Bulleid rebuilds - Was it for the better?

I think the benefit is far more marginal than you imply. Firstly, as soon as the desired payback was over perhaps 10 years rather than the originally planned 25 or so (say mid 1950s to mid 1960s rather than 1980), rebuilding stopped. So the business case must have been pretty marginal at best, which suggests that the originals can't have been that bad. Secondly, rebuilding prevented the class working west of Exeter, which was one of the areas where they were most needed! Not much sense in making a marginal improvment to the efficiency of a design but at the expense of completely precluding it from running where it was needed!

90% of the original fabric wound up in the rebuilds, which rather suggests to me that the Southern Railway, and BR after them, got considerably better value out of the Bulleids than many other railways got out of other locos that attract far less opprobrium - LNWR Claughton, anyone?

Tom

 

Like 71000 was an unqualified success - not.
The Bulleids as built had their issues but were those issues only solvable by the wholesale rebuilding? We will never know for sure but there are those with engineering knowledge who say it wasn't necessary. Modifications had been made and no doubt would have continued to be made if Bulleid had continued as BR(S) CME. BR loco design had however become largely an extension of the LMS and so the die was cast.

 

In truth Bulleid did not want to build a Pacific but rather a 2-8-2 a type that impressed him greatly while working for the LNE. Regrettably he fell foul of the CCE. Now he could have produced a revised design - he had experience of 6'2" and 5'2" driver Mikado types. It was a bad time to be working on a new design, Bulleid like Gresley was very interested in the best of European locomotive design thinking, and if he had not been cut off by events then the outcome of the design process could have been very different.
If he had gone ahead with a 2-8-2, say with 5'8" driving wheels on an 18' wheelbase, slipping would not have been so much of an issue. Fit a Zara or Krause Helmholtz truck to the leading two axles and you are looking more at a vehicle that behaves more a Pacific.
A short boiler barrel can be fine so long as the guidelines on A/S ratios are followed. It was a pity that the boiler was not fully welded because that would have saved more weight and the grate area could have been reduced to 45 sq ft with little or no performance penalty. But that chain driven valve gear, to remove most of the sensitivity to axle movement the first stage should used a geared driveshaft with a telescopic section. You would need to minimise backlash in the system but there were companies in the UK that could have produced the axle mounted gearbox.
On some modern cars it is close to impossible for the owner to perform a lightbulb change - Bulleid needed to think again about that external casing.

 

On the MN's the inner firebox plates were all welded, along with the thermic syphons. I'm fairly certain that the backplate was welded to the wrapper, along with the throatplate. The latter was riveted to the barrel and the barrel strakes were riveted together, along with the butt straps. All the stiffening plates were riveted to their mating parts. The foundation ring was conventional and riveted. The stays of all types were conventionally screwed. The WC/BB's were pretty much the same although the conventional foundation ring was done away with and an inverted U trough provided, which was welded to the inner and outer firebox. 'All welded' was certainly a misnomer.

 

Martin your forgetting 30828 went main line some years ago.

 

with the greatest respect you are all missing the point!

as per my previous recent posts on this thread, the MNs exhibited the most erratic valve events regardless of whether the reverser was clamped. akin to driving a car in 4th gear and having it suddenly go from 3rd to 4th to 5th to 4th to 3rd gear without warning! this is what the BR testing of the locos discovered. neither could it be pinned down to wear in the chain driven gear. you simply cant have a mainline express loco exhibit such erratic behaviour! ron jarvis's solution was a very economical rebuild to avoid scrapping the whole class.

i dont agree with tom as the whole of the MN class were rebuilt.

always go back to the primary source information, rather than rely on secondary source books! if any one wants to PM me with their email address i will send them a PDF of the BR testing report - alas i would post it here if i knew how to!

cheers,
julian

 

... but about half the WC/BBs weren't! They nonetheless carried on presumably in productive service.

As I say, had the planned working life of steam been ca. 1980 as originally planned, I'm sure more if not all would have been rebuilt (or maybe those still in original form would have been scrapped, depending on what happened to closures of lines in the West Country, which would need to have been upgraded in order to accept the rebuilds). But steam stopped in 1967 and once that date was broadly known, the business case for further rebuilds wasn't there - which suggests the savings, while real, weren't huge: the RoI was there on a 25 year timescale, but not a 5 - 10 year one.

Tom

 

hi tom,
i think you are missing the point. the main priority was to rebuild the MNs first as they were the front line locos. the other SR classes could be cascaded after the Kent electrifrication to replace un-rebuild BB and WC pacifics, though in actual fact most continued as before - perhaps with the crews being made aware of the shortcomings of the valve gear with alterations to driving practices as a result, plus of course the imminent closure and electrification of lines these locos worked on. nevertheless the excellent work carried out by ron jarvis cant be overlooked as an excellent example of correcting at minimal cost the mechanical shortcomings of the original locos. Bulleid cant completely be criticized as apparently there wasnt enough steel in WW2 of the correct grade available to make a conventional valve gear as originally proposed - hence the chain driven gear. gear wheel driven valve gear was out for the same reasons. the unpredictable nature of the MN's performance wasnt analysed in full till 1952/4 when the culprit was located! as stated previously the results of the BR tests were quite startling and a revelation! i think up till then everyone thought the erratic performance due to oil leakage from the chain bath!

cheers,
julian

 

And 30841 briefly.

 

In various books on Bulleid there is reference to material shortages. The reference I believe related to specialist materials. Sean Day-Lewis (Bulleid - Last Giant of Steam) related that shaft and gear drive was the prefferedd option but the gears could not be sourced in 1941 but chains could

 

Then why did he design them originally without chain gear?

 

Re-read what threelinkdave wrote. The shortage wasn't steel per se, but the specialist manufacturing capacity to make gear wheels which, naturally enough, was fully committed in the aero engine industry. Because OVSB still wanted some form of fully encased drive, he had to use chains, but they weren't his prefered solution and certainly wouldn't have been the solution had there not been a war.

Tom

 

Erm OVB wanted geared drive but circumstances dictated that he couldn't so chains were substituted. How's that "pursuing an agenda?"

 

I suspect the real reason may be that he had a tendency to pick up ideas from other branches of engineering without fully digesting them. For example the late Reg Curl, who worked for him and was a fervent admirer, once told me that OVSB had an idea to utilise push on type covers for big ends a la car hub cap. On it being pointed out that the reciprocating motion would tend to shake the covers off he relented. It seemed that if a subordinate was able to give a cogent argument beyond "it will never work" in respect of an innovation he would be listened to. Perhaps those responsible for certain aspects of the design were less able to argue cogently. The sleeve valve also came from motor practice and was a perfect pain for those who had to maintain power units so equipped. Transferred to the "Leader" and multiplied in size vastly, they demonstrated all the same problems my late grandfather described so graphically about the sleeve valve Daimler. Evidently no-one asked anyone who knew the problems or didn't listen to them.

Returning to the subject of chains, when used in internal combustion engines they were a source of trouble pre-war and to an extent still are. All sorts of devices to tension these chains have been devised. Certain designers of racing engines e.g. Jano at Alfa-Romeo went to incredible lengths to avoid using them by utilising complicated gear trains. W.O. Bentley used coupled eccentrics to drive the camshaft but then he started life as a railway engineer!

PH

 

Bulleid wanted a fully enclosed valve gear and full size Walschaerts would not have fitted in the oil bath. The valve gear had to be "miniaturized" to fit and when it proved impossible to go the gear driven route, the chain driven version was developed. The only "agenda" here is the enclosing of the valve gear within the oil bath, something that wouldn't have been possible with full size Walschaerts.