Congratulations!

You are the second in as many weeks to pose the same enquiry!

So summarising the basic advice given on that:

1) First things first… Never try to operate a dry regulator, except perhaps once very carefully to see if it does move. If it doesn’t, don’t force it. This is because if it stuck on scale, moving it could score the valve face.

2) The bush and its seal in the backhead could be seized, especially from long storage. So investigate that simply by removing the gland nut. The gland might be an O-ring, graphited yarn or something a bit more “sophisticated”. It is worth renewing anyway.

3) Remove the inner dome and examine the regulator itself, which I think on this locomotive is a disc rotating on a circular face to bring drilled ports in line. If it is scaled up, use ordinary domestic scale-remover – the sort applied with a cloth of brush. Wash it off with soft water – living in a hard-water area I have just used rain-water similarly in overhauling the fittings on a 7-1/4″ gauge version of the same engine.

Yours looks as if it has operated with similarly hard water, which is why I suspect scale as well as probably solidified gland packing.

That should cure it!

While the inner dome is off see if the boiler could do with descaling. Even if not, it is well worth giving it a good washing out.

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Now for that main bush in the backhead.

It should be held by studs and nuts, not screws – especially slotted ones!. Same with the inner dome) If you remove the flange there may be enough of the broken ones protruding to grip them with pliers and very gently ease them out.

I would help them by supporting the boiler standing on its nose, and leaving it overnight with ‘Plus-Gas’ or similar penetrating fluid on them. Not WD-40 unless you really have nothing better. It will work but not so effectively.

If not, I would suggest making a dummy version of the flange in mild-steel with the holes for the broken screws drilled tapping-size or smaller only, to be screwed on to guide drilling the broken bits out. Be very careful not to break through into the boiler… though that have already been done. Clean the threads with the appropriate bottoming tap.

Only three or four complete turns of a fastenings actually do anything but more would be better if the thread is not in best condition.

Make a set of studs from stainless-steel, but do not use stainless-steel of the same grade for the nuts as they might gall. I would use both stainless studs and bronze nuts (or brass nuts, as these are outside the boiler). You could use plated mild-steel nuts, but smear some copper-based anti-seize grease on the threads.