What does line-reamed mean??? - Classic Toy Trains Magazine

I working on rebuilding a 6466W tender. The whistle was chattering loudly even after cleaning and oiling. I'm thinking of replacing the brass bushing/bearing in the motor frame casting. However, the service manual recommends not replacing the bushing because its line-reamed with the casting and brush plate. It seems to imply that a jig and a reamer is required to replace the bushing.

Any help or suggests would be appreciated.