What is the difference between the BR standard 2-6-2 2mt an 3mt tanks.

[cypherman]

Hi all,

Was just looking up pant schemes for BR 3mt tank and could not notice just how similar they are. So my question is just what is the difference between the BR standard 2mt an 3mt tanks. Is it possible to convert 3mt into a 2mt and how easy it would be.

Edited June 16, 2020 by cypherman

[SRman]

Just about the only thing they have in common is the wheel arrangement. The 2MT tanks were basically an Ivatt LMS design very slightly modified, while the larger and heavier 3MTs were not based on any previous design, but used a modifed GWR boiler design. If you look closely you will find the locomotives look quite different from each other, with very few shapes or proportions bearing any resemblance to the other.

[Il Grifone]

The 2MT is a much smaller design. I wouldn't like to say conversion is impossible, but would be very difficult.

EDIT

Beaten to it!

Edited June 16, 2020 by Il Grifone

[woodenhead]

A 2MT tank is a development of an Ivatt 2MT and that would be a more appropriate starting point from which to create a Standard 2MT.

 

https://www.bluebell-railway.co.uk/bluebell/locos/84030.html

 

A 3MT uses a GW derived boiler.

[Hal Nail]

16 minutes ago, cypherman said:

what is the difference between the BR standard 2mt an 3mt tanks.

 

1mt?

[The Johnster]

You'd certainly notice it if the two models were placed together.  The 2MT is smaller in every respect except the leading and trailing pony wheels, and lighter as well.  Very few parts of any size are interchangeable between the classes.  There is certainly a 'family resemblance' between all the BR standards, and this is because they were all much influenced by late LMS practice under H A Ivatt.  The 2MT is as has been said a direct derivative of the Ivatt 2MT, with interchangeable parts between both classes and the 2-6-0 tender versions, and the main differences are confined to a different cab side on the BR mogul and a continued angled running plate over the cylinders as opposed to the gap on the Ivatts.

 

Similarly, the BR standard 4MT 2-6-0, the 76xxx, was only stylistically different to the Ivatt 4MT 43xxx mogul, though the chimneys were different.  The 3MT tank was drawn up and built at Swindon, and can be regarded as a development of the GW's long standing and successful 'large prairie' type, but built of BR standard components and a domed version of the GW no.2 boiler.  The resultant smaller cylinder size meant that they were less powerful than the large prairies, which were rated 4MT by BR (as were the GW small praires, btw, interesting as these locos are more of a size with the Ivatt/BR 2MT tanks), but they were lightei and had a wider route availability.  There was a tender version, the 77xxx, of which only 15 were built but which made a good name for themselves on some weight restricted and hilly routes.

 

To summarise, the GW small prairie is twice the power rating of the similarly sized Ivatt/BR 2MT, the BR designed version of the GW large prairie was less powerful than the GW's version that used the same boiler, and the GWR was by definition better than the LMS or BR.  Discuss.

 

I'm heading for my bunker...

[Steamport Southport]

The 3MT is virtually a Stanier 2-6-2T with the later type of large boiler which had already been fitted to some of them. 

 

I've never understood the idea that they were designed at Swindon. It already existed and was just tweaked by Riddles.

 

https://transportsofdelight.smugmug.com/RAILWAYS/LOCOMOTIVES-OF-BRITISH-RAILWAYS-MIDLAND-REGION/262T-LOCOMOTIVES/i-6nXPwBz/A

 

 

 

Jason

Edited June 16, 2020 by Steamport Southport

[Tim Hall]

I have a Bachmann Ivatt 2MT that is mostly converted to an 84xxx (cab profile is incorrect). I enclose some snaps for dimensions (handily they are in the display cabinet whilst it's 1985 on the layout)

[Il Grifone]

3 hours ago, The Johnster said:

omis

 

To summarise, the GW small prairie is twice the power rating of the similarly sized Ivatt/BR 2MT, the BR designed version of the GW large prairie was less powerful than the GW's version that used the same boiler, and the GWR was by definition better than the LMS or BR.  Discuss.

 

I'm heading for my bunker...

 

It's self evident (see below).

[Compound2632]

3 hours ago, Steamport Southport said:

The 3MT is virtually a Stanier 2-6-2T with the later type of large boiler which had already been fitted to some of them. 

 

I've never understood the idea that they were designed at Swindon. It already existed and was just tweaked by Riddles.

 

In its turn the Stanier 3P 2-6-2T was a taper-boiler variant of the Fowler 3P of 1930 - the weediest-looking locomotive of LMS design. The BR standard 3MT is the handsomest-looking of the three.

