U class Versus N class 2-6-0,what's the difference?

I have been looking at footage of the GCR event with the visiting U class 2-6-0 and at it looks almost identical to the N class, especially after I compared it with my N gauge N class locomotive, they still look the same and a quick google fails to find anything, are there any major differences?
Or even some more subtle ones, as I'd always like to improve my knowledge in this respect
Any information would be greatly appreciated

 

Primarily wheel diameter - the N has 5'6" driving wheels, the U class 6'0". There are other detail differences, some of which follow from that change (such as the lack of splashers on an N, whereas a U with bigger wheels has small splashers), some of which derive from the fact that the first batch of U class were rebuilt from K class tank engines, and some are just the natural variations you get in a long-lived and numerous group of engines.

Tom

 

Tom's beaten me to it on the fundamental stuff, so I'll chip in with the little things.

Boilers and cylinders are identical, but the boiler is pitched higher on the U to accommodate the larger wheels and the distance between the driving and trailing coupled wheels is less, because the U class design has its origins in the K class 2-6-4T. Operationally, an N is 4P5F and has more tractive effort than a Black 5, whereas a U is 4P3F and really doesn't.

There are a few detail variations of both N & U; 31806 is an ex-K class, so has more pronounced splashers than the other survivors (also has a box over the top of the expansion link). Some of both classes were re-cylindered and had the front section of frames renewed in BR days. Curved front frames and outside steampipes (hidden behind the smoke deflectors) means a BR rebuild; 31874, 31806 and 31625 were all rebuilt, 1618 and 1638 weren't. The very last batch of N class locos were LHD, unlike all the rest of both classes. Sadly for those who like to view signals from the correct side of the cab, none of those survived.

 

In case you stumble across the U1 and N1 classes these were three cylinder derivatives of the U and N classes, easily recognised by the platform extending to the bufferbeam with no curved down front giving them a massive appearance when viewed from the front. There were only six N1s and at one time during my early spotting days they were all allocated to my local shed, Hither Green and I managed to cop the lot on shed one Sunday morning. Primarily freight locos they were quite common on Kent Coast trains on a summer Saturday.

 

While we are talking about the U-boats, and in particular, 31806, when it was at the NYMR I noticed that there were four (7/8" dia?) tapped holes on two machined surfaces on the motion bracket that don't appear to have an original purpose. These can be seen on the attached photo. Enquiries with those accompanying the loco did not produce an answer as to their original purpose. I did wonder if they were a throwback to the locos days as a River but looking at photos, it doesn't appear to be the case. Can anyone provide the answer?
http://www.alamy.com/stock-photo-wh...u-class-locomotive-no-31806-mid-36603516.html

 

In the motorcycle industry, which I have a little experience of, unexpected threaded holes are often associated with the use of special tools. Is it possible there once existed some kind of special jig, maybe associated with valve setting, that bolted on there?

 

even with in the classes there are differences, for instance the dragbox hights are different, 31816 and 31806 were both laid down as rivers, 1816 was converted on the production line, and a tender from one of the later builds wont couple up, there are differences in the cab profile a river rebuild has a more rounded profile, compared to the engines changed on the production line. i didnt realise that an N has the same tractive effort as an black 5, but the ashford mogols do seem to punch above their weight, 31625 seemed to aquite its self very well during the time it was active on the mainline.

 

Interesting - they don't seem to occur on 1638, for sure!

I wondered at first if they were mounting holes for the front footsteps that the K class locos originally had, but they are in the wrong place.

(See e.g. this photo of a K1 to see the general location of the steps, which also as far as I can see, does not have those holes).

https://en.wikipedia.org/wiki/SECR_K_and_SR_K1_classes#/media/File:K1_class.jpg

I wonder if they are a later modification: certainly the mechanical lubricator is modern, so maybe there are other changes?

Tom

 

I think you mean 1618, not 1816, but yes, 1618 was laid down as a River but converted whilst being built. That was the reason why, when the MHR had a fire that damaged the tender of 31806, that from 1618 could be used as a replacement, but none of the tenders at the MHR from the other moguls would fit.

Another distinctive difference is the windows on the front spectacle plate - 1806, as a K class rebuilt, has pairs of small windows either side, where as 1638, as a pure-bred U, has a single large window. See e.g.

