I have an extra bell attached to the doorbell that goes out to my workshop. It's the old style ringer bell. It stopped working so I checked the transformer and the wiring run and all connections. I've got it narrowed down to the bell itself. After cleaning some crud off the contacts it still isn't working. I can hear the electro magnet activate, but it seems there is a crucial gap between the contact and contact arm. With some experimenting I can get it to work, but I would be interesting to know what the gap should be. Should I see 0 ohm between them when the button is open?

Wikipedia bell diagram