Note: if this post is more than 10 minutes old, the bike probably has been modified.
This is my first motorized bike build; a steel framed Schwinn Delmar. By the time it was completed I had replaced everything on the bike, keeping only the frame, fork, and seat.
My first priority was to upgrade the brakes. I installed the front disc brake on a mount I fabricated from a piece of 3/16” x 3” steel bar. I created a jig to locate the mount properly and to hold it in place while I welded it to the fork. The front wheel was built with a Shimano XT disc hub and the brake is a mechanical caliper Avid. The rear brake is a BMX side-pull style with a 94mm reach bolted to the underside of the fender mount.
The next objective was to fit a multi speed freewheel into the frames narrow rear dropouts. I cut a rear hub from existing wheel and replaced the 6 speed freewheel with a 5 speed to narrow the hub to 120mm. I laced the hub to a Sun rim and dished it to provide the proper chainline on the engine side. To improve the gearing range, I replaced the one piece crank with an American-to-European bottom bracket adapter and a Sugino crank with a 48 tooth chainring. Now I can pedal-assist the bike up hills at close to 30 mph.
The engine is a Grubee Star-fire and is unmodified with the exception of port-matching the case to the cylinder at the transfers. The engine is mounted to the downtube with a mount made from a steel PVC pipe clamp. I made the exhaust from a Tomos moped muffler after the original fell apart on my first ride.
Miscellaneous mods: Threaded to threadless stem converter, Bontrager bar and stem, pit bike throttle, Shimano rapid fire shifer as clutch lever, Shimano bar-end front shifter converted to thumb operated rear shifter, and fabricated sprung chain tensioner.
My foundation is complete. Future plans include an expansion chamber, Dellorto SHA carb, smaller rear sprocket, and porting the cylinder.
This is my first motorized bike build; a steel framed Schwinn Delmar. By the time it was completed I had replaced everything on the bike, keeping only the frame, fork, and seat.
My first priority was to upgrade the brakes. I installed the front disc brake on a mount I fabricated from a piece of 3/16” x 3” steel bar. I created a jig to locate the mount properly and to hold it in place while I welded it to the fork. The front wheel was built with a Shimano XT disc hub and the brake is a mechanical caliper Avid. The rear brake is a BMX side-pull style with a 94mm reach bolted to the underside of the fender mount.
The next objective was to fit a multi speed freewheel into the frames narrow rear dropouts. I cut a rear hub from existing wheel and replaced the 6 speed freewheel with a 5 speed to narrow the hub to 120mm. I laced the hub to a Sun rim and dished it to provide the proper chainline on the engine side. To improve the gearing range, I replaced the one piece crank with an American-to-European bottom bracket adapter and a Sugino crank with a 48 tooth chainring. Now I can pedal-assist the bike up hills at close to 30 mph.
The engine is a Grubee Star-fire and is unmodified with the exception of port-matching the case to the cylinder at the transfers. The engine is mounted to the downtube with a mount made from a steel PVC pipe clamp. I made the exhaust from a Tomos moped muffler after the original fell apart on my first ride.
Miscellaneous mods: Threaded to threadless stem converter, Bontrager bar and stem, pit bike throttle, Shimano rapid fire shifer as clutch lever, Shimano bar-end front shifter converted to thumb operated rear shifter, and fabricated sprung chain tensioner.
My foundation is complete. Future plans include an expansion chamber, Dellorto SHA carb, smaller rear sprocket, and porting the cylinder.
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