How to remotor a Rivarossi Big Boy

I have "remotored" several of the old "first-run" HO Rivarossi Big Boys that were produced by Rivarossi and imported by AHM back in the 1970s. The latest batch of Rivarossi steam locomotives being imported by Model Expo have been redesigned. This article does not apply to these newer locomotives and remotoring is probably not necessary. The information below should be useful to to anyone doing similar work on the older 1970s era locomotives.

The oldest Rivarossi steam locomotives were fitted with a square three pole motor. Later (but still in the 1970s), Rivarossi steam locomotives were fitted with a round three pole motor. The older, square three pole motor had several disadvantages:

I have successfully fitted an "old-style" Rivarossi Big Boy with: This article will explain how these modifications were made. It should be mentioned that the modifications will require some cutting of the Rivarossi body weight and fabrication of an "L-bracket" for the new motor. As a result, this type of work should be performed only by those of you who feel comfortable doing such things.

The parts you will need for this remotoring project include:


There is one other difference between the "old" and "new" style Rivarossi Big Boys. They use different gearing in the upper gear boxes. The old style Big Boy uses 11 tooth gears. The new style Big Boy uses 13 tooth gears. The result is the newer Big Boys are geared lower. The Big Boy I remotored had the old style higher speed gearing. As it turns out, the locomotive speed after remotoring was completely acceptable. I have not tried it with the newer (lower speed) gears, but I would guess that it too would be acceptable.

Preparing the body weight

The first and most obvious step is to completely dis-assemble the locomotive. Once dis-assembled, take the body weight and place it in a vice. You will need to cut off the old motor mount mount flush with the inner (forward) face of the mounting area as shown in Fig. 1. Burnish the cut area with a file to remove any metal fragments or flashing.

Fig. 1. Cutting the bodyweight.

Fabricating a new motor mount

The Sagami can motor I used barely fits into the cab of the Big Boy. An "L-bracket" must be made such that the new motor occupies roughly the same space that the old motor did. I used heavy duty (1/16 inch thick) pipe strapping material. First I used a drill to enlarge one of the holes in the strapping so that the front bearing of the can motor would fit through. Once this hole was big enough, I marked where the screw mounting holes needed to be to hold the motor to the bracket. I then drilled this holes and attached the can motor to the bracket to test the fit. A picture of the "L-bracket" is shown if Fig. 2.

Fig. 2. Motor mount.

When this portion of the bracket is finished, remove the motor from the bracket and partially assemble the Rivarossi body weight and the lower half of the boiler. Now, set the motor in its position noting its relationship to the top of the body weight. The pipe strapping must be bent so that the motor fits as low as possible without touching the plastic underbody. You may want to set the upper half of the boiler in place and note the close vertical fit of the motor. After bending the strapping, cut the "L-bracket" leaving about an inch for the lower portion of the "L". You will need to drill two holes in the bottom portion of the "L" which will allow size 2-56 screws to pass through. Once drilled, clean any flashing off the mount and again attach the motor to this bracket. Place the motor/bracket in position on the body weight. Mark on the body weight where the newly drilled holes are, then drill and tap the body weight so that it will accept size 2-56 screws. Now attach the motor and motor mount to the body weight with two 2-56 screws. Check the fit of this motor/bracket assembly. Place the upper half of the boiler on top of the motor to verify its fit. If any adjustments need to be made, use a small rat-tail file to elongate any of the mounting holes necessary. Re-verify the motor assembly fit with the upper half of the body shell attacked.

Modifying the Rivarossi upper gearboxes

Normally, the upper gearboxes of the Big Boy are attached directly to the body weight. This can result in some noise being transferred to the locomotive body. I found a way to reduce this noise. Additionally, the method I propose also allows you to "tune" your drive-train so that it runs optimally. Instead of placing the gearboxes directly on the body weight, I placed a small neoprene "O"-ring under each gearbox. I used an "O"-ring that fits snuggly into the indentation for each gearbox. After putting the "O"-ring in place, attach each gearbox with the original screws and snug it down lightly. Leave these screws lightly tightened. You will "fine-tune" them later.

Drive Shaft

A new drive shaft must be made to connect the 2.4mm motor shaft to the 2.0mm shaft of the rear upper gearbox. NWSL makes a universal joint kit that is perfectly suited for this. The NWSL part number is 4886. You will also need some 2mm axle stock (or .078 inch piano wire). This universal joint kit includes both a 2.4mm joint end (for the motor) and a 2.0mm joint end (for the gearbox shaft). You will have to assemble the joint ends on their respective shafts and then measure the distance between them to get the correct length for this universal shaft. When you are sure that you have the correct length, glue the universal joint ends on all shafts so that there will be no slipping.

Final Adjustments

Once the drive train is completed, it is time to test run and "fine-tune" your locomotive. To do this, your locomotive should be completely assembled less the upper body shell. Set the locomotive on blocks so that the drive wheels are not touching the work area surface. Now apply wire jumpers from a model train power supply to the motor. First, it is important to make sure that the entire drive train is functioning properly. After you have verified this it is time to do the "fine-tuning". Run the locomotive on its raised blocks at a medium to slow speed. As it is running, adjust each of the four screws (two screws per gearbox) so that the locomotive is running at the highest possible speed. You will also notice that this position of the screw will also result in the quietest operation. It will be necessary to adjust each screw several times (working your way up and down the drive train). Once you are satisfied with the adjustments, stop the locomotive and place a small amount of dry lubricant in each of the joints of the universal linkage. I used "Greasem" by Kadee. I found that this reduced the noise even more.

Final Wiring

There is not much to say about wiring. The most important thing is to make sure the motor is wired using the proper polarity (you want to make sure the locomotive moves in the same direction as others when supplied with the same polarity).


Overall, I was very pleased with the resulting performance of the remotored Big Boy. After "fine-tuning", this locomotive ran as quiet as some of my Atlas and Stewart diesels (with Kato drives). I was also concerned that the older, higher speed gears would cause this locomotive to run too fast. However, this was not the case.

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Wes Barris