Niels

How will it look with 5 feet drivers and 16 inch cylinders? If a two-cylinder Saint with 80 inch drivers can do 100 so this is limited to 75 with 60 inch drivers. Fast enough for Wales.

If You can afford it ,it has already done.Photoshop Coppercap Click Picture for enlargement.Once ,wait ,Once more.

Let me try. A Castle has two 406mm dia outside cylinders sitting 2184mm appart. Mr Garbe in Germany designed a 2-6-0( P6) with full Krauss- Helmholtz front truck and two outside cylinders sitting 2080mm apart. Prussian P6 That means a 2-6-4 with Castle wheels and cylinder dimensions could run the same routes as a normal Castle. It could even have 508mm outside cylinders and one inside with 762mm strokes and have more tractive effort than a King.And at lower pressure if wheels were 6 feet diameter

It could also be a fourcylinder simple copy of Goelsdorf 310.Would solve the UK loading gauge problems allowing a Krauss Helmholtz up front.

Inside cylinders with mostly outside valve gear pulled worlds fastest commercial steam train in Belgium. https://www.altaplana.be/en/dictionary/12.004 GWR surpassed everybody in crazyness,building fourcylinder locomotives with two inside valve-gears in 1950. GWR also sired a lot of exotic/expensive boilers with corners and tapers everywhere and never proven superior to anything. But Your evaluation of Chapelon will be true in all eternity. Lovely

The italians tried to improve performance. A4,MN ,BoB&WC used tinplate to hide lousy engineering (valve drive).

The picture was meant to show that Caprotti on Q1 was possible and would have been more user friendly. Franco Crosti was ugly everywhere.

Two extra balance rods. Benefit is very much less uncomfort and destruction of crew,locomotive,train and permanent way. A K1 can then do anything better than a B1 and is 10 tons lower mass and cost.

There are pictures in a Q1 book ISBN 0954485912 page 16 and 17? Caprotti then? Italian inside Caprotti or Stephenson Outside Stephenson or Walschaerts Waelschaerts outside to inside

It is not a poppet valve gear but four low-mass piston valves per cylinder. Try to find the drawing in first link. Cossart balance rod

Even better I think. On the outside cylindered 141TC they had to put a low mass (lots of holes) reverse rod to one end of the vertical crank that guides the heavy balancing rod. On inside cylindered engines the normal practice is to have inside-crank throw and outside coupling pin opposite.. I cannot claim to understand the Cossart valve gear and will love to see a describtion (in french if need be). The gear was not changed or altered from 1933 to 1970 and the 141TCs stopped and started an awfull lot of times

Bulleids Q1s have always fascinated me and I think they could have been improved and been best british 0-6-0 if they were not already. Bulleid went to France around 1936 to meet Chapelon and the Nord Pacific became ill somewhere north of Paris. Locomoive exchanged and the very fast schedule kept. He went forward to see the wonder engine and was impressed and very surprised It was a surburban tank Nord 141TC that had Cossart valve gear that also acted as reciprocating balance for the steam pistons. If the Q1 had had this valve gear it would have been balanced 100% fore and aft and yawing or nosing. Worlds safest and fastest inside cylindered 0-6-0. And a little easier to maintain as all valvery can be reached from outside. No eccentrics on crank and thus more robust. Nord 141 TC page 211 141 model

A three cylinder compound based on 9f parts would have been a fitting finale

A simple modification for all inside 0-6-0 locomotives can be to put balancing rods on the driver outside pins. We balance ca 50% up and down as usual with counterweigths in the wheels and the rest in the rods and that will also cancel the swaying or yawing movements. The Southern Q1 with 4 feet drivers and wide firebox can run and track better at speed if it had been made that way. Bulleid knew this locomotve pre WW2 as inspiration. Nord 141-T

Not quite. The german 2-8-2 s were all outlived by 2-10-0s The last SNCF steam haul was done by a WW1 2-8-0 and the americans went for 2-8-4 and 2-10-4s