Well, that proved interesting. I removed the two offending driving wheel springs and I confess that I was surprised when that didn’t fix anything. The restricted movement still remained, so further investigation was required.

Looking a bit closer revealed that the problem was being caused by the compensation beam hitting part of the ashpan/gearbox housing arrangement.

Once I worked out the issue my first thought was how the devil do I get in there to cut out some material to allow more movement. I couldn’t see how I might get a piercing saw in and although I do have a shallow bladed razor saw, that was too deep to go in. The last resort saw wise, was to try a hacksaw blade. That too wouldn’t fit. Then I realised that if I unscrewed the motor retaining ring it might be possible to get a milling cutter in.

I gripped the chassis in the mill vice and with a 2mm two flute slot drill I carefully milled out a slot either side taking care just to go through the two layers of etch without hitting the compensation beam.

Now I just need to refit the spring castings