My wife loves her pink bicycle, but when her bell stopped working after one to many over emphatic "bring-brings," she was anything but happy. To be more clear, the internal mechanism that caused the actuator to return after it was pressed broke. So to use the bell, she had to manually move it forward and back.
Eventually, I decided to open the bell to see how it works and hopefully fix it. While my solution may not work for the entire life of the bell, it is very simple and should provide plenty more "bring-brings" until I have to work on it again.
Step 1: Things You Will Need
A broken bell to fix, obviously.
A small, strong, rubber band.
A pair of pliers to help with dissassembly.
Step 2: Opening the Bell
These common bells are topped with a metal bowl. It can be easily removed by twisting it counterclockwise. With the top off, the inner parts of the bell are revealed. The broken part should be seen right away...
Step 3: Internal Mechanisms
Once the top is off, the small nut can be removed. A pair of pliers may be needed for this. Under this nut is a plastic piece loosely holding two washers. When the bell actuator is depressed, these washers rapidly revolve around the center of the bell. The "bring-bring" sounds are created by the washers hitting the inner sides of the bell top.
There is a step up gear ratio in use here. As the actuator moves, it turns a gear with few teeth multiple times. In turn, this gear turns the removed piece holding the washers. Thus, a little movement of the actuator causes a lot of movement with the washer piece.
The actuator should be pulled back to its starting position automatically. This is done by a pair of plastic arms connected to the actuator and a small ring placed in the center of the bell. After a lot of use, these plastic arms eventually broke away from the actuator, causing the "spring" action to no longer work.
I don't know of anyway to fix this piece that will not break again soon after.
Step 4: A Quick Fix
Since the plastic spring cannot be fixed (reliably), rubber bands can be used instead. To start, loop the rubber band through the actuator slot and pull it through itself. This is a common technique called a "rubber band knot."
Step 5: Adding Tension
The small ring with the broken plastic arms will not be used in this fix, but it might be worth keeping in case a better solution is ever though of.
This part may be a bit different for you, depending on how big of a runner band you are using. Essentially, we want a lot of tension on the rubber band when the actuator is pressed. To create this tension, stretch the rubber band around the gear pegs in the bell. For even more tension, I pulled the loop part of the knot itself around the center post as well.
With the rubber band wound, place the actuator back on its pivot peg with the slot over the center post. The rubber band will pull the actuator up against the center post. Test this a few times to see if the band pulls the actuator back in place. You may need to wrap it around the posts another time.
With that in place, carefully put the gears back in place. The small toothed gear goes on the right peg first. Then the piece holding the washers goes on the center peg. Finally, the nut can be put back on top to hold it all down.
Step 6: Test it Out
Finally, the bell top can be screwed back on to the center post. The bell will not make noise until this top is put back in place.
Obviously, the rubber band will eventually break, but this quick fix has lasted for a few weeks now on my wife's bike and sure beats buying another bell. When the rubber band does break, it can easily be replaced in the same manner it was originally put in place. Maybe some day, I will come up with a more permanent solution...