'80 Yamaha XS 400 Cafe / Fighter

PancakeShake

Been Around the Block
So here is my second solo project.

I bought this ’80 Yamaha XS 400sg as a bobber project. Had a handful of parts but still a good amount was missing. Along with the missing parts, it had a homemade wiring harness that was barely half way complete. I was able to pick it up for $300 so I looked through the mess and saw a sweet café bike…somehow.

Brought the bike home and did the typical breakdown. Stripped it down to the frame, cleaned up some of the parts, took a look at all of the “iffy” looking welds and parts.

After the breakdown I made a hand sketch of what I kinda wanted the bike to look like, pinned that to my bench and went at it.
First I decided to get the frame on its feet and get it to a place I liked. Made a quick model in CAD and using some basic dimensions from the frame I was able to get some lines I liked in places they would fit. Then I headed to Ace, got some tubing and got started. I have a small 200amp TIG welder at home I use for bike frames, and was able to get the messy welds cleaned up nice, and get my new frame pieces in place. After about 2 days I got the frame to a place that I liked, but the stupid shock mounts took me a solid week to get finished. Once the shock tabs were cut, welded, and mounted I built up the bike and felt the geometry. Felt great, but the moment on the rear swing arm was too great for the dinky coils, so I upgraded them to some beefy coils from McMaster.

After the frame was in a good place I whipped up a seat pan. Same deal, made it in CAD, converted to sheet metal, printed it out, traced, cut, welded. IMO, it came out great. Fit nicely and looked just how I wanted it to.

After I had the seat done I moved onto making some foot pegs for the bike, as well as a pair of flat “fighter” bars for it.
Next was paint.

I have always loved the red frames on Monsters so I decided to go for it. I don’t know about you…but I love it. I think it’s perfect having the frame be the accent while keeping everything else sleek and black.

After the paint was done, I headed down to Coopers to pick up an exhaust and a headlight. Found a MINT 2-to-1 exhaust for the bike and it looks and sounds great. Headlight was from an older GS and bolted right on to the fork tubes I got there as well.
Now that most of the parts were there it was time to conquer the beast…electrical.

Started from scratch. Took a wiring diagram in one hand, beer in the other, and went for it. Took a full afternoon’s work, but I got it to a point where I felt comfortable putting 12v to it. Hooked it up…and it wasn’t quite right. One plug was always ON. Made one quick post on the forum, and realized you CANT use a battery charger IN place of a battery. Its AC I guess, never knew. So I hooked up a battery and whaaa laaa! “Crank, crank…put put put!” Started right up.

Pretty pumped at this point. I started the boring finishing work. Made a clutch cable, made a new throttle cable, made a new LED blinker / tail light piece, wired in the headlight and started cleaning things up along the way.

However, someone made me an offer I couldn’t refuse so I sold it

I think it came out pretty nice for my second project. Lemme know what you think.

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Looks great! If you dont plan on running a tach, let me know if you need one of these.

http://www.dotheton.com/forum/index.php?topic=38853.msg422786#msg422786
 
Is the frame strong enough where it bends back where it won't buckle if you hit a big bump?
 
Toast said:
Is the frame strong enough where it bends back where it won't buckle if you hit a big bump?

Oh yeah.

.085 wall, 1" chro-mo tubing. It was all TIG welded so the heat control only adds to the overall strength.
 
er, no...

This is an unsafe design, please don't ride it.

the main function of the frame is to keep the wheels in the same plane, your frame modification prevents this, the fact that it's a poor geometric design can't be compensated by the use of stiffer (not stronger) materials. and no weld adds to the strength of the parent material, especially with 4130. a good weld will be the last place to break when destructively testing a part, but only because the weld is thicker than the base metal. I have a feeling I'll get a rafting of shit for calling this out, but you've really gone and created something dangerous.
 
I have to agree with you Sean. Too many weak points in the rear section of the frame for my taste. I really do applaud the effort and out of box thinking, but this design scares me.
 
Roc City Cafe said:
the main function of the frame is to keep the wheels in the same plane, your frame modification prevents this,

And how does adding a different sub-frame or seat effect the wheels being "in plane"? The riding geometry has not been changed at all. I kept the head angle the same. The only thing different here is the elevated seat.
 
it's because all the structure holding the steer tube in proper relation to the swingarm pivot is missing, you more or less made the structure between those two parts into a spring...
 
Count me in on the "beautiful execution, structurally unsound" bandwagon. You've made a frame that is going to flex much more than before, and not in a balanced fashion.
 
Agreed with stated, that frame is now a death trap. Also the position of those shocks does not make sense to me. thake that zig zag out and make it straight again.
 
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