1638 - https://www.flickr.com/photos/104413683@N07/14650674020

31806 - http://www.deviantart.com/art/Southern-Railway-U-Class-31806-02-Cab-Closeup-446567722

(Not my photos)

Tom

 

I think you were right all along, they are for steps (well, a step). I've found a better quality paper version of that photo which shows it, and an even better one of 799. It's quite stealthy, seems to be a piece of round bar clamped off the motion bracket and bent to stay in gauge, with a single footstep at the bottom. My guess is they were to facilitate lubrication of the weighshaft and lifting link, which is boxed inside the side tank. Once they were rebuilt presumably lubrication was done from above.

 

There were also Irish versions of both classes: Great Southern class 372 was basically the N class while GSR class 393 was the U equivalent. They were generally known to British followers of the Irish scene as Classes K1 and K1a respectively, which were basically their workshop diagram designations at Inchicore. The story is slightly more complicated than that.. Some info here:
https://en.m.wikipedia.org/wiki/GSR_Classes_372_and_393
Sadly none survived.
The Metropolitan also had take derived from the same design (built from parts, like the Irish locos). I think these were class K on the Met: https://en.m.wikipedia.org/wiki/Metropolitan_Railway_K_Class
Interesting coincidence the Rivers, Met tanks and Irish locos all being K.

 

Yes, I was sure I remembered a spindly step which was what I was looking for, but only found a picture of the meaty ones! I've been able to find photos of "spindly" steps mounted off the motion bracket on various photos of class N, N1, K and U (River rebuild, but I can't find them on a pure U). Photo evidence seems to suggest that the spindly steps disappeared somewhere in the late 1920s. My guess is that you are right that they were put in place to help with oiling up on the K class and were retained on the rebuilds and the closely similar N class locos, before being done away with as unnecessary when the last series locos were built. The K class locos only had a small cut-out on the tank to assist with oiling up, unlike the large cutout on the K1 three-cylinder version.

Edit: Photo here showing the "spindly" step: https://en.wikipedia.org/wiki/SECR_K_and_SR_K1_classes#/media/File:SECR_K_class_prototype_790.jpg

Tom

 

Blimey, powerful little things then, were the U class more or less powerful?
I'm assuming less as they were built for different jobs

EDIT: spotted it in an earlier post, I was correct in my assumption

 

Tractive effort isn't everything though! Wasn't it Patrick Stirling who said something about an ability to boil water? I'd suggest that perhaps the experience of NYMR crews with 31806 gave some credence to his thoughts!

 

And Ivatt who said that there's no point having a large purse if the bank account is not able to keep it filled.

However, for the NYMR I'd argue 31806 was the worst of both worlds and an N would have been better suited. The boiler may be exactly the same, but it would be able to work more expansively for a given drawbar pull at preserved line speeds, whereas I think @Steve mentioned having 31806 at full regulator in full gear.

The SR used the N class in the West Country taking 200 tons out of Ilfracombe with 1:36 off the platform end and Holcroft details their use on 650 ton freights on a 1:120 ruling grade, either of which converts to quite a reasonable load on the NYMR (I make it 241t or 265t assuming 1:42) but the U class weren't used for anything like that.

 

The ability of 31806 to haul (and start) 7 coach trains up Goathland bank was never in question. It was the ability of the boiler to continue to supply the necessary steam at the required pressure that was the problem. The usual thing was for the pressure to slowly drop until it reached beyond the point of equilibrium when it was necessary to stop and recover. It did make it on a few occasions but it was always a close run thing. 'Torgomaig ' can give far more detail than me as he was shovelling on at least one occasion. I merely watched from a distance.

 

Thanks for clearing up the mystery for me.

 

There is a clearer picture of the step here in the early shot of 31806 as A806 before conversion. It does appear to be an oiling aid.
Clicking the picture takes you to a bigger image.
http://swanagemoguls.com/aboutthelocos/u-class-31806-bio/

 

I'd suggest that 7 coaches behind 31806 on a steeply graded line is pushing your luck somewhat. We ran her with 6 very occasionally on the Mid Hants with no problems but the feeling was always that this was a sensible limit. Fantastic locomotive though and a superb steamer which punches way above her weight. Once she starts superheating there's no stopping her.

 

Agree. I'm pretty certain that 1638 took 7 to East Grinstead on test immediately before re-opening (1 in 55 gradient), but the more usual limit was 5, and occasionally 6, which gave a bit more in hand and saved having to work the loco completely flat out.

Tom