Optimizing the AML Metal Roller Bearing Truck

Optimizing the AML Metal Roller Bearing Truck

Ted Doskaris

March 23, 2013

Rev GE-A


American Main Line (AML) has followed USA Trains (USAT) in making a 1/29 scale metal freight truck that emulates a prototype roller bearing truck.

For a couple of AML car application examples, their metal truck is used on the Bethgon coal porter and PS2 4750ft3 covered hopper cars.

Example Bethgon hopper cars on an 8 foot diameter track curve are shown below.


An example PS2 4750ft3 covered hopper on the same 8 foot diameter track curve is shown below.


A comparative background about emulated roller bearing type trucks

Shown below are various model train companies, including AML, that offer plastic or metal roller bearing type freight trucks in 1/29 scale.


Now to the AML metal roller bearing truck

The AML truck is equipped with excellently made wheels (best of which had been done in a very black non painted finish)



Irrespective of wheel finish, during operation the AML truck can suffer from squeaking noises, usually noticeable on curve track. This is because the brake shoes can come in contact with the wheel flanges.

The reason the wheels can rub a brake shoe is caused by the combination of two things.

(1) The axle/wheels can walk toward one side of the truck during operation.

(2) The truck's design is such that the side frames are pigeon toed.

To illustrate this, shown below is a fairly easy remedy by modifying the brake shoes.



Now, let's study how a competitive brand metal roller bearing truck is designed that does NOT exhibit such problems.

Shown below is the USA Trains (USAT) metal roller bearing tuck.



Note the USAT truck is designed with spreader straps attached to the lower part of the side frames that serve to keep them parallel with one-another.


Now compare the AML truck in the following picture shown having an expedient remedy - really only suitable if one had come up with a quick fix in the "field":



Note the pigeon toe affect is removed as the tubing forces the side frames to be parallel with one-another.


The remedy shown in the picture below is more permanent; however, the side frames still retain their pigeon toed affect.


The remedy shown above works well, but it is not the best since the axle tips are not fully supported by the bearing pocket of the side frame since the bearing surface within the side frames are not parallel with the axle tips that engage them. Furthermore, over time with use, there would be a greater tendency for an oval pattern to develop in the bearing pocket that may result quicker as wear takes place.


The best remedy using a fabricated brass spreader strap having spring action is shown below.

AML Wheel Squeak Fix -  Side frame spreader spring


Using the metal brass spreader spring allows the placement of spacer washers on the axle tips to limit lateral axle movement to virtually nothing. This eliminates axle walk which reduces wheel flange angle of attack against the rail head with respect to operation on curved track; thus, reducing drag to a minimum.



Fabrication of the side frame spreader spring

A "U" shaped spreader that acts as a spring against the truck side frames can be fabricated from brass. Brass can be purchased in a sheet that is 0.015 inch thick - shown below.



Shown below are details of the spreader spring. (Note the brake shoes do not need to be beveled for this remedy.)


Shown below is the simplicity of installation.


Truck disassembly & reassembly for installation of spacer washers

In order to install spacer washers on the axle tips, only one of the truck's side frames need be removed so the axles can be pulled out.

The truck disassembly is shown below.


After the truck is partly disassembled, the spacer washers can be installed on the axle tips. This is shown in the following pictures.



With the trucks now completed and equipped with the brass spreader spring keeping the side frames parallel (no more pigeon toe), the truck's axle / wheels with the spacer washers can roll freely without binding. Shown below is the truck mounted on the PS 2 4750ft3 car.


Shown below is an end view of a car with the trucks installed - note that the truck side frames are parallel.





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