Since this incredibly large and incredibly powerful cargo is much wider than an average fuselage, few planes can actually transport a GE90, and finding a cargo transport Antonov takes a little while.
Making things even more difficult, the 777 was too large for the hanger available, and they had no tools for replacing the worlds largest jet engine. Plus, it was only 40 degrees F below zero. Oh, and night lasts 19 hours long.
So, a few tiny problems to over come, all because one really big engine has a failure
Read the whole story at http://www.popularmechanics.com/flight/airlines/a25590/changing-worlds-largest-engine/