Aristo-Craft U25B & Potential Instability


Aristo-Craft’s U25B and its potential instability
Ted Doskaris
May 14, 2007
Revision GE-B

The Aristo' U25B loco employs a rather odd truck pivot design that resembles Aristo's passenger car trucks - that being the offset pivot - but the loco has an added plastic adapter plate inclusive of a 4 metal roller arrangement to apparently reduce friction when the trucks pivot. This loco appears to have been designed this way for tight curve train operation as it is specified for 5 foot minimum diameter curve track. In this regard, the offset pivot arrangement is of benefit for tight curve train operation by reducing the amount of front and rear overhang at the coupler ends of the loco that projects toward the outside of the curve, albeit with the trade-off of a bit more belly overhang.

Some folks with this loco have experienced a wobble or list to one side that would seem more aggravated when rounding curves - maybe because of those rollers falling out or wearing of the under side plastic surface of the loco’s frame. My U25Bs are still too "new" as to use, so I have yet to experience any stability problems and associated derailments at this time. Adding more weight within the fuel tank area that affords a low center of gravity can be expected to help improve stability – albeit in a difference sense. This will also serve to improve the loco’s traction.

The below pictures are of my Union Pacific U25B that happens to have the newer ball bearing type motor blocks.
However, this is not relevant to the offset pivot hardware that the U25B has as this is the same for the older style non ball bearing trucks of my Southern Pacific U25Bs.

The pictures may help with respect to lubrication, however, I would caution the use of Aristo's Electralube given my experience with cracked plastic journals on other Aristo rolling stock.

Again, the Aristo-Craft U25B loco uses an adapter plate with pivot rollers to implement an offset mounting of its 2 axle power truck. This method affords a shorter coupler end overhang (with the trade-off of a bit more belly overhang) that is helpful on tighter curves.

Below are upside down views:

The Aristo-Craft U25B power truck offset mount adapter plate includes pivot rollers to reduce friction: