Improving loco performance - re-rebuilt Merchant Navy?

I've looked at both these sites (thanks for the link) and am still confused with this one! There's a drive back from the combination lever (seems like the end of the valve rod) which goes a rocking shaft which disappears between..... But how does this give a valve movement that should be 120° out of phase?

 

I think it works like Gresley conjugated valve gear except that levers that combine the valve motion are beneath the boiler rather than in front of the cylinders. One side is linked to a 1:1 link and the other to a 2:1 link, and the two outside motions which are at 120 degrees to each other are combined to make a motion which is in the third 120 degree phase.

I doubt of you could fit that lot in under the boiler within UK loading gauge.

One other question which was mentioned in the Bulleid Pacific thread a while back; could you have conjugated valve gear on a Bulleid, in which the inside cylinder is not in the same plane as the outside two? The inside crank is not at exactly 120 deg to the other two (about 7 deg up if I remember), so would it be possible to make such a conjugated gear? Were all the cylinders of an A4 in line?

BTW I travelled behind the Australian loco 3801 a couple of years ago. It's a sort of two cylinder MN, complete with Boxspoke wheels. It went like a rocket. http://nick301.photos.us.com/p53740230.html

 

The inside cylinder on a Gresley Pacific is also inclined - at 1 in 8. This allows for unified drive which is the prefered option for a 3 cylinder design and was followed by Bullied. Thompson and Peppercorn went for divided drive but Porta wanted the A1 Trust to revert to unified - much better for the well being of the frames. Thompson was probably trying to pretend to be Chapelon when he was engaged in designing Pacifics but he appears to have understood very little about the construction methods of the Societe Alsacienne.

The conjugated gear may not appeal to everyone but it does away with the inside eccentric and properly designed gives little trouble so long as people remember to oil or grease it. When did you last see a Gresley engine fail because of the conjugated gear? Thompson had a real problem in dealing with the works of Gresley mainly because of his family links with the Raven family. He remained convinced that Sir Vincent Raven should have been awarded the CME post of the new LNER and could never come to terms with the fact that H. N. Gresley was awarded the post. The conjugated gear could give trouble if not maintained but Thompson had an interesting habit whilst CME of having Gresley engines withdrawn to the works if he heard them simply off-beat, which made him very popular with the running staff.

 

So, in reality we are talking about a conjugated gear that is before the valves/cylinders. The only advantage to this is that expansion of valve rods does not come into play. In fact, there are probably more pins and their associated clearance having an effect on valve events than in Gresley's version.

With regard to the inclination of the cylinders I would have thought that the important thing is to have the piston valves in line if you are fitting a conjugated motion and this is clearly not the case with an MN. Would it be possible to go back to an oscillating sytem, as in the original Bulleid gear but, instead of an oil bath, go for rods and grease lubricated roller bearings?

 

I've just remembered something; apparently Bulleid wanted gear driven valve gear, but there was a war on ,so they went for the chain drive. With modern technology, the Bullied Walchearts valve gear could be put back, but gear griven from the crank axle.

All this waffle about conjgated double helix backward inside upside valve gear is rather getting in the way of the fact that Bulleid sorted the valve gubins out perfectly well.

 

Easier than you think. The B17 4-6-0's had exactly that arrangement. It worked a lot better than on the pacifics.

 

I'm sorry I mentioned valve gear

Outside valve gear to inside cylinders is unusual but hardly unknown, see the LNWR 'Tishys' and also there is a large Italian 2-6-0 class.

The US 4-12-2s I had in mind had the usual Gresley gear like the Pacifics (but much bigger) when built. See here -

http://en.wikipedia.org/wiki/File:UP_9000.jpg

But later on (for the usual reasons, reduced maintenance times / costs) a few of them were altered to have a "double Walschaerts" valve gear which utilized a double return crank and second link on the right side which operated the valve for the inside cylinder. I can't find a picture of this on the Web but there is one in the Loco Profile on the UP 4-12-2's.

 

A point I've been trying to make several times to several different people fairly recently, who don't seem to want to be told that the chain-driven valve gear was the a rough and ready compromise borne from the wartime economic situation, and not Bulleid's first choice.

 

Interesting thread. I look forward to seeing what the 5 AT will do when it gets built, & find interesting the work of Wardale & his associates, many from the narrow gauge world, in fact i think the NG15 that's being restored on the WHR will incorporate more efficient exaust , roller bearings & other things.
As for cyl design on our new loco, what about looking at the Midland Paget loco? Which had 6 cyls , two on each driving axle, I think I'm correct, in 1907!