@Ted S....
Here's pics of the engine on 031 curve; outside curve both sides of engine:
Here's the inside curve; both sides of the engine:
And an overall pic of the engine:
The engine does "fit" on 031 curve. All the front driver wheels appear to be firmly on top of the rails.
But with the front drivers pivoted to the right of the engine (looking at it head-on shown immediately above) there is absolutely no side-to-side play between the drivers and engine body.
@DMASSO....
That could very well be a cause (if there is one considering the test done above). I'll know once I open the engine up to repack the smoke unit.