Discussion in 'Steam Traction' started by D6332found, Jan 29, 2017.
Who could not being proud of that?
Reducing overall mechanical stresses from driving onto a single crank axle, instead dividing it between two axles. Divided drive on three cylinder engines are specific to the Thompson and Peppercorn Pacifics in this country. There are some disadvantages - the Thompson Pacifics had equal length connecting rods (largely to retain parts in the original prototypes of A2/2, but also for equal valve events) necessitating a longer front end - but largely the Thompson and Peppercorn machines did not suffer big end problems of the Gresley Pacifics or the B17s, or the crank axle problems of the P2s.
EDIT: removed an extraneous "crank" (!)
What about the LMS Patriots, Jubilees and Royal Scots, are they not divided drive?
There's only one crank axle regardless of whether an engine has divided drive.
Wasn't there the odd green loco with divided drive down west?
Those things are not mentioned in polite company ...
Sorry John, you're quite correct. I will go and correct that. It should read between axles.
I'm not an LMS man - you tell me! I presume they are from your message?
We were talking specifically 3 cylinder but yes, you're quite right.
You made the statement, not me.
I had read it was scrapped early on, but hadn't realised it was due to excessive frame cracking... I wasn't writing tongue in cheek, I think it would be a nice loco, suitably re-engineered.
I think Mr Webb's compound passenger engines of the 1880s were the first in Britain to have 3-cylinders with divided drive? The first simple-expansion would have been the GER "Decapod" 0-10-0T of 1902.
The LNER inherited Class C5 4-4-2, S1 0-8-4T and T1 4-8-0T, all of which had 3 cylinders with divided drive (the T1 differing in this respect from other ex-NER 3-cylinder types). To complete the picture, a C4 had run as a 3-cylinder divided drive simple from 1908 to 1922, but was then converted back to standard 2-cylinder form.
Britain seems to have used every permutation of drive arrangement for both 3-cylinders and 4-cylinders - drive concentrated on first coupled axle, concentrated on second coupled axle, divided drive with equal (or nearly equal) connecting rods and divided drive with unequal connecting rods. Further variety was added by the various valve gear arrangements. And for compound engines, whether to use Inside-HP/Outside-LP or Outside-HP/Inside-LP.
Should I point out that the B17s were also divided drive? Just about every 3-cylinder 4-6-0 in this country had the inside cylinder driving on the leading axle (certainly all the ones I can think of), because otherwise the crank axle means you need even more space between the centre and trailing coupled axles to get a decent size grate in, or you have the grate hanging even further over the rear axle, which tends to leave a shallow box even with a sloping grate - not good. Now equally every inside cylinder 4-4-0 had the crank axle squeezed in ahead of the grate, but the conventional 4-4-0 ran into about a 24 sq ft grate area limit, until the later ones adopted 4-6-0 style grates carried over the rear axle, but still with 10 ft coupling rods. Gresley 2-6-0s did use unified drive, but had smaller drivers, so you can play around with the wheelbase and the trailing axle is lower.
Nice photograph, that...
I haven't yet found when the frame cracking problems began - Bearing in mind this was a rebuild of the GCR's Earl Haig, was the cracking evident in its GCR days as a 4-cylinder Loco., or did it only become apparent after conversion to a 2-cylinder Loco? Presumably if a new-build was considered, the frames could be cut thicker to negate the problem, albeit at the cost of a little more weight... From what I have read, the rebuild was a a popular and smooth-riding machine. Rather nice-looking with the ex-GCR tender too.
Apologies for being wrong - but isn't that part of what a conversation is about? You knew more than me, I bow to your knowledge. LMS isn't my area of expertise. My apologies for that!
According to the LNER Encyclopedia - https://www.lner.info/locos/B/b3.php
"Only the bogie, driving wheels and the rear part of the frame were kept in the rebuild. The rebuild was too drastic, and the B3/3 regularly suffered from cracked frames. All further B3 rebuilds were cancelled." arcane tax/presentational reasons aside, I wonder this was classified a rebuild? Does anyone know if the frames it cracked the old or the new bits?
Also, FWIW, the Drummond 4-6-0s (and the double singles) were divided drive, albeit four cylinder rather than three.
I can't find any reference particularly to frame problems - for most of them, they probably didn't run high enough mileages for that to eventuate, but the final series all ran about a million miles in 35-40 years, so they can't have been too bad in that regard.
(There is a good quote in Bradley about the T14s, fairly worn out by the late 1940s but pressed into service due to loco shortages: "... the exhaust beat so irregular that instead of four equal beats per revolution there was a roar, two feeble grunts and a gasp.")
Chapelon's six cylinder 160.A1 2-12-0 had two inside HP cylinders driving the 4th coupled axle, 2 inside LP cylinders driving the 2nd coupled axle and 2 outside LP cylinders driving the 3rd coupled axle.
The B3/3 was definitely classed as a rebuild - whether it was withdrawn due to frame cracking - that's conjecture without the engine record card to hand, really, but enough sources on both sides of the Thompson debate have stated this to be the main reason so it seems reasonable to assume it has elements of truth to it.
In the event, only the front bogie, the large 6ft 9in driving wheels and the rear part of the original G.C.R. frames together with the G.C.R. axle boxes were kept in the rebuild, along with the tender (left completely unmodified). The B3/3 used the same cylinders, valve gear and boiler as the Thompson B1, thus starting the trend of reusing where possible the same Thompson era components for new locomotives and rebuilds on the LNER (see also: Thompson O1/K1/B1/L1/etc).
I had no idea the any of those had divided drive. That's amazing! All very interesting stuff.
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