Rusty, To give any estimate of value of a large bell, the first thing needed is whether the bell is bronze or iron. If you don’t know, a magnet will tell you. It will stick to iron, but not to bronze. Bronze bells are much more valuable.
Second, how complete is the bell. Does it have a yoke on top, 2 “A” frame stands, and a clapper? Is there any damage (cracks, repairs, chipped edge of the bell). A photo would also help. You said it has no inscription, which would indicate an iron bell, although I do have one large bronze bell with no inscription.
Any additional information will help. Just having the diameter is kind of like telling someone the length of a car and trying to get the value. I’ll try to help, but I need more information. — Neil