hi there where all D261/334 rebuilt ito z16 ? and whats the main difference between this and the D255 (Z15)
The D261 and D334 classes were reclassified as Z16. The rebuilding occurred under the original classification.
The Z16 class had cylinders one inch larger in diameter than the Z15 class and were allowed greater loads.
That is why there were two classes in the 1924 system.
The D334 had a conventional leading bogie rather than a two axle bissel pivoted near the leading axle.
There were variations in the shape of the smokeboxes within the D261 and D334 classes.
But the reason for splitting into two classes was the cylinder diameter.