Remotoring AHM/Rivarossi Big Boy
As shown in Lutz's 4-4-0 thread, I recently purchased an old AHM/Rivarossi Big Boy. It had sat on a shelf for several years, so the first thing I did was clean and lube it. It ran, but the square 3 pole motor was quite noisy and rough, so I decided to remotor the locomotive.


I Googled some threads on remotoring and [url][/url], so I went ahead and cut the frame down, modified the drive shaft, and installed a Canon DN22 motor I found on eBay. The motor is quiet, the locomotive runs smooth, but it's very s-l-o-w. I had looked at specs [url][/url] from Canon, so I thought it would be ok, but I suspect the motor I got is a 24v motor, not a 12v motor, as it seems to be running at about half speed with the throttle all the way up.

I used a scale speed indicator, and it seems to top out at 38 MPH. My layout doesn't have grades, but I tried to pull 12 freight cars around the layout and it could barely do that, plus I ran it on my friend's layout last night and it nearly stopped going uphill a few times running light.

I'm trying to pick a better motor (without going broke), so I'm looking at a Canon EN22 and a Mabuchi FK-280. Any advice? Also do these locos pull very well with a new motor? Do I need to add weight, too?

one of the issues with old Rivarossi locos are their speedy gears.
It is just as you try to drove a fully loaded car equipped with manual transmission a very steep grade uphill in the highest gear. That does not work, you have to shift down to tackle the job or you will get stuck on the grade. So it is with the Rivarossi locos when the traction tires have still enough grip. Other case is when the traction tires are old an hardened, then the wheels will spun out. In both cases the loco will fail to pull the train uphill.
Your Big Boy is one of the older examples with the motor placed into the cab. From there a drive shaft will go to the first worm gear inside the boiler above the rear group of drivers and the to the second one above the first group of drivers. From this worm gear boxes there are vertical shafts leading to two more axle worm gear boxes each one inside the frames of rear and front engines.
You have in sum 4 gearboxes with an considerable demand of power and torque this is multiplicated by the low gar ratios.
In other words you have to install relatively huge motor with a lots of power and torque output. But this motor are of seizes which will not fit into the cab.

[Image: dsc012016fotm.jpg]
Not a Big Boy, but an other Rivarossi loco (B&O 2-10-2) and just the same gearboxes and ratio.
The photo shows in the middle right the gearbox inside the boiler. The one with the steel worm an brass gear is the original ratio of 1:11 and the old Rivarossi gears have a inappropiate friction factor too. In connection with the axle gearboxes with a ratio of 1:2 you have a overall ratio of 1:22.

In sum:
- low gear ratio -> speedy loco, needs power from the motor to pull
- disadvantageous friction factors -> needs more power from the motor, this extra power is completey devastated by internal friction
- a multiplication factor of 4 sepatarte gears
=> nearly all the power of the motor is consumed by the gears

In this 2-10-2 i replaced the original gears with Roco parts and got a ratio of 1:24 and in overall a gear ratio of 1:48. After that the running behavior of the loco has changed. Before it was not so fast, because Bernd (aka modelsof1900) has installed a slowly running but powerful motor to avoid hassle with the original Rivarossi motor and speeding. Also he filled the interior with heavy type metal.
At least i fitted a relative small Maxon coreless coil motor which left space for an boiler backhead too. The demand of amperes dropped dramatically after this conversion. In combination of new traction tires this loco now pulls out the hell.
That was at least done by changing the gear ratio.

And that is a way i recommend to you to change the gear ratios in the two gearboxes inside the boiler. Why, that i have described above.
Here i used gear with an module of 0.4, a one start worm and a spurgear with 24 teeth, both press fit onto 2mm shafts.

Also an posibility is to use NWSL gearboxes (1:28 type), there are also ones for 2mm axle diameter.

The option with change motor needs a very, very powerful motor. Look for one with the biggest power output you can purchase and will squeeze fit into the cab.

Cheers Lutz
Cheers Lutz
Thanks for the advice, Lutz. Unfortunately, I don't have any gears handy, but I did find an inexpensive Canon EN-22 on eBay:

It's the 5-pole version of the DN-22 (3-pole), same size and body. I replaced the motor and that solved the problem. I found some information that ohming out the windings will let one know if it is a 24v or 12v motor. The DN-22 windings are about 60 ohms; hence, the DN-22 I had is a 24v motor, so caveat emptor when buying motors on eBay.


The Big Boy ran well on my layout, pulling all the cars I had available, and handled the grades on my friend's layout with ease. I'm going to have to tweak the decoder settings to get it run more to my liking, slow and steady. For a 40-year-old, $30 Shelf Queen, it runs pretty well. I don't need a Big Boy and it doesn't really fit my layout, but I've always wanted one, if that makes any sense, so this was a an inexpensive way to scratch that itch.
I did this once long ago, but I put in two motors, one for each engine,...and internal to the boiler, not in the cab.

I just can't find my photos,...likely before In ever got a digital camera

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