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:
- it did not provide good slow speed performance
- it was often the source of noise
- a Sagami can motor
- NWSL universal joints
The parts you will need for this remotoring project include:
- one Rivarossi Big Boy
- one Sagami can motor (#282419 -- 28mm dia. x 24mm length, see NWSL Catalog)
- one NWSL universal joint (#4886)
- one piece of NWSL 2mm axle stock (#20204) (or equivalent)
Background
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.