It's always fun when building a chopper from a complete bicycle to keep some of the original character in the bike. Like one of the other choppers we built, Granny's Nightmare, I try to keep the theme of the original mountain bike in this chopper, The Mountain Lion.
To create a chopper rebellious to the "normality" of every day life, yet still claim to be worthy of trail riding, one will need a heavy mountain bike with front suspension. Where does one find a scrap suspension mountain bike? The city dump of course! That's where many Atomic Zombie Extreme Machines krew members find all kinds of parts for their creations. Atomic Zombie Extreme Machines
More cool projects can be found at: http://www.chopzone.com
Step 1: Find a Donor Bike and Take It Apart
All the little bits came apart nicely, and there was no damage to the frame, wheels or bearings. For this chopper, I planned to use all of the parts, so it's a good thing nothing was bent. When you hunt for donor bikes at your local landfill site, you have to get there right before closing, or the "bulldozer man" will turn all the usable bicycle salvage into twisted piles of unrecognizable scrap.
Step 2: Cut the Top and Head Tubes
I wanted to extend the suspension forks a great deal, but still keep the bike functional, so the frame would have to be extended and the rake increased, or it would become a skyscraper. Since the top tube and down tube were exactly the same diameter, I just cut the head tube and top tube from the frame, so I could re-attach it upsidedown to the down tube.
Step 3: Extend the Frame
That was easy! I just inverted the cut section of top tube and butt-welded it to the down tube to create an "extendo" frame. This modification increased the rake and handlebar-to-seat distance so that a long set of forks could be used without raising the bottom bracket to ridiculous heights. There is no real trick to welding the two frame pieces together, just try to get them as straight as possible, then grind the welded joint smooth. If you do a good job with the grinder, the tubing will look like one continuous piece when painted.
Step 4: Make a New Top Tube
Wouldn't you know, that chunk of muffler tubing over in my scrap bucket was just the right length and diameter to become the new top tube for the newly extender frame. In order to facilitate welding, and follow the design of the original bike, the tubing is hammered in a little at the ends. This is done because the tubing is much wider than the seat tubing, and it makes the welding job a lot easier. Crushing the ends in a vice also works.
Step 5: Cut Tubing to Fit
Muffler tubing is much like electrical conduit in wall thickness, slightly heavier than bicycle tubing. The tubing I found in my scrap bucket is about 1.25 inches in diameter, and seemed to be about the same diameter and thickness as the original tubing on the frame
Step 6: Weld and Grind Tube
As long as the new top tube fits, just start welding it in place. Since there isn't much that can go out of alignment, it's just a matter of getting a clean joint, and welding the tubing all the way around. This photo shows my completed and fully ground frame. On to the next step - the forks.
Step 7: Chop the Forks in Half
For this chopper to become a worthy beast, it was decided that keeping the front suspension in tact would be a good idea. The front forks were cut just below the crown in order to leave about 1-inch of tubing behind. The reason for this is because I planned on using 1 inch conduit to extend the forks, and by chance, the outer diameter of the original fork leg tubing fits perfectly into the conduit - no alignment necessary!
Step 8: Extend the Fork Legs
Extending these forks was so easy, I was starting to feel lazy! Just cut two equal lengths of conduit (I used 4 feet each), and jam them into the top of the forks, as shown in this photo.
Once they were both in place, I laid the unit on a flat surface and weld away. As long as you keep the distance between the fork legs the same all the way down, you will be home free.
Step 9: Join the Fork Bottoms
Now that the top of the forks are welded to the extension tubes, repeat the process with the lower section of the forks. Because the lower half contains the suspension, make sure to leave enough room above the moving part of the forks for travel - on these cheap mountain bikes, this is not more than 2 inches. Also, weld an inch or so at a time and let the area cool. There are plastic parts inside the sleeve used as bearing surfaces for the sliding part of the fork legs.
Step 10: Check Forks - Are They Straight?
The welded fork set should be straight as an arrow. Because the original tubing was used as a guide, there is no excuse to have a crooked or warped fork, got it?
Step 11: Install Forks and Bearings
The forks and bearing hardware are installed on the bike. I like to temporarily place the forks and wheels on a chopper in order to visualize what might come next. Some of the best ideas are spur of the moment, and if you can visualize the plan in your head, you will save a bundle on paper and pencils
Step 12: Make the Seat Frame
For the Mountain Lion, I wanted a seriously padded seat, after all, it would probably be riding over rough terrain. Of course, I didn't want a seat so huge that it looked as though I tore it from an SUV either. For this chop, I made a foam block seat using two pairs of old speed bike forks.
Step 13: Cut Seat Post Clamp to Fit
Since the homebrew seat will bolt directly to the frame, I did not want the original seat post clamp, so it was cut down as short as possible.
Step 14: Make and Install Seat Base
One of the spare fork sets will become the base of the seat. Although any small tubing would work, why not use scrap from the bicycle parts bin? The stem is cut from the forks right at the crown, then the legs are bent together by force.
