Pix and Procs
I did this mod using a drill press, a Dremel tool, hand tools and my highly calibrated eyeballs. You machinist with your fancy lathes will probably get a few chuckles.
Drill out the gear: I started by making a jig to hold the gear while I drilled it out. This made things easier and safer. With a ¾” spade bit in the drill press (DP), drill a hole in a piece of scrap wood the depth of the teeth on the gear. Switch to the 6mm bit and drill the center of the hole through. Clamp the jig to the bed of the DP. Remove the set screw from the collar of the gear with an Allen wrench. Place the gear in the jig, collar up, and grab the collar with a small pair of locking pliers to keep it from spinning. Drill out the center hole to 6mm, cutting oil is good but not mandatory as you aren’t removing much material.
Remove the axle from the truck: You Shay veterans probably know this step and can skip ahead. I placed the loco upside down in its original packaging foam to cradle it. Remove the 6 screws from the motor cover. Backing off the contacts is a pain but best to done to prevent loss of the ball bearing. Remove the tabs with the wires (1) and spread them out to the side. Remove the 2 small tabs (2). Pry the spring shims (3) up and out. Pull the pressure springs (4) in toward the center of the truck. I placed a small rare earth magnet on the springs to keep the ball ‘attached’ to the end (5). Gently pry the axle up and out.
Strip the axle: Remove the small screw and washer from the center of each wheel. Remove the wheels. Remove the plastic spacer behind the wheel. You will need to press off the bearing on the gear end of the axle and the gear (if it is still there). If you have a bearing puller, I hate you. I used the drill press. Put a 6mm open end wrench around the axle next to the gear. Put the other end of the axle through the hole in the DP bed. Press down on the end of the axle with the chuck until the bearing and gear pop off. You can leave the other bearing on.
Remove the knurling from the axle: Chuck the non-gear end of the axle in the DP. Turn on the DP and run a flat file up and down the axle until the new steel gear will slide smoothly all the way on. Avoid the very end of the axle where the wheel and bearing mount, it is already 5mm and sized to fit them.
Notch the axle for the set screw: Align the steel gear to its approximate position on the axle. With a sharpie, mark the set screw hole on the axle. Remove gear. Using a Dremel with a bur grinding bit, make a flat spot at the mark on the axle. NOTE: It is very important that the notch is deep enough so the set screw does not protrude above the collar of the gear. If it does protrude, it will hit the worm gear on the motor when re-assembled (ask me how I know). Put the set screw back in the gear, tighten it on the axle, and use you sense of touch to check it is flush.
Re-assemble the axle: Leave the gear loose on the axle. Press the bearing back on the axle. I used the DP once again by placing the non-gear end of the axle on the bed, opening the chuck so the axle will go in but the bearing won’t, and Press the bearing on with the chuck. Position the gear and tighten the set screw. For positioning, compare it to the axle that still had a gear but if you don’t have one, space it about 1mm off bearing using the calibrated eyeball method. Install the plastic spacer, wheel, washer and screw on each end (the wheel with the gear goes on the end with the new steel gear on rear truck, opposite for front). Double check that the bearings spin smoothly, I damaged one of mine with the pressing on/off. They are cheap and readily available so replace any that aren’t silky smooth.
Do the other axle: Rinse, repeat. While the truck is apart you may as well upgrade both axles. I found another broken gear and a cracked one.
Test for binding and clearance: I did a quick test to be sure they ran smooth. Snap the axles back in the truck. Using jumper leads, run power from an old track power pack to the two wires that were un-clipped from the contacts. Check for binding. If you hear a ticking you probably did not get the set screw notch deep enough and it is impacting the worm gear. If it is quiet and smooth, grease it up.
Re-assemble the Contacts: Just do the dis-assemble in reverse. Those little clips are gonna be a booger especially for old eyes and shaky hands.
Close up the trucks and test: Put the cover on and carefully tighten the 6 screws. Do another run test by touching the jumper leads from the Power Pack to the wheels or use your fancy run in station. Listen closely for any ticking that would indicate you have clearance issues with the set screw that will ruin your day.
