Discussion in 'Steam Traction' started by GSN, May 15, 2015.
GSN will have the Hood which is how she was built.
The incident when 34067 Tangmere stalled on Hemerdon Bank was caused when her valve gear was damaged at Plymouth North Road. She had stopped on TDC and wouldn't start forwards. Not sure exactly what happened but in moving from forwards gear to reverse gear and back again the valve gear was damaged and she left Plymouth basically running on 2 cylinders. There is video of it on YouTube somewhere and she sounds very off beat as she leaves the station.
Rebuilding kept most of the original engine including the frames for both MN's and light pacifics. Main things changed was the smoke box, casing and valve gear. Minor changes were made to the frame stretchers and 35011 will need some new ones made and a few holes welded up in the frames.
" Heh! Heh! Heh! General Steam Navigation has not heard the last of meeee!"
Not forgetting the new middle cylinder.
And the middle cylinder as Std Tank has indicated. I still haven't found the article showing 34005 at Eastleigh where I had believed it had said that the 34005 that left the works had very little from the 34005 that entered but hey ho, I'm sure it will surface when I'm least expecting.
I also assume that the balance weights on the driving wheels to have been modified?
Yes a new central cylinder is on the shopping list.
The wheels will have to the balance weights that were attached during the rebuilding removed.
The major castings required to take GSN back to as she was in 1958,
New superheater header
Inside cylinder block
Front boiler mounting/ crosshead stretcher
The bottom middle stretcher that the three throw crankshaft and oil pump was mounted.
My opinion regarding the modified balance weights is why fix what not broken just to please the rivet counters as we have a big enough mountain to climb now.
Lots to do, certainly, which is presumably why no one has done it before. But I thought that removing the balance weights was required to make it run properly in original form?
I think there was no real need to modify the leading and trailing wheelsets in the first place as they were doing the same job as before.
But Jarvis wouldn't have done so unless it was necessary, surely?
I read an article from an engineer somewhere maybe on here saying they could not understand what the need for it was. But now they are fitted why introduce more stress to the wheel pans removing them.
What I understood from the video was that balance weights were fitted to counteract hammerblow, which is a product of the reciprocal forces inherent in Walshaerts valve gear, but which the original Bulleid valve gear negated, due to its use of chain drive. Therefore, with the Bulleid valve gear reinstated, would not the locomotive be out of balance if the weights remained? However, I'm not a mechanical engineer, so quite happy to be proved wrong
I am not an engineer or expert but I was given to understand it did not make a difference to the leading and trailing wheelsets which valve gear was used.
Listened to this on Friday night. Very well done, pitched exactly right (in my view) for people who are interested in the process of a restoration but a bit vague on some of the finer technical points of how steam engines work. Very engaging.
A good point, would it be less harmfull to bore big holes in them... whilst they have the wheels in CAD it might be a project to explore the effect of drilling small drainage hole in the 'pockets' around the rim - which fill up with oil, water and other muck when the loco is stood and then tip it all over the motion when moved
Interesting to see all the comments our podcast have produced, it was enjoyable recording it. To answer/clarify a couple of comments (and likely provoke more):
1. The air-smoothed casing will be representative of how the locomotive ran in the 15 years before rebuilding, so with the front cowl and smoke deflectors. The cab will likely be the modified design, though under the right circumstances we might be able to look at the original cab. We may also at some point run without the casing in front of the cylinders, if it fits the time period we're recreating.
2. The balance weights will be removed from the outside of all the driving wheels, to just leave the weights on the inside of the centre wheelset, otherwise we're going to mess with the balance of the motion, which may not help our case for grandfather rights. The weights were put there to counteract the mass of the external valve gear, so leaving them on would leave them "balancing" some phantom weights, which doesn't seem very mechanically sensible. This actually means we'll have to add weights to the inside of the centre wheelset, as the one we have currently doesn't appear to have any.
If you haven't done already, do please visit our website (www.35011gsn.co.uk), join our society, and consider donating to our project.
Dr Steve Rapley MIMechE
Chief Mechanical Engineer
35011 General Steam Navigation Locomotive Restoration Society
The balancing may have been modified when the conventional valve gear was fitted, but very little modification would have been needed for that reason. The main rotating masses that need to be balanced are the coupling and connecting rods. The return cranks and radius rods are much less massive than the connecting and coupling rods and move through smaller distances, so should need only a small change to the balancing, if you bother at all. Any major change to the balancing must have been other reasons, as ideas on that subject evolved.
Balance weights don't counteract hammerblow: they cause it, insofar as they are used to compensate for the reciprocating horizontal component of the motion of the connecting rods. The vertical component of the motion of the balance weights causes the hammer blow.
(I am likewise not a mechanical engineer but my background is in physics.)
Interesting point MellishR. My preference is to remove the weights, to return the locomotive to the condition it (or it's class members) ran in between 1953 and rebuilding. French Line I believe ran with the modified design of axle before rebuilding, and I've seen a photo from that period where no balance weight is observable on the outside of the wheels. The drawings don't seem to suggest any additional balance weights were added pre-rebuilding, so as you say, they may've been there for some other reason.
Yes, now I think about this I'm puzzled too. On line sources state that reciprocating weight wasn't balanced, which I understand, but there is still the big rotating mass of the coupling rods which can be perfectly balanced, but looking at photos it doesn't seem obvious how it was done.
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