I had this Gary Fisher Bike Frame laying around so I though why not put it to good use and build a motorbike out of it. There were many complications with this process but I managed to push through with the designs of the motor mount and CVT front pulley modification.

Note: I will talk about the crucial steps to the best of my ability without crowding to many words onto this page

Modifications/Procedures to Complete this Project

• Machine Crankshaft from 20mm (0.787in) down to 0.75in

• Bypass 212cc Governor

• Choosing the right Carburetor and Install

• Hook Up Throttle Cable and route to proper cable length

• Switch to Iridium Sparkplugs (For a more stable spark)

• Machine rear Sprocket Squish plates

• Modify/Extend CVT Front Pulley

• Design, Machine, and Weld Motor Mount and Motor Mount Brackets

Machining Crankshaft down to 0.75in

When I was able to get the motor to my shop at SFSU,  the front pulley on the transmission would not slip over the output shaft of the motor. This meant that I would have to tear down the entire motor to get the crankshaft out, then put the crankshaft on the lathe to machine it down to 0.75in on the output shaft. Below is a picture of that process. The output shaft was machined from 0.787in to 0.75. All of this work just to cut down 37 thousandths from the output shaft. The process of removing the crankshaft was tedious. Almost everything had to come out, the Left side cover, Magneto and CDI, Right Side Panel, Flywheel, Pull Starter, Piston Lower Rod Cap, Camshaft, Pushrods, and Cam Followers. I was surprised to see that the camshaft was entirely made out of Nylon around a steel shaft but after looking back at the price of the motor, I can see why this was the choice.

(Right Image is of the Output Shaft being machined down. Left side is the all of the components and tools needed to get access and remove the crankshaft)

Designing and Machining Rear Sprocket Squish Plates

Next came time to get the 48t 420 sprocket attached to the rear wheel. There was only one issue with that, I am using a bike wheel and the style of old rim brake wheels I use don't have any sort of bolt pattern attached to the wheel. 

So I had to get inventive

I noticed that there were tapered edges on the left side of the wheel. That got me thinking about hub-centric wheels and wheel alignment. I quickly thought of having a hub-centric squish plate that would sandwich and self align on both sides of the tapered hub leaving the face of the plate to be perpendicular to the axel shaft. In one of the images you will see the sprocket mounted to the wheel from a top down perspective and hopefully you are able to see the even torque distribution and how that affects the centering of the sprocket.

Below are pictures of the Assembly Drawings and images of the Sprocket set.

Designing and Machining Front CVT Pulley extension

Another issue that was brought up was that the front pulley would not slide over the output shaft entirely because the output shaft was not long enough for the secondary centrifugal clutch pulley. This meant I had to modify the inner front pulley to have a keyway extension that would be cut on the lathe and welded into it then machined down to its final diameter of 0.75in. This was done in this order due to heat distortion of the weld that may cause the extension piece to go out of alignment with the output shaft. Below are the pictures and drawings of the entire front pulley assembly.

Designing, Machining, and Welding Motor Mount and Motor Mount Brackets

The last and final step was to design the motor mount that would secure the motor down to the frame and have the motor on the back for the ease of alignment of the final drive chain. I had to measure the position of the 10T sprocket with respect to the corner of the motor mounting plate. Once I obtained those dimensions I was able to model the rear end of the bike frame and design a motor mount that would align itself with the sprocket on the wheel. On the support legs connecting to the bottom of the frame near the rear dropout, I had cutout a slot for a tensioner pulley that would be bolted in place and allowed to 

Below I have attached images of the drawings and motor mount parts.