Discussion in 'Steam Traction' started by D6332found, Jan 29, 2017.
How do you combine a monoblock cylinder with divided drive? Is the middle connecting rod very short?
The first batch B17 class was built by the North British Locomotive Co. in 1928. The LNER found itself in need of a modern design of express passenger type to meet the needs of working increasing train weights on the ex GE. These lines presented a problem because of limits imposed by their engineering. A batch of Pacifics would sole the problem but the permitted maximum axle loading made this option impossible.
Some of the K2 Moguls were transferred to the GE section in 1924 and these carried out a substantial amount of top link passenger work from Stratford shed. All variants of the two cylindered 2-6-0s had a maximum axle load of 18 tons or more which gave them a far higher adhesive weight than that of the 1500s which had an adhesive weight of 44 tons but useful engines that they were they offered only a stop gap solution to problem.
The LNER design offices were very busy at this time and though a range of options were considered progress on obtaining a satisfactory design was slow. The original specification was for a 4-6-0 based on the D49 design with a maximum axle loading of 17 tons. Many options were tried including a tapered boiler and fluted brake hangers in order to save weight but the Locomotive Running Department was unsatisfied with the designs.
North British had recently produced the LMS Royal Scots and so Lord Faringdon approached Sir Hugh Reid in order to relieve this bottleneck . North British presented two designs, one of 18 tons axle loading and one of 19, not quite what was wanted but the 18 ton design was chosen.
North British had built a batch of A1 Pacifics in 1924 and the design of the 4-6-0s owed much to this experience. The design was modified by the LNER with an increase in cylinder bore being requested and an increase in firebox length. Reading the history of the NB built A1s reveals that they were not as satisfactory as the Doncaster built engines and the fact that the B17s revealed problems brought about by the need to save weight comes as little surprise. What the LNER obtained might be termed was what we would call today a Royal Scot Lite. Too light as it turned out.
Some aspects of the design were good but they were built a little too lightly. The inside cylinder was set forward (Royal Scot influence) and had a short connecting rod but the position of the conjugated gear being the cylinders proved to be a good one and the class was not subjected to the influence of an inside valve gear presenting very different results to those of the outside gear. The boiler was based on established LNE designs and went on to be highly regarded by later boiler designers. The published record shows that the engines could perform very well, sure footed and sensitive to small adjustments in cut-off, they were fast and capable of handling good loads. They were also good looking engines.
So what is there not to like? They had to be built down to a weight limit which was inevitable in the circumstances though quite what the maximum axle loading was after the design had to be strengthened is another matter. The ride was criticised and though this could be kept reasonable given the correct attention English's findings were hard to escape from and their the influence of their design heritage was another matter. The crew of the Royal Scot when working out of Kings Cross during the Interchange were hailed by the LNE men and told to keep their cab doors closed to avoid being shaken off. Reputations do circulate.
The LNER proved that it was possible to create a locomotive with a 17 to axle loading with the creation of the V4 which proved to be very successful on trials on the GE section.
The B17 was a worthy design when its circumstances and requirement specifications are taken into account, as are so many other designs. Yes it did have a short inside connecting rod and no the cylinders were not monoblock.
There was a good two part appraisal of the B17s in Trains Illustrated in 1960 written by Dick Hardy under his pen name, Balmore. There was another consideration that would have precluded a Pacific, the size of some of the turntables on the GE Section at the time. It’s why those destined for East Anglia had the short GE tende.
I too was thinking about Mr Hardy. His experience was that the B17s were very variable. Here's a quote :
'.... when in feb 1949 I was told that two more were coming from Lincoln [to Woodford Halse] my heart sank. Nos 1647 and 1667 were two of the hardest and most uncomfortable old cabrankers it was ever my misfortune to come across.
[He was told to transfer two a couple of months later to the Norwich Division] 'My instinct was to forward the two latest arrivals but I was foiled because the agreement that the mileage before transfer of passenger engines must average 25000 had been imposed and these two had each run up something like 45000. No 1647 had to go and 1669, quite new from the shops, went with her. But no sooner had this been agreed than I was told I was to move from Woodford to Ipswich..... one of my first duties at Ipswich was to welcome this pair as just transferred to my new depot. So I was lumbered with the unspeakable 1647 for another 20000 miles during which time she was confined to the 5.25am Yarmouth goods and the 7.23pm Yarmouth to Ipswich stopping train. She was a low pressure engine and in her original condition would not steam, nor run, nor ride well; yet after shopping she returned with a high pressure boiler and ran for thousands of miles after that without serious complaint.'
There are other stories of the stud at Stratford in later years and dodges such as giving the worst ones on a summer Saturday to country crews to struggle down to the coast with.
But they were very good looking locos.
I'm just reading Grafton's biography of Edward Thompson at the moment...
At risk of being branded a heretic, I think a Thompson rebuild would be nice - A B2.
100A boiler, B1 cylinders x2, and 6'8" drivers. Basically a 6'8" B1.
