One of my favorite little diesels on the layout is the AHM SW-1. This model is very overscale for HO, probably is around 1/80 scale. Which makes it a little small and narrow in OO, but this is not very obvious on the layout, it passes for OO. The truck wheelbase is correct for OO, at least.
For about 6 years I used the original conversion I made of this model, but as with my first diesels in the previous post I felt the drive was not great and the four wheel pickup was not so great either. I had been thinking about using parts of an Athearn drive I had on hand, salvaged from a Scale-Craft doodlebug that did not run (that I repowered with an AHM RS-2 drive, actually, more on that drive in a minute [UPDATE: and subsequently repowered again with an Athearn drive!]).
It took some effort--I used the frame from a dummy SW-1, a motor salvaged from a junker SW-1 purchased at a train show, parts from a junker AHM S-2, and one critical part from a Athearn PA-1 drive--but got it all together (it is a very tight fit) and now have an OO gauge SW-1 that runs much better than before with eight wheel pickup. If you convert this style of Athearn drive for OO it is not hard to do, be sure to add washers outside the bearings and also pull the axle somewhat but not so far that you make a dead short in the middle of the axle (a little hard to explain, but this was probably why the doodlebug did not run, I figured out--the two halves of the axle must not touch but need to be moved so that the wheelsets are solid at 19mm gauge). The new SW-1 drive still won’t pull much--four light, free rolling cars are the max--but for the local it will work great as it runs slow and sure.
This photo shows both drives from below. [UPDATE: This article has a better view of a converted Athearn drive.] On the new drive (top) I left the original Athearn sideframes in place on the rear truck. I could put AHM sideframes on, they are actually very close to OO scale, but for now I will leave it as it is. [UPDATE: I did go on and replace the Athearn sideframes on the rear truck with the correct style AHM sideframes].
I remounted the original drive that had been the Orient body under a spare C&NW body. It still runs but I will probably not re-paint it for the Orient and this unit will likely see little future use. [UPDATE: I later worked it over more with an ATSF body, then later managed to burn the motor out. It will be rebuilt or parted out at some point].
I had one other unit on hand that I had wanted to convert to OO, yet another junker AHM S-2 (or "Alco 1000"), a model that is also clearly oversized for HO (more information here), shown in the top photo. This model uses the same drive as my old standard OO drive from the AHM RS-2. All you need to do is cut the sideframes apart in the middle, re-gauge the wheelsets, and mount couplers. It is a quickie job and for pulling a train around for the kids in multiple with other units it will do great. I probably will not re-paint this unit for the Orient either; it can be a locomotive “on lease” from the SP.
[UPDATE: The Alco was later made by Model Power with a better drive suited to the Athearn conversion. For info and photos see this article. It is close to being a 1/76 model but narrow for OO.]
I don’t at this writing have enough parts left in the parts box to make any more AHM drives run but will be shopping. One other note would be although it does reduce pulling power, I have not used any of the wheelsets with traction tires on the AHM conversions. For now I am moving on to other drives. I love the better gearing on the Athearn based drive; it is a real step up.
The Orient SW-1 may be seen in operation in this video.
Also, the image at right shows where you could take the body modifications to a higher level. This model was donated to the OO SIG by Bill Gilbert, who added the white plastic additions that are visible. These give the model a bit more heft and again show us where the next level would be in this conversion.