This page describes how I converted this engine from the American Flyer-compatible wheels and couplers to scale ones. The S-Helper Service box comes complete with both the scale couplers and the scale wheels. Nothing extra is needed. The tools required for this project are a set of small, jewelers screwdrivers, curved tweezers, and perhaps a magnifying visor.

The underside of the truck has four screws that need to be removed to remove the AF coupler.

The removed parts, including the screws, are no longer needed for this project (the manual suggests that the screws are needed later, but they are not).

The first step is to upgrade the wheels. From an e-mail reply from Don Thompson of S-Helper Service, this is the method I used to snap the plastic cover off of the metal gear box. I inserted a pair of curved tweezers in between the plastic cover and the wheels' axle. I then used the axle as leverage to push out the plastic cover.

With a bit of effort and careful positioning, the plastic cover snaps off of the metal gear box.

The plastic cover can then be easily removed.

At this point the wheels and gear box are fully exposed. The wheels come out easily just by lifting them up straight.

Before inserting the new wheels, I widened the wheel wipers. The old wheels are closer together than the new ones and so the wipers won't necessarily make contact (I found that out the hard way). I really bent them out a ways.

Inserting the new wheel (on the left) isn't difficult, but it does require a bit of patience and persistence. The bronze bearings have to fall into their slots on the metal gear box. Do one at a time.

I used the curved tweezers to line one of them with the slot in the gear box and then pressed it partially into place. You must also pay attention to the wheel wiper. I then did the other side.

When both were in position, I pressed the whole wheel down. You can see the difference in the scale wheels (left) and the Hi-rail wheels (right) quite clearly in this photo.

I then did the same thing with the other wheel.

We are done with this truck, so replace the plastic cover. I first slide it onto the back tab of the truck.

Next, with one hand I grab the engine's body and with my other hand I pushed down on the plastic cover to get it into position. It requires a bit of force. I found that it doesn't snap fully in place. I then used a screwdriver to really snap the plastic under the tab.

To upgrade to the scale couplers, the instruction manual tells to you use the screws that held the AF couplers in place, but those turned out to be too short. When I looked around the SHS box I found a little bag with longer screws in it. I used those and they worked great.

Once the AF couplers are out of the way, you can clearly see the three mounting holes for the SHS (or Kadee) coupler.

It is then just a simple matter of installing three of the longer screws. Make sure to not tighten the center one too much or else the coupler will not return back to its normal center position.

Once installed, the coupler sits at the correct height.

Now that I know how to do one of these, it is pretty straight-forward. The instruction manual is a bit misleading (perhaps outdated). I hope that this page with the photos is helpful to others who still want to apply these changes.

Update
My current standard coupler is the Proto Max couplers. I replaced the above-mentioned couplers with these couplers. However, when I set the engine up on my Coupler Gauge, I discovered the couplers were about 0.060" too high.

Using several styrene thicknesses, an NWSL Chopper, and Testor's styrene glue, I made a shim that perfectly matched the difference between the tops of the gauge and coupler. I painted the shim with Floquil's "Grimy Black", which seems to the match the underside of the engine just about right.

This next photos shows the coupler installed. I also used a washer to keep the screw from crushing through the draft box. I completed the work by painting the washer with Floquil's "Grimy Black". The coupler is now at the perfect location and matches the couplers on my cars.