V2 4771 Green Arrow to return?

A fabricated block could be a way forward, like the P2. It would depend on whether the highest priority for Green Arrow was retaining its originality or becoming operational. It seems that both are not possible.

 

Indeed. My point, given the persistence of the view (myth?) that the monobloc is irreparable, is that the means of repair or replacement can't assume that a fabricated replacement would be acceptable.

 

Isn’t there a question of reversibility? That is, hypothetically you could remove the existing cylinder block and preserve it; and replace with a new set of cylinders (of any construction method, it wouldn’t matter visually); but doing so wouldn’t preclude a later reconstruction of the loco with its original cylinders, albeit for static display only. So a restoration with new cylinders doesn’t seem to me to preclude a future return to “original” condition if that was deemed important. (*)

(*) As an aside on that, if the monobloc cylinders are considered a significant engineering artefact in their own right, then they are probably better appreciated in any case as a standalone item, and possibly - speak it quietly! - sensitively sectioned.

Tom

 

It's a fair question, but that then also leads into questions of preservation ethics - questions that cannot be answered definitively, and are in reality matters of judgment rather than right/wrong

 

I agree however, at least until the 2019 policy is revised, it may be assumed NRM’d be open to considering the idea if there was a source of funding. Otherwise, logically, the policy would either not have mentioned GA as a candidate or could easily have said it’d be considered only if the existing cylinders were repairable.

 

I think casting techniques have moved on since the 1930's...

 

My understanding was that initially, the plan was that 4771 would go to Doncaster temporarily whilst 990 was undergoing conservation work, and the two engines would be swapped in due course. Whether that is still the plan, I don't know. All I can say is that 990 remains on display in the Great Hall at present.

 

Capabilities especially around moulds certainly have, but so have other production methods, especially for complex one offs.

 

Interesing.

With modern tecniques and tech, its all repairable, weld can be added, machined back, heat treated, etc etc, but there is a legitimate question on preserving the original block as part of the original rationale for preservation.

If we want to preserve that, and run the machine, its reasonable to have a go at casting a new monoblock and put the old one on display.

I suspect the bigger question here is that this cannot in any way be done in isolation.
Tear out the monoblock and more will be found.
And there is the boiler.

So its almost certainly £1m before we even get out the gate... and... is it appropriate use of funds that the NRM have 2 mainline locos in ticket with all the associated costs at the same time... ???

 

One hoped the Streamlined Duchess would be top of the list or is damaging the casing too much of a risk...

 

Yes - if money was no object that would be a good way to do it. On the last point - after its removal to a museum, best would not be to section the original monobloc for display, but to make a (full sized … and working?) model of it and then section that, to be displayed alongside the unaltered original. Of course it’s vanishingly unlikely money would be found for such an elaborate solution. Possibly something could be done with a computer simulation instead, to show how everything worked.

 

Some capabilities might have improved but capacity is another matter. Who would you approach to make such a monoblock casting? You would want it defect free and the original design would be in need of examination and adjustment to eliminate any weaknesses in that design. Gorton produced these monoblocks under the oversight of R.A. Thom since they presented a challenge. Were the cracking issues a problem brought about by the design or were they the result of limitations in foundry techniques which existed at the time?

When the time came to discuss the cylinder block of the new P2 even the William Cook Group decided that they could not guarantee the outcome. The use of fabricated cylinders in preservation is not new, Talyllyn Number 1 had them fitted when first restored.

What we are needing to address in the first instance is the notion of restoring the engine to working order. Who wants to do it? The Science Museum? Are they serious or just wanting some enthusiast engagement? If they are serious it moves on to funding. It won't be inexpensive and there is seldom a good time to appeal for funds. The engine needs a full examination, this is widely agreed upon. But people are concerned about what might be discovered after the engine is reduced to its component parts but this project needs to be sold as a full package. Full assessment followed by full renewals and repairs. The only thing which is going to be a challenge is the monoblock, preservation has already dealt with everything else many times over. Actually the monoblock isn't a real challenge, the solution already exists if we need a repacement the big question is will the original block repair. Won't know until we have really thorough look and you cannot really look if the cylinders are still fastened to the frames.