After a complete teardown and a quick clean of the frame I was ready to get serious about coming up with a design for the rear end.
I had to make decisions about what I could keep and what had to go. My goal from the start of the project is to keep as much of the original 3 wheeler as possible. I figure there is no reason to redesign and fabricate anything extra, beyond what I was forced to do.
I know I had to get rid of the rounded rear end frame section and the angle brace from the main frame since they occupied space the rear wheel would eventually go. Two questions I had were: What to do at the bottom of the main frame, and if I could keep the horizontal seat frame rails. Since I knew everything below the seat rails had to go, I strarted by cutting that out. From then on there was no going back, the next time this thing rolled around, it was going to be a 2 wheeled mini-bike. (maxi-bike?)
Now the fun begins. This is the part of the project that I am looking forward to the most. The design and building of the rear end. I enjoy the feeling of creativity and engineering that goes into coming up with a design idea and seeing if it pans out. I determined, by doing a few positional mock-ups, that I could keep the horizontal seat rails. This will allow me to perhaps keep the stock exhaust and the stock seat, though both may require some modification. In place, the rails still allowed enough clearance for the wheel to fit beneath. I wanted the rails to be nearly horizontal, but rise slightly from front to back.
The next major decision is how far back to put the rear wheel. Too far forward and I will run out of room for the jack shaft, brake mounting points and any other goodies that need to be crammed into the small space in front of the rear wheel. Too far back and the feel of the bike might be ruined and it would make it less nimble. After looking at a few options, I have decided to put about 3 inches between the front of the rear wheel and the main frame. This moves the rear wheel back about 2 inches from where it was as a three wheeler. I accept that I may have to adjust this as I start to work through this design, but that will be my starting point. With the seat in place, the mock up looks like the picture below.
The plastic piece with '125' on it in the picture above is a stand-in for where the gas tank will go. Now that the rear wheel occupies space previously taken up by the gas tank, the air box, the brakes and the gear sprocket, I am going to have to get creative in relocating those items. The new location of the gas tank will take the place of the odometer and choke lever, but I don't need an odometer and the choke lever can easily be re-positioned so that's not a deal breaker.
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| stripped down frame |
I had to make decisions about what I could keep and what had to go. My goal from the start of the project is to keep as much of the original 3 wheeler as possible. I figure there is no reason to redesign and fabricate anything extra, beyond what I was forced to do.
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| rear end frame |
I know I had to get rid of the rounded rear end frame section and the angle brace from the main frame since they occupied space the rear wheel would eventually go. Two questions I had were: What to do at the bottom of the main frame, and if I could keep the horizontal seat frame rails. Since I knew everything below the seat rails had to go, I strarted by cutting that out. From then on there was no going back, the next time this thing rolled around, it was going to be a 2 wheeled mini-bike. (maxi-bike?)
Now the fun begins. This is the part of the project that I am looking forward to the most. The design and building of the rear end. I enjoy the feeling of creativity and engineering that goes into coming up with a design idea and seeing if it pans out. I determined, by doing a few positional mock-ups, that I could keep the horizontal seat rails. This will allow me to perhaps keep the stock exhaust and the stock seat, though both may require some modification. In place, the rails still allowed enough clearance for the wheel to fit beneath. I wanted the rails to be nearly horizontal, but rise slightly from front to back.
The next major decision is how far back to put the rear wheel. Too far forward and I will run out of room for the jack shaft, brake mounting points and any other goodies that need to be crammed into the small space in front of the rear wheel. Too far back and the feel of the bike might be ruined and it would make it less nimble. After looking at a few options, I have decided to put about 3 inches between the front of the rear wheel and the main frame. This moves the rear wheel back about 2 inches from where it was as a three wheeler. I accept that I may have to adjust this as I start to work through this design, but that will be my starting point. With the seat in place, the mock up looks like the picture below.
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| positional mock-up |
The plastic piece with '125' on it in the picture above is a stand-in for where the gas tank will go. Now that the rear wheel occupies space previously taken up by the gas tank, the air box, the brakes and the gear sprocket, I am going to have to get creative in relocating those items. The new location of the gas tank will take the place of the odometer and choke lever, but I don't need an odometer and the choke lever can easily be re-positioned so that's not a deal breaker.
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| position of the rear wheel |
The design of the new rear frame seems pretty cut and dry, at least for now. I plan on either widening the lower mount point (yellow arrow in picture below) or bending the lower arms around the wheel if possible. Bending the pieces is more difficult but would result in a better looking result.
In the first picture below, the red lines would be frame and the light blue line would be the drive shaft.
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| side view with possible future frame locations |
The top view shows how the lower frame arms would attach at the lower pickup point and bend out around the tire to the rear drive shaft. The orange lines are the support tubing from the horizontal seat rails. The amount of bend will depend on how much room the chain sprocket, brakes and bearing take up. I want to keep enough room to allow for slightly fatter tires and mud/snow build up.
One challenge I will face is that I don't own a tubing bender and don't really want to buy one for this project. I may use a conduit bender and electrical conduit during the mock-up process and then once I settle on a design, I will pay a machine shop to bend the final tubing. My plan is to use 1" tubing for the support tubing. that is what the rear frame of the 3wheeler was built with so without doing the calculations, I feel confident it will be strong enough, provided I design it properly.
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