Dina Rudick/Globe Staff

St. Mary’s Church in Charlestown has had the same organ for 121 years thanks, in part, to Lee Eiseman.

Dina Rudick/Globe Staff

The stops on the 3,000-pipe organ.

Dina Rudick/Globe Staff

Eiseman is not Catholic — he’s a secular Jew. Still, he has spent thousands of hours volunteering to restore and keep up the organ.

Dina Rudick/Globe Staff

He came to care for the 1892 instrument because of a promise he made to the 20th century’s foremost classic organ builder and restorer, Charles B. Fisk, in 1974.

Dina Rudick/Globe Staff

Eiseman has kept it operating through thousands of weddings, funerals, and morning Masses. Now, the church is embarking on a large-scale restoration project.

Dina Rudick/Globe Staff

The six-month, $250,000 project involves disassembling, repairing, or replacing, thousands of fragile wood, metal, leather, and fabric components.