[The Johnster]

I seem to remember reading that neither the Fowler nor the Stanier versions of the LMS 3MT prairie were particularly highly regarded, and neither were Thompson's LNER prairies.  Fowler's 2-6-4 tank, by which I mean the early LMS loco he signed off on, was regarded as a success, and was the progenitor of a series of 2-6-4T locos culminating in the BR standard 4MT.  The Southern never really bothered with prairies, and dropped out of the 2-6-4T game after the Sevenoaks accident except for trip freight work with the W class.  

 

So, what was it about prairie tanks that Churchward got right and nobody else seemed to quite grasp?  Churchward's small prairies lasted until the end of steam, and the large prairies were still being built in 1949, though these locos are a very confusing bunch with two separate 31xx classes, two types of boilers, and a bewildering variety of of boiler pressures and wheel sizes under Collett's tenure which suggest he thought there was room for improvement.

 

Or, put another way, what was it about 2-6-4T locos, successful on the LMS and Metropolitan and arguably an unfulfilled potential on the Southern, that the GW didn't 'get'?

 

Ivatt's small prairie is a different beast, an attempt to replace a plethora of pre-grouping 0-4-4T or 2-4-2T with a modern loco suitable for branch work, alongside a mogul to replace an even greater plethora of 0-6-0 tender locos, a type the LMS had only stopped building during the war.  It is still undeniably easier to prepare and probably cheaper to build than a 45xx, but the fact remains that the 45xx is a much more powerful loco at around the same size.

[The Johnster]

I must agree that the 82xxx is the best looking out of the Fowler, Stanier, and Riddles trio, but I'm not sure how much we should attribute to each CME.  Fowler signed off on a very Derby design, probably the first time Derby had tried to build a modern loco since the S&DJ 7F, and I am sure a lot of old hands at Derby shook their heads in a 'told you so' manner when it proved a failure in service.  Stanier then arrived and signed off on an 0-4-4T that was clearly nothing to do with him, and a pure Derby traditional loco.  He then had a look at the prairie and, I have always assumed, tried to convert it into a GW large prairie, but the small boiler, a repeat of a major failing of the Fowler, was simply repeated in a taper form to no apparent purpose.  Neither loco could be called a success.

 

So, we must ask, why did Riddles have another go at this poisoned chalice?  Well, despite what has been said about 'tweaking' the Stanier 3MT, I don't think that's what happened.  Swindon wanted to build yet more 5101 large prairies to replace the larger pre-group South Wales locos it had already 'Swindonised', the likes of the TVR 'A' or Rhymney 'P' classes, which were coming to the end of their useful lives.  These were locos with 5'3" driving wheels and in South Wales terms this made them passenger locos for the busy suburban work of the area; the GW's default answer to that was the large prairie.  

 

Marylebone was having none of it, and quite right too; they'd had trouble with the WR over Britannias and the region had requested more Castles, Halls, and 28xx when there were satisfactory BR standards available for each of those roles.  So Swindon was given the job of designing a replacement for the 5101s, overseen by Riddles who set the parameters, and this resulted in the 82xxx and 77xxx locos.  Swindon was basically told to make 5101s out of BR standard components, and the 82xxx has little in reality to do with the Fowler and Stanier locos beyond the coincidence of approximate size.  

 

The 82xxx were, to my mind, a well proportioned and handsome beast, and if they never covered themselves in glory they were efficient and effective locos during their short lives.  In South Wales they had the advantage of a boiler the men were familiar with from the 5101s and the 56xx, and the larger driving wheels gave them more 'range' than a 56xx; they could manage the work of the locos they replaced and were easier to prep and dispose.  I have distorted Rule 1 to no mean extent to have one on Cwmdimbath!

[SRman]

4 hours ago, Tim Hall said:

I have a Bachmann Ivatt 2MT that is mostly converted to an 84xxx (cab profile is incorrect). I enclose some snaps for dimensions (handily they are in the display cabinet whilst it's 1985 on the layout)

 

I like what you have done with the 84XXX, Tim. The cab corners can be rounded off a bit to get nearer to the BR profile. I did something similar to a Bachmann Ivatt to represent one of the later batch sent to the Southern Region with modified cab roof profiles and gutters ... well, I rounded off the cab roof sides but left the gutters intact. Being black, the paint is easily touched up again.

[Tim Hall]

4 hours ago, SRman said:

 

I like what you have done with the 84XXX, Tim. The cab corners can be rounded off a bit to get nearer to the BR profile. I did something similar to a Bachmann Ivatt to represent one of the later batch sent to the Southern Region with modified cab roof profiles and gutters ... well, I rounded off the cab roof sides but left the gutters intact. Being black, the paint is easily touched up again.

I bought it last year for £40 largely as it is, though it has given me the idea to turn my 2nd 2-6-0 2MT into a 78xxx a lot cheaper than Hornby want for their upcoming one.

