Articulating USA Trains and Bachmann plastic arch bar freight trucks.
It is my belief that articulation of the trucks on our rolling stock is one of the key ingredients to reliable operation. For those who run their trains on perfectly level surfaces, this will not yield much change. For those who run their trains outdoors where track may suffer the same ills as our prototype, this will improve reliability.
First, remove and disassemble the truck.
The tools you will need to modify the truck bolster are a small flat file and a counter shink. The is file for altering the tabs that go into the slots in the side frame, and the counter sink to put a slight chamfer the edge of the screw holes in the bottom of the tabs.
The truck bolster will look something like this before you start.
Using the small flat file, remove any flash or high spots on the sides of the bolster tabs, both sides. This will facilitate the tab being able to move more freely in the slot in the side frame. Remove small amounts and test fit often to not remove too much material. The intent is to make a smooth and consistent surface.
Using the small flat file, create a taper on the sides of the tabs, no more than about 5 degrees (10 degrees total angle). This will allow the side frame to rock on the end of the tab giving the desired articulation.
On to the side frames. The tool needed for altering the side frame is a small tapered round file, commonly referred to as a 'rat tail' file.
Using the small tapered round file, carefully slot the screw hole in the bottom of the side frame roughly one screw diameter each side of center.
Reassemble the truck as shown below.
A couple notes on reassembly. When assembling the screws attaching the side frames to the bolster, apply a small amount of a low or medium strength thread locker to the leading end of the screw before assembling. Tightent the screw almost tight, but leave it loose enough for the side frame to rock a bit. The thread locker will keep the screw from coming loose in operation.
Lubricate the journal boxes before installing the axles in the journal box. It is much easier to do that now while the truck is disassembled. My preference is to use a plastic compatible White Lithium grease available at your local auto parts stores. Be sure it is plastic compatible.
Something that has bothered me about the Bachmann and USA Trains trucks is the excessive amount of side play the axles have in the assembled truck. To reduce this side play and make a more stable truck, I install 3mm nylon washers on each exle end (4 per truck). I purchase them from McMaster-Carr (part number 91545A420) or Fastenal (part number 11512181).