AHM HO Engine Motor and Worm Gear Replacement

In the bygone era of HO model railroading, a company called AHM made a variety of “yard switcher” locomotives.  You can find these all day long on eBay as “broken” usually because the motors are bad (or missing), but the rest of the engine is intact.

I created a motor mounting bracket and worm gear set so that if you purchase or own one of these, you can completely replace the motor with a much more modern one for very little money, and get you engine back into service.  This is a very simple (and cheap) replacement and all you need is a few printed pieces, a couple of screws, and the motor.

Materials needed:

(1) 6000 RPM, 12V “mini motor” (these are about $8.50 for 3 motors). They look similar to your typical speed 130 motors except that they are high torque, run on 12V and work very well for HO engines at a budge price.  The vendor from Amazon I purchased them was “YXQ” and the listing was titled: “YXQ DC 3-12V 6000RPM Electric Mini Motor High Torque for DIY Toys, 2mm Shaft,3Pcs”, just in case this link does not work. (https://www.amazon.com/dp/B0747M9HG6?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_3&th=1)

(2) M2 x 8 button head screws

(3) printed parts out of PETG (not PLA) so they do not melt.

Print:

Print the parts out of PETG. If you use PLA, it will only work for a short time.  The parts consist of a base (which will fit into the engine, a motor mount, and a new worm gear which will press fit onto the new motor.

Note:  The worm gear is loaded in it's own print profile so that I could set the global settings for it seperate from the other items you need. That is where you will find the worm gear.

The steps for the build are simple:

Chassis Preparation:

Remove the old engine components so you just have the stripped-down chassis and the power pickups. 

Motor Sub-Assembly:

Set the base plate filler in place in the original chassis.

Slide the new motor into the motor mount.  The motor copper brush power connections will slide between the motor mount’s “V” notches.  

After you slide the motor all the way in, you can bend the connections away from the motor mount so you can easily soldier to them when you go to connect the wires.

Once the motor has been slide all the way into place, install the worm gear. The easiest way to do this is to place the motor as show and start the gear onto the end of the shaft.  Then either push it on the rest of the way (you can use a small block of wood) or turn the entire assembly over and push it on a hard surface to make the gear go on the rest of the way. No adhesive is required.  The switcher engine does not have a lot of pulling capacity being a “light weight” so the gear will stay fixed in place.

Underbody Mounting:

Set the motor assembly in place on top of the filler plate so that the holes line up and then thread the M2 x 8 button head screws in from under the chassis. They will easily thread into the motor mount to hold it in place. It only has to be snug.

As you screw them in you may have to move each of the power pickups to the side to allow the screws to be tightened down.

With the motor now in place, you can connect the power leads.  The photos show a noise suppression capacitor, but this is not required unless you run into problems with your headlight.

Wires and clearance:

The space between the chassis and cover of the engine is pretty tight in the Conrail switcher, so you will want to route the wires this way, on each side of the new motor mount. A piece of tape will help when you put the cover back on keeping both wires where you need them so that the first cover goes on correctly.

Now you can place the engine weights back in place and then install the top cover.