It is my understanding that Mr. Bulleid originally wanted to apply poppet valve gear to the Merchant Navy locos, but was prohibited because of the lack of certain supplies during the war. Has there been any conversation about how these locos would have performed if the poppet valves could have been installed?
Can you give more intel about this maybe photos?
General Steam Navigation locomotive is being restored.
General Steam Navigation Locomotive Restoration Society
David
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Thanks David, That helps a lot!
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Bulleid was, I thought, fairly opposed to the idea of poppet valves. He certainly went a bit overboard avoiding them in designing the āultimateā steam-distribution system on Hartland Point and the Leader engines, and when he revisited the Leader idea at Inchicore, at smaller scale, he used piston valves.
If you wanted a āscience projectā for a Merchant Navy, look at using paired valves for intake and exhaust, and drive them by a method that does not develop lost motion in the way the Morse-chain version so lamentably did. I would add that almost all the oil follies on the MN had to do with sheet-metal reservoirs and covers, and use of modern plastics and elastomers might have solved it.
Turning back to Leader, the sleeve valves offered perhaps the most ideal combination of large port opening, short dead volume, and accelerated action that could be achieved mechanically in a reciprocating engine. I cannot fault Bulleidās use of Meehanite (which, amusingly, was proofreader- corrected to āmechaniteā in one of the books) for the very thin sleeves, but oh brother! there were a lot of hard-to-seal rings, and multipoint Detroit-style lubricators for them all, with full superheated-steam temperature cycling to many of them, and the steam leaked and leaked and leaked to where you had to ask where the big savings over piston valves was supposed to be.
Wardale doesnāt care for poppets either, nor particularly for Cossart-style drop valves (which is sort of an attempt to have your cake and eat it too with cam-actuated valves). He developed the steam-cooled articulated valve with ādiesel-styleā thin rings that I think would be the ābest-practiceā thing to fit to General Steam Navigation.
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The books that I have been reading about the Merchant Navy & West Country locos note that Bulleid intended to use poppet valves on these locos only to be denied by wartime needs for certain metals.
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Although I live in the UK., sorry I cannot answer the question. The Southern Railway is the least of my interests in railways.
David
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You laugh my friend, but the Southern are the least interesting railway company to me.
Northern and Scottish companies are far more interesting. 
David
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I suppose.
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Yāall seem to be confusing Bulleidās experience starting in the late '20s (under Gresley) with his preferences as CME of the Southern after 1937. He had become well aware of the issues with Lentz gear by the early Thirties, including the absence of ābetter fuel and water rateā in normal running. His paper to the ILE in 1929 was before the rash of failures in the LNER classes that were fitted, and the comparative trials of Mikes 2001 and 2002.
The original āgreat advantageā in the mid-Twenties was the nominal ability to run far higher superheat than conventionally-lubricated piston valves would tolerate. The ādocumentedā metallurgical issue was with the point-to-line contact of the followers on the continuous-contour cam ā a concern that would be re-seen on Franklin type C in the late Forties.
Bulleidās patents for chain-driven valve gear show nothing but piston valves. Southern never (to my knowledge) built any engine with poppet valves, with or without āwartime metallurgical restrictionsā. Iād think Bulleid by 1943 would concur with Shields: āEveryone was interested in the poppet gears, but they did not seem to have got as far as they should. They were certainly attractive, but there seemed to be something about them which prevented them making progress; what it was he did not pretend to know.ā
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In the 21st Century there are rarely NEW ideas in terrestrial transportation. There are many 20th Century ideas that have come to successful fruition because metallurgy and other technologies have caught up to make the idea a success.
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Yet the question still remainsā¦
ā¦not just performance wise, but also maintenance wise. Of course there would not have been the problems with misplaced oil and maybe not the problem with ācreepingā valve settings.
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Itās an interesting question.
I see no reason, other than ālateness of the hourā, why British Caprotti (as on Duke of Gloucester 71000) could not have been used. This solved the bounce and cracking concerns with spring, return poppet valves by using steam pressure to hold them closed against cam action.
If the Merchant Navy class was to retain zero overbalance, care would have to be taken with outside cranks to drive the cambox. I donāt really see any more issue than was introduced when conventional valve gear was installed on the rebuilds.
The concern would have remained cutoff control. Performance would have been ghastly with stepped cams, and Bulleid had had first-hand experience with continuous-contour cams in the early Thirties and would have been aware of what would be necessary to remediate the concern. Similarly, I canāt help but think he knew his cast-irons and would have recognized how to address the thermal cracking problem from excessively high superheat during high-speed operation (which was one of the great problems with the poppet valves Gresley specified). I have no real idea how useful the Lentz technical people would have been in specifying a poppet valvetrain for the class.
The big problem with the chain drive was that it reversed under load, so any slack or wear threw the valve events off. A chain drive to a poppet-gear cambox would run unidirectionally, so adjusting for wear would be a (more or less) static adjustment at periodic maintenance. However, reverse would be another issue, even though the cam could have dedicated āreverse lobesā ā perhaps a Weller roller tensioner would have worked, but I can see āissuesā even though sloppy events would be much less concern in reverse.
The oil-bath problems were down to lousy thin sheet-metal and incompetent gasketing. There should be little problem building a ballastproof chain case. However, I do think return-crank gearbox cam drive would have been ābetterā, with inside gear drive an alternative.
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