True enough, it was another factor. I suppose that if the civil engineering side did not present any significant problems then the cost of rebuilding/replacing the relevant turntables would be relatively insignificant. In later years it was observed that if the lines concerned had been improved as required then the V2s could have been introduced and this would have saved a great deal of trouble. If we look outside the UK the Austrian State Railway 310 class had a maximum axle loading of of 14.37 tons and an adhesive weight of 43.4 tons with a locomotive weight of 84,64 tons, this design was too big for the UK and GE but is indicative of what could be done; and this in 1911. The designer maintained that to save 1,000 kg you didn't try to do it in one place but rather in 1,000. I find this to be illuminating.
Indeed and why not? Another future project for the A1SLT......
17 ton per axle was indeed the original aim, but 18 tons is where they ended up. Spirit of Sandringham will be heavier than that as the frames are thicker than the original designs.
The cylinders were indeed NOT monoblock; it should be noted for the new build that the cylinders will not be cast but fabricated, as per the posted article by Wozzy18. The middle cylinder was further forward than the outside cylinders, to add some length to the inside connecting rod.
As for the rough riding, this was actually generally attributed to poor maintenance - those locos that were maintained by their own crews didn't seem to suffer. The Spirit of Sandringham design uses roller bearings not plain, and has various design modifications to all help, including changes to the spring design.
Not sure how I got the impression that these were 'monoblocked' BUT the inside cylinder could not have been far ahead of the outsides, so a short connecting rod was still involved, hence a combination of conjugated valve gear driven from the second axle with a short rod and a single throw leading crank axle is almost certain to lead to rough riding. The late Kim Malyon told Me of the problems that He and Bill Harvey experienced at Ipswich in keeping the rear axleboxes and hornblocks in check.
I have to be honest in saying that I cannot see any reason for employing divided drive on a three cylinder locomotive
The NB could not produce a design capable of meeting the requirement the 18 ton design which was accepted by the LNER following some modifications and these engines also undoubtedly ended up came in at over 18 tons following action taken to strengthen the frames.
The poor riding was attributed to poor maintenance but this was not the full story. The springs design was changed looking into the impact of defection rates and damping and I believe axlebox wedges were introduced and diligent maintenance could keep the riding reasonable but English had a theory that there was another factor, looked into it and did the maths. In the land of modern day occasional use you may not want or even need to follow his thoughts.
What is regrettable is the fact that UK locomotive designers lacked some of the design skills to be found in Europe.
Or have drivers 6 feet 8 inches
My hero mr Ravens B16 had neither and lasted longer
How many reasons do you want? Major ones are to avoid the need for the middle cylinder to be steeply inclined to keep the motion clear of the front driving axle; and dividing the stresses between two axles. The balance between those and reasons in favour of unified drive was for each designer to decide, along with many other engineering compromises. I find it not at all surprising that different designers came to different decisions.
For what it's worth all resons are 'Valid', however the workings of a locomotive chassis are somewhat 'flexible' in that not many other types of 'engines' have spring mounted crankshafts, so putting all three throws on one axle keeps the forces 'acting together', I appreciate that the original 'Bulleids' had unbalanced crank webs, which led to at least one axle breakage, but that was 'design' rather than 'type' that was at fault, so just consider divided drive for a moment, and think about the spring mounted single throw leading axle with outside coupling rod crankpins at 120 degrees, I mean who would think that that was a recipe for dancing around? then combine this with a short connecting rod (the inside cylinder wasn't that far further forward) and conjugated valve gear, which SHOULD if in good order give the same valve events as the outside cylinders, it really leads to a rough ride. Basically it makes raising the middle cylinder and arranging a 'funny' angle on the cranks the easy way out.
Meanwhile in other news. The group behind the Spirit of Sandringham are beavering away getting bits and pieces together for their new build locomotive. Having acquired the parts collected by the other B17 group.
Understandable hint of frustration duly noted. Who's moderating today? Ooh ... morning @Pete Thornhill, could the 'Finances of the Big 4' posts have their own thread, so's we can give the B17 folks their thread back, pretty please?
Duly noted and sorted - https://www.national-preservation.com/threads/big-four-finances.1419202/
Moving to CTL Seals premises in Sheffield has been a very positive move for the group building Spirit of Sandringham. The facilities there are excellent, as evidenced by the progress being made on Clan "Hengist". The close proximity of William Cook Cast Products and Owen Springs of Rotherham is of great help in keeping transport costs down, and their collaboration with the A1 Steam Locomotive Trust is certainly proving to be equally beneficial. Interestingly William Cook are proud of their association with new build locomotives as the attached page from their website shows - https://www.william-cook.co.uk/gb/product/heritage-rail
I just thought that I'd better point out that despite My opinions of divided drive on three cylinder locomotives, I have no doubt that 'Spirit of Sandringham' is a very worthwhile project and that the team behind it are well up to the task ahead, the shortcomings inherent in the design should not give much to worry about in 'Heritage' conditions where much more attention can be payed than in everyday revenue earning service.
Unless of course you were writing tongue in cheek.
Was not a loco to this specification actually built by the LNER in 1943, when B3 6166 was rebuilt to a b3/3. It was reputedly highly regarded but due to frame fractures was scrapped in 1949.
Must admit I was thinking of a different way to mention, "Thread drift...........!"
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