I have several Athearn SD40-2’s from the mid-1980’s. I really like them but I think the motors need to be replaced with something better. I’ve never done this before, so I’m listening for the voice of experience. What motor would you guys recommend for this application and how difficult a job is it?
I would use the Northwest short line kit.You will have to mill the frame for the motor to fit properly.You will have to hardwire everything which will have to be soldered.I would also get the NWSL shaft kit to replace the noisy Athearn shafts.All in all not a bad job.You will need a rotary tool to do the milling.A line also makes a kit to replace the athearn motor.Dan
Or, you could just use a newer Athearn motor. They’re better now. 
In Oz we use the Athearn SD40-2 chassis to repower some of the local locos, without problems…
Allan Lees
On all my repowering of Athearns, I have always used a craddle to lift the can motor. I don’t understand why milling is needed? Is it the type motor Northwest Shortline uses? I have generally used the A-Line/ Proto Power West or if not kit, Mashima or Sugami w/ the A-Line universal drive assort. to adapt driveshafts. I found that after motor positioning, automotive RTV black silicone is great for motor fastening as a flexable motor mount and isolator.
Bob K.
There used to be “Helix Humper” replacement motors for Athearn engines. I wonder if they are still around. I recall the name because it wasn’t indicative of what the product was or did.
Bob Boudreau
PPW has a complete ‘drop in’ chassis as well as a remotoring kit and cradle.
My experience is the PPW pruduct is superor in smoothness with less current draw to both my 'Helix Humper’s.
ATHEARN’s newer motor’s may be an “improvement” over the old, but still not in the same league as MASHIMA.
Thanks to you all for your replies; I really appreciate the help. I went to the A-Line website & their repowering kit sounds like what I’m looking for.