I have learned much from Shorpy by looking up interesting items. The driver diameter question got me started on this Locomotive. Apparently this series was originally built as a compound arrangement with four cylinders. The two unseen cylinders were under the smoke box and attached to a cranked axle on the front wheels. The total rotational balance of all that equipment on the front axle determined the odd weight placement. As with almost all locomotives of this design the inner cylinders and related equipment were a maintenance nightmare, eventually having the center cylinders and equipment removed.

The A's were built as De Glehn compounds with 4 cylinders. The two hp cylinders were between the frames driving the leading coupled wheels via a crank axle. That's why the balance weight is located near the crankpin.

As for the big lumps of coal, an good fireman would use his coal pick to break them up if needed. But in my experience an engine like this will steam much better when fired with larger sized coal such as we see on 419. Put in a good bank under the door and in the back corners and they'll steam like a witch. (I've fired an NZR Ab a couple of times, and footplated A 428 at Weka Pass.)

As for mechanical stokers on steam locos, they were in use before 1909. The Pennsy were using Crawford stokers from 1905 onwards.

At any rate, it's a lovely photo of a beautiful engine and her crew.

Are there 3 locomotives in this picture?

It's curious that the counterweight on the lead driver is on the same side as the coupling rod.

No. 419 had a long life, being built in 1908 and retired in July 1961.

Some boulder-sized coal in that tender. And mechanical stokers yet to be invented. I would not want to be that fireman.

NZR is 3' 6" gauge (as opposed to 4' 8-1/2" US standard gauge), hence the relatively small driving wheels.

Those are remarkably short drivers for a Pacific, which was an extremely popular passenger engine type. Looking at the relative height of the wheels and the crewman, I don't think they can be much more than 60-inch drivers. Passenger engine drive wheels ran from 68 to as much as 80 inches.

What a beautiful early Pacific Locomotive. I have a little one in brass.