Learn Spanish (Latin America): Hacía meses que la grieta crecía.

The structure Hacía + [time] + que requires the main verb to be in the imperfect tense to show an action was already happening and ongoing in the past. While English uses "had been growing," Spanish simply uses the imperfect crecía to show the crack was still in the continuous process of growing at that specific moment in the past.

How would this sentence change if I wanted to say the crack has been growing for months up to the present day?

You would change both verbs to the present tense: Hace meses que la grieta crece. Using Hace with the present tense means the action is still happening right now, while Hacía with the imperfect means it was ongoing up to a specific point in the past.

Can I change the word order and put the time expression at the end of the sentence?

Yes, you can say La grieta crecía hacía meses. Notice that when you move the time expression to the end of the sentence, you must drop the connecting word que.

Is it normal to use crecer (to grow) for an inanimate object like a crack?

Absolutely. While we often learn crecer for plants or children growing, it is commonly used in Spanish for anything that increases in physical size, intensity, or amount. You will often see it used for rivers, problems, or in this case, una grieta (a crack or rift).