Edited June 17, 2020 by Tim Hall
Typo

[Compound2632]

9 hours ago, The Johnster said:

Fowler signed off on a very Derby design, probably the first time Derby had tried to build a modern loco since the S&DJ 7F, 

 

The 4P 2-6-4T came out in 1927, three years before the 3P 2-6-2T, and I think one would struggle to argue that that wasn't modern in comparison with the 4F and 4P compound. The larger passenger tank engine was a resounding success and, by some accounts, preferred by the footplate staff to the later Stanier and Ivatt developments. The Derby LDO had been sketching out large tank engines ever since the 4-4-4T proposed in Johnson's last year; unfortunately the only thing that came of that was the 2000 Class 0-6-4T but many of the ideas that were to go into the 4P had been mulled over. One shouldn't judge the talent in the drawing office solely by the locomotives they were actually allowed to have built - the operating department seem to have had rather old-fashioned views. In the light of the 4P, it's curious that the 3P was such a dud. No doubt that was why the operating people said, more 0-4-4Ts, please, we know they're up to the job.

 

Anyway, what about the 3-cylinder 4-6-0s? Both classes look modern to my eyes, but then so does anything built after c. 1902.

Edited June 17, 2020 by Compound2632

[The Johnster]

I stand corrected; the 2-6-4 tanks were acknowledged by all to be fine engines.  I was restricting my use of the term 'modern' to tank locos, of course the Patriots and Scots were pretty much up to the mark in the 20s, as were the Hughes/Fowler Crabs, another universally well regarded loco.  Over on the LNER, they never really seemed to get to grips with 4-6-0s until the Sandringhams, which never really seemed to cut the mustard.

 

The 3MT's 'dudness' seems to be in both the Fowler and Stanier cases down to poor steaming and a congenitally inadequate boiler.  One sort of assumes that the Stanier must have been influenced by the Churchward large prairies because of Stanier's Swindon indoctrination, but there's no real evidence for this AFAIK, any more than there is for the Stanier mogul being a derivative of the 43xx.  Everyone seems to have expected that Stanier would provide GW locos for the LMS, but, apart from taper boilers, he didn't, and this was a wise move on his part; the LMS had different requirements from it's locos and used different coal to the GW.  

 

The LMS 3MTs are nothing like the Churchward/Collett large prairies.  The boilers and cylinders are much smaller, and of course the valve gear and events are very different.  I suspect the parallel Fowler boiler was the better of the two, at least in that it was a well established Midland type of known capacity and performance, but neither loco really 'worked'.  The BR 3MTs have elements of both the LMS prairies and the GW, and were efficient modern locos when they were introduced, but WR drivers expected them to be replacement 5101s, and they weren't really ever intended to be that.  WR men did not really ever think in terms of the LMS/BR power ratings and largely ignored them, as far as they were concerned the 3MTs were power class C, same as the 5101s but only on paper...

 

The LMS 3MTs don't have much in common with the 45xx/4575 either, but it goes against intuition that the smaller locos are more powerful according to the LMS' power rating system.  It is similarly strange to consider a 5MT 56xx, powerful though they were, as comparable to a Black 5, or that a loco with 4'7" wheels should be considered as a mixed traffic loco to begin with, but there is little in common between the duties typically undertaken by 56xx and Black 5s.  4'7" or ball park driving wheel was normal for 'goods', i.e. mixed traffic, locos in South Wales, and passenger locos usually had drivers around the 5'3" mark.  Mineral loco drivers were usually just north of 4'.  

Edited June 17, 2020 by The Johnster

[34theletterbetweenB&D]

17 hours ago, The Johnster said:

I seem to remember reading that neither the Fowler nor the Stanier versions of the LMS 3MT prairie were particularly highly regarded, and neither were Thompson's LNER prairies ...

They were vapourware, he went 2-6-4T with the notorious L1 'Concrete Mixer' of legendary all around ungoodness.

 

44 minutes ago, The Johnster said:

...Over on the LNER, they never really seemed to get to grips with 4-6-0s...

The LNER was in traction terms the GNR writ large, and Doncaster never designed a 4-6-0 until very late in the day when dragged off course. (And BR then found by trialling that it was the best class 5 performer, for less money than the competing Black 5 and Hall.)  Doncaster's scheme was 2-6-0 for medium power mixed traffic, (the K3 a 6MT design from 1920) wide firebox for high power: the superior path that bestowed on the financially straitened LNER more wide firebox locos than the rest of the UK combined could show.

[DCB]

Many years ago Model Railway Constructor had an article on how to convert the BR std 3MT 2-6-2T  into a 2 MT.    It was one hell of a lot of work.     I tried to make the Triang 3MT  into a model of a 3MT which was itself quite a task.

