Very easy going Martin!

Quote from: port perran on February 02, 2026, 08:00:26 PMSteinar Ytrehus

I've been listening to his work his evening.
Works for me but what do others think ?

Suitably bimbly for watching trains or concentrating on fiddly work on the layout or rolling stock maintenance, imho! Like it!

As I expressed interest in almost all of the Gresley versions, I decided to only plump for four of the Staniers, one of each pattern, and only in BR lined maroon, as these would match the only suitable loco I have for push-pull operation.  I would run a 2-coach push pull train: fitted comp, DBT; alternating with a 4-coach pull-only: plus 3rd & BT. I expect that someone will eventually tell me that my particular choice would, prototypically, never be seen running together! Oh well, I did my best to help get the project to the finishing post ... currently >80% . . .

Both the full brake and the refurbished buffet are now in tooling ... remains to be seen which livery versions were most popular/ they decide to go with ...

It's Maybe Fine in Practice but it Won't Work in Theory


Hello Chums

Quote from: Train Waiting on November 21, 2025, 10:17:49 AMI'm wondering about perhaps posting some 'Occasional Specials' covering specific matters that were either left out of the mini-series or glossed over.

Sorry for quoting myself - not good form, I know. The long and the short of it is I've now stopped wondering, so let's jolly along with:-


Occasional Special No. 1

Almost all steam locomotives are reciprocating engines of the Stephensonian type. With two, three or four cylinders, according to the designer's preference and the work to be done. We discussed this sort of stuff in the amazingly brief mini-series.

We have eminent engineers, experienced enginemen and distinguished physicists on our FabulousForum, so I'm going to loup in where the angels fear to tread regarding this topic.

Please think of a reciprocating engine, steam or internal combustion, of your choice. This could, for instance, be a Burrell traction engine, a Gardner diesel, a Rolls Royce Merlin or Velocette 'KTT' - it's up to you.

One thing you are likely to find when you take your chosen engine apart is the cylinder and crankshaft centres are in line with each other and they are fixed firmly in relation to each other by some means. Hard luck if you chose a 'Deltic' engine as your example - it has three crankshafts, so that's a lorra, lorra parts you now have on your parlour floor.

The reciprocating bits of the engine make the crankshaft/s birl round 'N' round. Often at a furious rate. I had a 500cc Velocette 'red-lined' at 6,000rpm - 100 revolutions per second. The late (and great) Mike Hailwood's 250cc Honda Six was red-lined at 18,000 rpm. Goodness, gracious me!

Our steam locomotives' coupled wheels don't quite turn at that rate. At 100mph, 6ft 2in driving wheels, as on a 'Britannia' or 'Merchant Navy' 4-6-2, will revolve at 7.5 revolutions per second or 450rpm. A '9F' 2-10-0 with 5ft coupled wheels at 90mph will achieve 8.4 revolutions per second or 504rpm. Although, hearing of this speed being achieved by a '9F' made BR motive power HQ take SuperSwift action to prevent reoccurrences. The mechanical engineering staff probably didn't require laxatives for some time afterwards.

Now to get to the point (at last!). Unlike the engines we thought about earlier, a Stephensonian steam locomotive has an interesting difference. The cylinders and the crank axle (or plain axle for two-cylinder outside-cylinder types) - the steam locomotive's equivalent of a crankshaft - are not fixed in relation to each other. Let's think about this.

Going right back to the era just after the earliest 'steam dinosaurs', steam locomotives were fitted with springs in an attempt to stop them wrecking the track. Having springs was one of the rules for the Rainhill trials, although it is believed Timothy Hackworth's Sans Pareil didn't have them. The combination of its vertical cylinders and a sprung driving axle would have resulted in a locomotive version of a pogo stick. Robert Stephenson quickly lowered the cylinders of the Rocket-type locomotive and succeeding designs to nearer the horizontal to ensure better running.

Let's take a figure for the vertical range of a locomotive's sprung axles of about 1 1/2in. Springs 'softened' with age and use between repairs, so a locomotive ready for overhaul could have a greater vertical movement than a new or just-repaired one.

