I saw video, and it was not great quality, and the train was a long distance away. It appeared to me that one set of drivers had six, while the other had four. It was an N&W loco. Could I have seen that correctly?
Still in training.
Norfolk & Western Z Class Locomotives were 2-6-6-2 articulateds. They had 190 of the model. On some railroads they were called Mallet Moguls.
At this website there is a broadside view of a Class Z if you scroll down.
In the picture, if you look closely the first driver on the front locomotive can be seen, almost hiden, though, behind the crosshead guides, the piston, and the gear just behind the front cylinders.
https://www.american-rails.com/z.html
In terms of "asymmetrical" drive, Great Northern had 2-6-8-0 locomotives.
Santa Fe had some 4-4-6-2 Mallet passenger locomotives for a whiile in the early 1900s.
The Pennsylvania Railroad had a class Q2 of 4-4-6-4 rigid frame freight locomotives.
There are a couple of pictures of a Q2 on this page.
https://en.wikipedia.org/wiki/Pennsylvania_Railroad_class_Q2
It must have been a Z or an A class, and I just couldn't make out the one wheel pair as it was hidden by the crosshead, etc. Thanks.
The only other mainline articulated with a four-coupled forward engine was a B&O experiment (on one of the two first true high-speed simple articulateds). These locomotives came from Baldwin as 2-6-6-2s, which was not particularly advisable for engines that size at high speed, and B&O tried putting a four-wheel lead truck on for better stability (resulting in the elimination of one driver pair to make room)
I have tried for decades to get test information on this, but the upshot historically is (1) the engine did not run in this configuration for very long; and (2) B&O never repeated the experiment, and no one else in North America did, either, even though the subsequent history of high-speed articulateds, both 2-6-6-4/6s and Challengers, is remarkable.
(The PRR Q2s were rigid-frame engines, which eliminates the great cause of instability from a hinged four-coupled engine. Interestingly their rigid wheelbase is shorter than that of a 5001-and-up-class ATSF 2-10-4, which no one argues wasn't a high-speed locomotive...
NOTE: There were four-coupled main-line Garratts... very good, very fast, eight-cylinder Garratts. This discussion is about Mallet-style articulation, though.
Why is the word in the title 'consolidated' and not 'articulated'?
Yeah those Z's had massive cylinders. I can see how easy it would be for a set of drivers to hide behind them at the right viewing angle.
Same me, different spelling!
In a true "Mallet" using double expansion, the high-pressure steam is first used in the rear cylinders, then the low-pressure (but still powerful) steam is exhausted to the front low-pressure cylinders, then exhausted up the stack. To use the low-pressure steam properly, the front cylinders had to be huge compared to the rear ones.
In a "simple" articulated, all four cylinders get high-pressure steam directly, so all four are the smaller size.
They look large because the Z's had a smaller well, just about everything, at least when compared with the later Y class compounds. Without looking up the information, I'd guess both classes had similar sized front cylinders. At least referring to the Z1b and late Y5. The original Z1's of course had slide valve steam chests on the front engine truck and piston-valve cylinders in the rear.
There is a compound articulated locomotive with a four-coupled leading engine. How could you overlook Deep River Logging 7, Skookum? It is currently active on the West Coast.
Does have to be said it has the look and the poise of a mainline rather than a logging engine...
https://static.wikia.nocookie.net/locomotive/images/5/59/Skookum_3.jpg/revision/latest?cb=20190607084329
It does not have a 3-coupled rear engine as noted in the OP, but it is a 2-4-4-2 for sure.
https://www.railpictures.net/photo/734626/
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