A little more playing with my new back to back.

I've always found my Hornby 50s to be particularly bad runners, so I've removed the wheels of the one I have to hand here (50037 in early NSE)

Testing has shown that on this loco, 3 axles were perfect, and 3 have seriously bad wobble. Looks like the cause of this is the plastic centre deforming when the new wheels were pressed in.

My first thought was to fit Ultrascales instead, however it looks like at some point Hornby changed the design of the chassis so they no longer fit.....

So the evening has been spent trying to force them back into shape.....

edit:

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