...hardly an Athearn but, maybe there was something to gain.
The new motor came from an online vendor. Since dual shaft motors can be expensive, I had to take a chance when I found these for around $7.50 each, including shipping. They were a drop in fit for the Bachmann and AHM all wheel drive diesel models, but the shaft is too small for an Athearn...a good thing as I found later.
The only modification required for the Bachmann was a simple bend on each of the posts to clear the frame. Once the leads were soldered on, it was a simple matter to place a small blob of silicone adhesive caulk to the frame, nestle the motor into place...making sure all remains properly aligned while setting.
You can see in this side-by-side that the motor truly is a drop in fit, being about 10% heftier in the field magnet and case but well within tolerances for clearing the body shell...
An honest evaluation would include increased pulling power, it is a beast compared to its former self. It also runs much slower at the top end of the throttle, both great qualities that I figure comes from the new motor's beefier measurements over a stock buzzer.
Sadly, it does not have very good slow running qualities, not even for a road unit, dashing any hopes of mass re-motorings of the fleet on a budget. The original motor runs much quieter and has better low end throttle control---unless it's burnt out like this one was, of course. Because the new motor is also a good bit louder, that leaves it relegated to the holiday tree lapping fleet for the most part...a good thing since these locomotives tend to chew through motors about ever three years under those conditions anyway.
In the end, it's not bad for seven bucks, just save you peanuts up for one of the better can motors when you want a whisper quiet tie crawler. However, this one is more than worth it for rescuing the family Christmas gear grinder, and will last for many holidays into the future.