The home we just bought has crank doorbells in two of the doors. The cranks work, and the bell "clicks" but it doesn't "ring." I unscrewed the covers and it appears to me that the striking mechanisms are missing. there is a piece that moves when you turn the handle, but I can't see anything that would bang against the door.
The bells say "patented Dec 31, 1867." on the front.
I've sold numerous old homes with those crank doorbells (real estate broker). People salvage them, and you may be able to find replacements at a home salvage yard. Check the Yellow Pages in your area.