Model Railroading > Need a tip from an experienced loco repair pro

Hi all! I could use a little help from the mechanically enclined TO members.
I'm trying to install a new "male universal" bushing to the axle of an N scale Atlas loco motor. Specifically an SD9 from the "Atlas Classic" line.
I'm pretty good with tiny parts, and I don't really have any fear tearing stuff apart, but I haven't done a whole lot of "brain-surgery" style repairs yet on these new(er) type locos.
Although the concept is the same with any scale or situation where you're trying to press an item onto an axle.
Obviously it has to be a tight fit so the bushing doesn't spin on the axle. But I'm not sure what the correct technique or even tool would be to accomplish this.
As I press down with the butt end of a tweezer, I'm afraid I'll crack it or distort the shape which would render it usless.
I've attached a portion of the exploded diagram to help illustrate what the part is.
What also complicates matters is that the end of the axle is INSIDE the flywheel. So there's not a lot of room to work with.
If anyone has any experience with these or similar, I would appreciate some tips, hints and/or suggestions as to the best way manage this.
Thanks much in advance.
 

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I guess I'm having trouble understanding what your trying to do. Are you attempting to install the male universal fitting?