The Isle of Man's historic Great Laxey Wheel will be turning again by April 2020, Manx National Heritage (MNH) has said.
The Victorian wheel, which dates back to 1854, was stopped in August after structural damage was found during a routine maintenance check.
A replacement timber rod would need to be imported to the island, MNH director Edmund Southworth said.
The group estimates the repair work would cost between £30,000 and £50,000.
Tests are now being carried out to measure the amount of water needed for the wheel to turn without the full mechanism running, to "make sure it is completely safe".
Mr Southworth said specialist seasoned timber of the size needed was difficult to find and "incredibly expensive".
The cost of the project would lead to some of MNH's normal winter work programmes being put on hold, he added.
Known as the Lady Isabella, the wheel was built to pump water out of the Laxey lead and zinc mines.
The structure, which offers visitors panoramic views across the Laxey Valley, has been run as a heritage attraction since 1989.