Motorcycle Brat/Cafe Subframe

[seanile]

hiyooo. here's what ive been doing with my amateurish tig skills as of late.

i wanted to take this bike (yamaha star bolt):


and put a 2-seater bench seat on it. it's already got mid controls, a clean line at a good height from the tank backward, and plenty of mounting points to choose from for things. the ultimate goal though is to not touch the frame itself, just make this a bolt-on situation and keep it capable of easily being reverted back to stock.

here were a few mock-ups i did to get a feel for the size, lines, and structure of it all.



this one i could actually sit on



after months of delaying and thinking, i started work last weekend.
1st step was a battery cover. it's secured where the stock seat is held in place, as well as the two un-used bolt holes near the rear wheel well.


next was bending and shaping some mounting tabs, and then coping and welding the front end of the seat structure to it...despite my amateur welding skills, im proud that i only put one hole in the tube AND was able to fill it :D


the core of the subframe followed


the next day i made some great progress and the frame is now mountable, just need some vertical support struts and am starting to work on the electrical mounting and routing. i want to re-use the stock lights so it'll be interesting figuring out their positioning.
the "jig" i came up with is a boat strap keeping the two extensions at the front pressed against the core of the frame. the round file threaded through the mounting holes to help maintain the pressure and the spacing. the horizontal tubing theyre resting on helps keep a uniform height across the frame.


the vertical tube is just to prop it up for the time being.



i was really proud of my welding that day..ive come a very long way


yesterday saw this come together:

it's a storage box for my tools and registration that'll hang under the seat and has a cutout for wheel clearance. the electrical wires will also be routed through it on their way from the lights to the battery. also surprised i didnt put any holes in that given it was 20ga sheet metal and i was doing a fair lot of butt welds.

[Too Tall]

Far out. Some Yankee ingenuity going on in Ohio.

[seanile]

hah, i guess it helps im from NY and went to school in Boston?

[72gmc]

Cool project. I would have scope creep issues. "What if the fender looked like this..."

[seanile]

^yea, i'm having that with the "how should i mount the rear lights?" way, way too many options..and none of them quite make the most sense yet.

tonight i cut and capped the protrusions on the front half of the seat frame:


also trying to figure out how to cope this evenly

[seanile]

well hot dog, check this out!
this took a whole lotta guess work and im stoked it fits 98% well enough to weld :D

[seanile]

today's progress, welded that^ foil on



and made a light assembly. still don't know where to put the license plate though where it'll have enough wheel-clearance.

[seanile]

hooray! tough part is pretty much over.
shaped and capped the open ass-end. the curved caps interface quite nicely with the backs of the turn signals


just have to weld on the light mount, the struts, and the toolbox, then route the lighting and get it painted.

[seanile]

been a little while waiting for new tungsten electrodes and the dropouts i'll be using for the strut mounts.

today, put together a new, wider version of the light/license plate mount. also re-did the "tool box", and put some seat pan mounts on it.
tomorrow, coping and welding the struts.
sometime during the week i'll have to get some stainless steel and will shape the seat pan and drop it off to be upholstered.
then, if it all works out, off to powdercoat.

[seanile]

mounted!
struts were horribly out of alignment, specifically the left one, and it was unfortunately very preventable..pain in the ass to get to an acceptable plane, but i got it there. and i just rode it around a short bit..feels great even without a seat haha
used paragon dropouts for the mounting portion.

[seanile]

cut a big chunk out of my bench top to make the seat pan haha. i wanted it stainless so it could withstand any roadspray. figured i'd use what i've got!


shaped it and welded some stainless bolts


my no-fucks-given electrical stylings


off to upholstery tomorrow

[nahtnoj]

This is so you can bring a woman with you? Worth it.

[seanile]

That was a big part of it :)
Coupled with me being too cheap to spend hundreds of dollars on "kit" parts to make it a two seater (ive always wanted a bike with a bench seat anyway, which there were no kits for), and wanting to give myself something real to refine my very amateur welding skills instead of just joining scrap tubes for eternity. Ive gotten exponentially better than i was when i started, which is very encouraging, but yea, still very much an amateur hah.

[seanile]

got some clubman bars installed while i wait for the seat

[seanile]

i gladly present to you, the final product until i can afford a new exhaust and air intake.
at most i'll be fab'ing some passenger pegs, but for now i'm done :)

[SlowPokePete]

Amazing transformation...thing looks wicked cool now.

Nice job!

SPP

[seanile]

thanks!!

[lumpy]

Cool. Great project.