Wheelset has no play from side-to-side

Zinc pest- contamination in the diecast truck block that causes swelling of the metal. It's not a common failure but is one that can and does happen to some batches. Again, comes from contaminates when the zinc alloy was cast, and then over time the impurities oxidize causing the metal to deform.

Edit- it's the process of elimination. If the wheels are not bent, not distorted from their own zinc pest, if they didn't move out of gauge on the axles- the only other answer is the truck or drive block body changed shape/dimensions.

Stuff I personally have seen failures on:

PCC trolley trucks

3 different articulated railking challengers- specifically the motor mounts which also form the articulating mount for each drive block.

Smoke unit diecast housings- the turbines and a few other engines over the years

Entire drive block assembly on some of the railking hudsons

Example picture grabs all from this very forum

K-line smoke unit showing the cracking nature

Oh so true Vernon!!!!

When will we be free from this plague???

Peter.....Buco Australia.

@Buco posted:

Oh so true Vernon!!!!

When will we be free from this plague???

Peter.....Buco Australia.

Never. As long as mistakes and shortcuts are made during casting, defects in the source materials, remelt and recycling of the waste, all introduce the possibility of contamination.

Doing it "right" does cost money. Sadly zinc pest takes long enough to form, it's not covered by warranty. At best the manufacturer does another run or replacement parts to maintain reputation- but honestly- other than saying you will never buy again- and lots of people say that and still give in later.