John

Welcome to the forum!  As my layout is built for operation with multiple operators of differing skill levels handling my trains, Athearn Blue Box locos are my "go to" choice, especially when I can pick them up used so cheaply at train shows and on-line.  As your other thread inquires about rebuilding a Blue Box loco, I thought I'd respond to both threads together.

The first thing I do is completely dissassemble each loco to clean out dirt, crud and dried up grease.  I reassemble the trucks and oil the gears with a couple of drops of plastic compatible oil (it doesn't take much).  I next solder a couple of 3 to 4" lengths of 28 or 30 gauge flexible stranded wire to the steel electrical contacts on each truck so that the loco does not have to rely on contact with the chassis or the steel contact strips along the top of the original motor.  

I like to remotor these locos using the SMC FP280-KN DC 16v 11200 rpm can motor currently available on-line for $3.25 each.  Don't let the cheap price fool you!  These are strong, torquey motors that will smoothly propel a BB loco all day at prototypical speeds without a hitch, all while drawing significantly less current than the original motor.  Note that these motors were originally designed to power automotive side view mirrors.  Because such mirrors are often in near proximity to stereo speakers in the car door, these motors come with an interference shield to keep motor noise out of the speakers.  If the motor will fit inside your loco with the shield in place, great.  However, the actual motor is significantly smaller with the shield removed, especially useful when installing one in a GP9.  The shield can easily be removed with a razor saw or hack saw.  These motors can easily be attached to the chassis using hot glue, silicone glue, double sided foam tape or whatever you prefer.  Just try to mount the motor shaft in line with the gear towers on the trucks.  I use lengths of 1/8" styrene tubing to adapt the original Blue Box flywheels to the 2mm shafts of the new can motor. That way, the only part of the original BB driveline that changes is the motor.

I don't know whether your are going to convert your Blue Box loco to DCC.  I would highly recommend doing so as DCC allows you to run your trains instead of the track, and most of the features you are looking for are included on even basic non-sound decoders.  If I'm not installing sound, I like to use the NCE D13J decoder and one of my DIY keep-alive circuits.  This arrangement gives me a smooth and quiet running loco that will crawl along at super slow speeds with no hesitation or stopping on dirty track and all the lighting functions I desire.

To mount the decoder and keep-alive circuit, I first glue or use double sided foam tape to attach a long 1/2" wide strip of .080" styrene to the top of the new motor.  The length of this styrene strip should be cut to allow it to fit just inside the headlight lenses on each end of the loco.  This will allow you to mount the new headlight LED's to the ends of the styrene strip.  The styrene strip also provides a nice surface to attach the decoder, keep-alive and all associated wires and keep everything away from and clear of the drive line.  If you want them, the styrene strip also gives you a place to install an engineer and fireman.

If the shell of the Blue Box loco does not already match one of the road names I use on my layout, I will strip it using 91% alcohol and a toothbrush.  I next add any details or grabs I want, then repaint the shell into an approriate livery for my layout.  Regardless of whether I repaint the shell or buy a loco already painted in a road name I use, I like to weather my locos as, to me at least, they look more realistic and the weathering tends to hide the fact that a loco is not superdetailed.  Once the weathering is completed, I then add glazing to the cab windows.  I find it is easiest to simply glue pieces of any flat clear plastic into place using pressure sensitive adhesive (PSA) such as that available from Micro-Mark.  Trim the clear plastic pieces to fit inside the windows, apply the PSA around the window openings on the inside of the shell, allow the PSA to dry (it becomes very tacky), then press the pieces of clear plastic into place.  Unless broken, I also like to retain the original Athearn GP9 headlight lenses.  If already broken, I replace the lenses with pieces of optic fiber.

This method results in a loco that was inexpensive to buy and refurbish, is as robust as a brand new Athearn loco, looks good and operates smoothly and quietly enough to please all of my layout operators.  Best of all, if one of my operators manages to drive one of these locos off the edge of the layout, I haven't lost a $200 or $300 loco!  I hope this helps.  Good luck!

Hornblower