The real 3MT was a bit of a mistake, It seems the original plan was a No 4 boiler with a shortened barrel , its often quoted as having  a No 4 boiler but actually it was the smaller No 2 with a shortened barrel, almost exactly the No 3 Boiler from the  1903 2-4-2T.   The Walschaerts valve gear gave less torque on starting than the 51XX Stephenson and the cylinders were smaller anyway so they, barely equalled the smaller 1905 design GWR 45XX Prairies and never made the grade as updated 51XX.   They found their niche on frequent short distance passenger services where quick turn rounds and servicing away from pits etc were required.  Initially when designed would have been better performers than the Ivatt 2MT 2-6-2Ts and better route availability than the 4MT 2-6-4T but he routes were up graded and Sam Ell dramatically improved their steaming when the 2MT 2-6-0s proved inferior to 50 year old Dean Goods.

 Later 4MTs could use most of the same routes as the 3MT and there seemed little difference between 2MT and 3MT 2-6-2Ts which seemed to shared the same duties on the Southern Region.  They did have big cabs and comfy seats though.

[The Johnster]

This would explain the lack of 4-6-0s from Doncaster; they had good moguls and were wedded to the wide firebox.  Must’ve been coal hungry, not that ever bothered Doncaster, though.  Wide fireboxes seem to be universally successful on large locos where continuous high rates of steaming are needed, but perhaps not the most efficient solution for all types of traffic.  The ECML was responsible for the very heavy and fast fish traffic from the North Sea ports and harbours from Felixstowe to Inverness, and the K3s handled this traffic well, but I doubt their firemen were particularly find of them...

[D9020 Nimbus]

Had Gresley survived longer, Doncaster's only 4-6-0s would have been the B17s—presumably the V4 would have been made in quantity; Gresley was inclined to go for 2-6-2s — did any other railway in the UK have this wheel arrangement on tender locos?

[Compound2632]

3 hours ago, D9020 Nimbus said:

did any other railway in the UK have this wheel arrangement on tender locos?

 

There was the Paget locomotive, if you count that. Otherwise no - though common enough elsewhere. Here's Karl Goelsdorf's 329 Class of 1907 for the Imperial-Royal State Railways:

 

[The Johnster]

4-6-0s seemed to dominate for heavy main line mixed traffic work, and there is a reason for this in that the 4-6-0s were a)made very popular for express work by Churchward, who was highly influential, b) were a natural progression from 4-4-0s, though not all CMEs were good at this, and c) were also a natural result of putting bigger boilers on the moguls that had developed for heavy MT work, the likes of 43xx, Crab, K3 and the Woolwich Maunsells.  

 

In the case of Atlantics, they were often as much a progression of the late Victorian singles as they were of 4-4-0s, and advantage of the wide but hungry firebox they allowed eventually led to them being expanded into pacifics on the LNER. If you take that line of thought down to tender prairies, then they do not progress as easily from moguls as did MT 4-6-0s.  I would suggest, but do not have the engineering qualifications to do more than suggest, that there were 3 possible reasons for this.  One was that the weight distribution of a 4-6-0, if the way the tender is loaded to the back of the loco is handled properly, leads to better grip on starting, two is that the Civil Engineers preferred 4 wheel leading bogies on heavy locos that ran fast, especially 2 cylinder ones, and three is that there is, compared to a prairie tank loco where the trailing pony supports the bunker, less room for a firebox as it has to be shoehorned in just where the trailing pony goes on the tender loco.

 

The obvious exception is the V2, very successful and highly regarded.  This was a 3 cylinder loco of less objectionability to the Civil Engineer, and the large Gresley cab allowed a big wide firebox on what was a pretty big engine.  It was a power class above the 'standard' UK MT 4-6-0, the Hall/Black 5/B1/73xxx and really more comparable to a light pacific.  Express goods speeds on the ECML are legendary, and terrifying to anyone who's ever ridden in a brake van, and it may simply be that the ECML needed a faster and more powerful MT workhorse than the other railways did.  The GW and the LMS had plenty of passenger 4-6-0s that could handle fast freight work, and thus never needed anything like the V2s, and the Southern's traffic of that sort was mostly on the Western Section which had the excellent Urie 4-6-0s, engines 20 years ahead of their time when built.

 

The V4 is a less known quantity, and may be thought of as two one-off experimental locos, which eventually merged to be identical.  They were the LNER's version of a Manor in some ways, a powerful MT loco with high R.A,, but it was inevitable that Thompson would be pressured by circumstances to produce a 2 cylinder 4-6-0.  I'm sure the V4s rode better.  The B1 had larger driving wheels and was probably more suitable for fast running and better at keeping out of the way on the main lines, and the V4 wasn't light enough to solve the problem of the Stainmore route, which had to await the BR 3MT moguls.  The Bantams worked well enough though, and were certainly better thought of than the B1s, but the lighter moguls were probably just as good at the work on secondary lines in Scotland, and there were plenty of ancient but functional 4-4-0s about as well.