To install the seat base, and allow it to be removable, a small stump of seat post tube was welded to a plate which is in turn welded across the fork legs. This will hold the back of the seat base into the original seat tube, and the front will then be bolted to the frame using the fork dropouts.
Step 15: Parts for the Seat Back
This chopper was going to have a seat with a backrest as well - when you are climbing those steep mountains, you wouldn't want to fall off the bike. The other pair of spare forks was cut up. The legs were cut from the crown on whatever angle you need to recline your seat. Don't worry about the exact angle when cutting, you can always grind the forks later to get them the way you want.
Step 16: Join the Fork Legs to Create a Seat Frame
Once the four fork legs have been welded together to create your seat frame, insert the seat post stub into the seat tube then center the dropouts to the middle of the top tube on the frame. Make a hole where the bolt will be placed on the frame in order to connect the seat to the frame.
Step 17: Bolt the Front of the Seat Frame in Place
The bolts are either welded to the frame on each side, or a long bolt is used through both holes. Once installed, the seat frame will be held solidly in place, yet be easy to remove.
Step 18: Make the Seat Pads
To try something a little different, the seat padding will be made from three small blocks. The blocks are made by gluing some 2 inch foam to a few squares of 3/4 inch plywood. Although the padding will be minimal, it still beats a typical bicycle seat which has an even smaller surface area, and almost no padding at all. "Wedgie" seats are evil!
Step 19: Staple Material Around the Padding
The seat covering is made from the highest quality vinyl material money can buy - in this case $3 worth. Because the seat blocks are square, you will have to wrap the material around as if you were wrapping a boxed gift. Stretch the material as tight as possible and staple it on two sides, then fold over the other two corners and do the same. This method is not as nice as a fully sewn seat cover, but I don't have a sewing machine in my garage, do you?
Step 20: The Completed and Mounted Seat
To complete the seat, bolt the foam pads to the forks by drilling holes and using woodscrews. Any number of pads can be positioned in whatever placement you like, just make sure the seat is at least a little bit comfortable for those long back road hauls.
Step 21: Make a Fender From Sheet Metal
The Mountain Lion has a large rear fender, cut from some scrap sheet metal of approximately 12 gauge. This photo shows the three pieces that will be welded together in order to form the fender. The two side pieces were cut from the same pattern using a jigsaw, and the center strip is wide enough for the rear tire, and long enough to wrap around the round part of the fender.
To make the center strip conform to the curve on the fender, it is first tack welded to the end, then bent along the curve, placing tack welds at about every half inch (Photo 24). Just keep tack welding and bending until the entire length is completed.
Step 22: Tack Weld the Fender Together
Once you are done tack welding and bending the center strip, it should form a perfect curve along the top of the fender. At this point it is easy to manipulate the sides to ensure the entire fender is aligned properly.
To ensure that your fender will be solid, and for that professional look, the entire length of the joint on both sides of the center strip should be welded. It's best to weld with the amperage a little low, even though the weld will be chunky because we will grind it all away anyhow. Better to do a bit of extra grinder work than to have to fill in a burn through on this part of the build.
Step 23: Completed Fender, Welded and Ground Smooth
If you have some patience, the finished fender will look factory pressed after you grind the welds. I always do the rough grinding with a heavy disc, taking the weld area almost flush with the metal, then I switch to a cut off disk for the fine work. Once the fine work is done (this includes re-welding pits and holes), I use a sander disk to clean it right up.
Welding the small missed areas and pin holes usually takes two or three attempts to get right, so have patience and you will be able to make a perfect fender. Your grinder is your best friend when doing this kind of work.
Step 24: Test Ride Your New Chopper!
The rest of the components were installed on the bike, so it could be taken for a test ride before painting. It's always a good plan to do this, as any adjustments or additions will wreak havoc on your painted frame. Don't worry about cables and shifter, just get the core components together to make sure everything fits, and nothing was left out of the design.
Step 25: Ready for the Road
Here is the completed and painted Mountain Lion chopper. The ends of the forks, head tube and rear triangle were sprayed black just like the original frame - the rest of the bike is red. Although this bike is a radical departure from the original bike, it still shares some of it's heritage - working suspension, 18 speeds, and off road capable frame. A chopper for hill lovers and mountaineers everywhere!
Step 26: On the Road Again
Overall ridability of the chopper was good, the suspension still worked over rough terrain, and the seat pads picked up the rest of the road shock - better than the original seat. The front forks felt a little loose at first, but that was only because of the front suspension having a little play side to side. The original bike suffered from this as well. Notice the cool red tail lights installed on the rear fender sides.
Step 27: Head to the Hills
Adam rips down the back lane, heading for the bike trails. If you're going to hit the back trails and venture where no "bike freak" has ventured before, then at least do it in style - do it on a chopper!
Step 28: More Projects - Bikes, Robots and Spy Gadgets