The term "rebuilding" as concerns a diesel primemover has been used rather loosely in the railfan press. Every engine does have a prescribed regimen from its manufacturer. As for ALCo there is a full set of Maintenance Instructions (MI's) for the engine as well as Engine Maintenance Schedules for every application, i.e. stationary, marine, railroad, etc. The instruction for locomotives is MI-11273. In it are instructions to be followed daily, weekly, bi-weekly, monthly, semi-annual, annual, bi-annual, four year and eight year. Each of these directs the reader to perform specific MI's except for the eight year which says plainly: "Remove, inspect and recondition engine". I would only consider the eight year maintenance group as a rebuilding.