looks like after welding and fully removing the twin bars-












I was originally going to add a piece of 1" tubing from the neck to tie in under the top tube, but I really don't think its necessary. I may gusset the rear cross brace and the twin down tubes.
I will likely plug the 2 uprights with a bullet style plug for strength and cosmetics.

-Todd

 

I'll be watching this one. You did a good job with that mod.
Some questions have been raised in the past over eliminating those side backbone pieces, whether it will allow the frame to twist or not due to the way the motor sits in the frame. You may want to add a piece under the backbone or some gussets to eliminate the twisting possibility.

 

Nice job! I second the gussets. Not a big deal since you are already in there. Sort of like a small fish tail at the bottom end of the backbone. Suppose now you can shape out some of the lower gusset on the neck? I'll be going down this road myself next summer when I continue hacking on my venerable old 650 frame. Oh yeah...tank selection here we come.

 

can't wait to see how this all comes together. nice fab work.

CN

 

Any updates?

 

Would have liked to see how this turned out. Are you still around Todd???

 

Build thread is here:

http://www.xjbikes.com/forums/index.php?threads/1981-xj650-alaskan-bobber-project.40384/#post-354973

 

Thank you