Looking at the video of 425, and seeing the bell on our own #12 perform amazing feats of acrobatics, I can't help feeling that they are not supposed to do that. What are the possible causes of the 360 degree rotation of a locomotive bell, and how if need be can this be remedied?

On most ringers of the Gollmar design there is an governor bolt and locknut at the top of the mechanism that controls how much swing is applied. You might try backing it out a bit to see if you can stop the full rotation.

Chris Allan

Chris is right about the governor bolt. Those things are enough to make a grown man cry sometimes as about the time you think it's just right it may decide not to start ringing or it will do somersaults.
They don't take nearly as much air as you would think and a lot of times, that's the problem We had a 4 position valve on the 1522 and we would start on the third notch and back it down to 1 notch. Seemed to work, but they still have a mind of their own.
I've seen a notice from a Frisco roundhouse foreman concerning basically the same thing, so it's nothing new.

Just mount a crossbar to the top of the hanger to keep it from swinging all the way around. This was standard equipment on some roads