AfterBurner Chopper - Section 1
Section 1 |
Featured on Makezine.com and Instructables.com ***
Take a basic mountain bike and transform it
into a 1970s style chopper in a weekend.
1970's style chop was named and built by Enzo and Nathan (father and son team)
from an old mountain bike that was found laying in the mud at the city dump.
Instead of the extended front forks, this chopper is roughly styled after the
classic Raleigh Chopper bicycle with the straight frame and tiny front wheel.
This project requires no extra tubing in the frame, and except for a few small
add-ons, only requires cutting and welding two frame tubes.
bike with 26 or 24 inch wheels can be used for this project. In addition to
replacing the seat and handlebars, you will only need a front wheel of any size,
but it should be smaller
than the original rear wheel. A 16-inch wheel was chosen for this build.
The donor bicycle (Photo
1) is the typical garden variety steel framed mountain bike.
This frame is described as "uni-sex", but looks kind of
"girlie" to me.
Don't worry about it, dude, when we are done, that won't be the case.
The overall condition of this bike is fairly good considering it
sat in a mud hole at the local dump, and was probably run over a
dozen times by the bulldozer guy. This is a good thing, since
we will be using everything but the front wheel, seat and
Photo 1 - A typical steel frame mountain bike with 26-inch
All of the parts are stripped and checked for damage (Photo
2) before the building process. Everything looks good so far,
minus a rusty chain which will be used in ways a chain was not
intended for later.
Photo 2 - Taking it all apart.
To install a small 16-inch
front wheel yet keep the frame looking somewhat like the original,
something has to be altered or the pedals will certainly be
dragging on the ground. Longer front forks would do the trick, but
since that isn't the focus of this project, the only other
option is to raise the bottom bracket.
To get the bottom bracket up higher, cut the frame cut in half
at the seat tube where both the main tube and down tube were
connected (Photo 3). Cut the tubing as close as possible to the
seat tube, then grind any remaining metal from the seat tube.
Photo 3 - The frame is cut in half.
Modification of the frame
simply involves turning the front half upside down as show in
Photo 4. Because the down tube (now the top tube) is shorter
than the top tube (now the down tube), this places the head tube
farther down, or the bottom bracket higher, depending on how you
look at it. Basically, now the pedals have enough
This frame modification also adds more rake because the head
tube angle is pushed forward. This will add a nice look to the
Photo 4 - Inversion of the front frame half.
Here is the newly rejoined
frame, with the front half turned upside down and re-welded
(Photo 5). If you didn't look closely, you may not even notice
how different the new frame is compared to the original, although
the new head tube position and angle would make an almost
impossible bike if the larger front wheel were to be used. Also,
the top tube is larger in diameter than the down tube - another
thing you normally don't see on "non-freak" bikes.
Yes, the front forks are already painted! Since there were
us working on this chopper, things progressed at an alarming rate.
Photo 5 - The frame is rejoined, upside down.
Originally, the plan was
to weld the screen from an old satellite dish into the frame
triangles in order to give the bike a cool "filled in
look", but unfortunately, the satellite mesh was aluminum.
Welding thin aluminum to mild steel is not something that a simple
AC welder can do, although I gave it a shot anyhow - oops. The
mesh quickly turned into toxic vapor as the welding arc blew it away.
Enzo, being the creative genius that he is, came up with the
idea of welding the original rusty chain into the frame instead, since it would
have to be replaced anyhow due to mega-rust (Photo 6). In the
end, it looks pretty cool, almost military-like.
Photo 6 - Don't toss
away that rusty chain
Finding a decent banana
seat in a few hours around here was impossible, so Enzo came back
with this humungous seat from what was probably an exercise rowing machine
(Photo 7). Although the freaky dude at the pawn shop charged him
$20 for the thing the rest of the bike was free. This thing was just plain sick. This seat
is at least
twice as wide as a regular bicycle seat and three times as long.
Photo 7 - One extremely wide seat.
To accommodate the new
mega seat, a pair of chain stays were cut from one of the many
bent and twisted frames in my scrap pile (Photo 8). The idea was
to weld the stays to the metal bit under the fat seat and then
weld the other end to the rear dropouts on the chopper frame. Just
about any old tubing would have worked, but these were handy at
Photo 8 - Butchered chain stays from an old frame.
With the new seat support
welded to the frame (Photo 9), it would be easy to just bolt the
rowing machine seat back onto the bike. Another solution that
would work involves cutting the original seat stays from the
chopper frame, move them backwards and then weld a small tube from the
top of the seat tube back to them. We wanted this chop done
that same afternoon, so this method worked just fine.
Because the seat was an after thought from our inability to
scrounge a banana seat, the frame was already painted when I did
the welding. Oh well, paint is cheap.
Photo 9 - The seat support made from chain stays