Of course, our locomotive's cylinders are fixed to the frames and don't move with the sprung wheels. One would think, in theory, the resulting variations between cylinder centre line and crank axle, or driving wheel, centres would be a recipe for disaster. Hideous piston, piston ring and cylinder bore wear at least. A complete seizing-up at worst.

There is another factor to consider. When other motorcycle manufacturers were using rigid frames, or those with primitive vertical plunger rear suspension, Velocette introduced its pivoted fork¹ rear suspension. Pretty much every manufacturer followed suit, although some took their time. The pivoted fork caused the rear wheel to move in an arc under control of springs. That way, the distance between the gearbox sprocket centre and rear hub sprocket centre remained constant. Jolly good engineering, as one would expect from Velocette.

But a steam locomotive's driving wheels don't move in an arc. The axleboxes move vertically in the frames under control of the springs. This means the effective distance between the crank axle, or driving wheel crankpin, and the piston is greater at the points of maximum spring deflection. As the connecting rod and piston rod are of fixed lengths, that means the only way to compensate for movement caused by spring deflection is for the piston to move in the cylinder. One's thoughts turn to the piston being potentially pulled back into the rear of the cylinder and suchlike horrors.

As if that wasn't enough, here's another thing. Remember we mentioned that, in reciprocating engines, we'd expect the cylinder and crankshaft centres to be in line with each other? Common sense and we'd be forgiven for assuming the same always applied to steam locomotives. And our assumption would be ... wrong!

This wasn't always the case and the best examples to demonstrate the point date from Mr Churchward's time on the GWR. On some of his two-cylinder locomotives, the engine centres (a centre line through each cylinder bore) were not the same as the traction centres (a centre line through each coupled axle in succession). The engine centres were 2 1/2in above the traction centres.  Here's a couple of picturinghams which, hopefully, demonstrate this. I had such fun with a straight edge placed along the piston rods to prove this point to myself:-







You'd think this arrangement would be totally daft, but Mr Churchward's locomotives were streets (railway lines?) ahead of contemporary British types. Yes, there was a difference in connecting rod angularity at each half-cycle, but this made no difference to the efficient running of the engine. But how on earth did Mr Churchward compensate for that difference in connecting rod angularity?

Well, back in Robert Stephenson's time (in my view the only British locomotive engineer more distinguished than Mr Churchward) it was evident that there needed to be sufficient clearance allowed between the piston at maximum stroke and the rear end of the cylinder to allow for the movement of the driving wheel crank, or, from Planet's time, crank axle under the action of the springs.

In order to have the engine and traction centres at different azimuths, Mr Churchward simply allowed 1/16in additional rear end clearance for each cylinder.

So there we are, scary biscuits in theory but a practical engineering job which has stood the test of time.

¹ The pivoted fork quickly became known to all but the most pedantic motor-bicyclists as the 'swinging arm'.

One last thing to mention before I say toodle-pip. I continue to be amazed that our MarvellousModerators allow a coarse modeller like wot I am to write this semi-technical stuff. However, you'll be relieved to learn that viewers of this postington were safeguarded from the worst of my SuperSilliness by the kindness of @Hailstone and @martyn in reading my draft and commenting thereon. To you, gentlemen, my greetings and thanks.

Any remaining errors, omissions, inconsistencies or inelegancies are mine and mine alone.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Toodle-pip

John     

Can you post a photo Bob?

Or do you know the catalogue number?

As I said, I think you have a mix of BP Green (#3708) and Esso black (#3704)

Does this match with the models you have?

It might also be that their previous owner painted the corners yellow because they looked nice!

Based on your description, (but lacking a picture!) yes, the solebars should be black.

That's right! As a last resort, I could torch it

Quote from: Bealman on February 03, 2026, 07:47:56 AMWho do I report it to? Cops?

either the cops or the local council.
Doubt either will do anything, at least ours wouldn't, couldn't be bothered, or too hard.

Maybe just local council. Google abandoned vehicles in the town you live in and see if theres a hotline number or what you need to do

It's a main road.