Well this is my first instructable so lets get started. Ever since i was very young, I have wanted a dirtbike. Only problem is that we live in a suburban area and it is not practical to drive to the local mx track. I am only 13, so I cant drive myself. This means I had to throw the idea of a consumer dirtbike out the window. I would have to make one from scrach. The power boost for me was from 1/2 horsepower to 3 horsepower
Step 1: Finding a Frame
If you dont already own a razor mx500 or 650, know that any 36v-size kids electric dirtbike will do. If you do not posses one, you will need to find one. Craigslist is a good place to look. I found mine for 40$, that included the frame and the wheels.
Step 2: Parts
If you have a full frame, and wheels that hold air, these are the main parts, you may need to buy special or alternate parts based on your own personalized build. 80cc engine kit for gas bike, 5/8 inch bearings x2, keyed shaft 5/8 inch 9 inches long, 2 5/8 inch bore sprockets, 415 chain, 5 feet, 200mm shock(optional, i bought it because it is longer that original and will give me some raise), pull start kit
Step 3: Motor Mount
The motor mount is important, it will allow the motor to mount to the frame. It is made from some scap flat stock and some 1 1/4 inch pipe i got off the end of an old electric scooter. You will need a welder for this, so use your own or ask a freind. This is the only part that needs welding. The pipes will need to be joined at and angle, so if you dont have the proper tools to do this, you will need to use this website: www.dogfeatherdesign.com on this website you enter the pipes diameter and what angle you want the cut and it will generate a paper template that you wrap around the pipe and cut along the line. The angle between pipes needs to be 70 degrees. So, one pipe needs to pe perpendicular to the flat stock, and one needs to be at a 20 degree angle in respect to the flat stock. Follow the examples of the pictures and you will end up with a motor mount that mimicks the seat post and down tube of a bicycle that the motor is designed to mount to. After you finish welding, drill 2 holes and bolt the mount to the frame.
Step 4: Bearings and Rear Brake
To add the bearings, simply line them up and bolt them to the swing arm like seen in the photo. To make the rear foot brake, cut a peice of and old bike handlebar about 4 inches long. Flaten an inch of one end. Then put the flat end in the vice and bend the pie about 40 degrees. Then drill a hole in the flat end and bolt it to the foot rest bar like seen in the picture. Then, get a brake lever and drill a hole in the end of the lever so that you can bolt a peice of scrap metal to it to form a pedal. Then run the brake line from the brake lever to the rear caliper.
Step 5: Exaust Pipe Bending
The next step is bending the exaust so it will fit the frame. The best way to do this is with a blow torch. Fit the engine and exaust on the frame and you will see where you need to bend it.Also, you will need to shorten the intake manifold on the engine. Cut it in 2 places, about one cm apart, then sand the edges flat and weld them together.
Step 6: Drive Train
To make the motor turn the wheel you need a drive train. Run chain from the motor to the sprocket on the keyed shaft. Add the key to the sprocket to keep it from moving. Then run chain from the second sprocket to the wheel. Your motor will now drive the wheel. This particular rear wheel that im using has a racheting sprocket mount, which means push-starting the motor is not an option. If this is true in you case too, you will need a pull start kit. To mount the sproket from the kit to the wheel, use a hole saw to enlarge the center hole and the drill the coresponding 4 holes and bolt it to the hub like you would normaly.
Step 7: Decoration
Im sure you will want your bike to look nice. For me that means a white paint job and blue fenders. If your are going to spray paint, you must strip the original paint off first. Plz vote for me and like, thanks. If you need help on a specific part, leave a comment and ill upade the post within 2 days with new, more helpful instructions on that part. This build was so big and long i cant remember every little step i did, only the major ones.