The history of the 433E is in direct parallel to that of 344F 4-6-2. The derailing tendency of the back bogies and the clogged-up ashpans needed a more drastic solution. Crews also complained that the big smoke deflectors obstructed the view forward. Thus the remaining 433Cs and 433CCs were included in the rebuilding programme that Tešlov instituted on his return after the Second World War. Tešlov retired before much more than draughting and pattern-making had been done and the work was completed by his able successor, to whom the design is also attributed. Rodnivacek augmented his chief's concept, which included Houlet superheaters, bar frames and roller bearings, with boxpok wheels, high running plates and improved suspension. In the final analysis, not much was left of the original engines. A total of 14 locomotives were rebuilt, some of the work being contracted out to Henschel and making a useful contribution to the RSR's fast goods motive power stud. Some locos ran for a number of years with Vanderbilt tenders, as shown below.

 

In the austere years following the Second World War, the RSR was looking for ways to improve the power and efficiency of its engines at minimum cost. The poppet valves used on a small number of LMS "Black Fives" seemed promising and were applied to six 344Es in 1951. Comparative trials showed much improved performance and reduced coal and water consumption but also higher maintenance costs. Rodnivacek was convinced that through good detail design the poppet valves could be made sufficiently robust and trouble-free for general application. And so it was. All engines of class 433E received poppet valves to become class 433EE, conversion being completed by the end of 1954. Vanderbilt tenders were also applied to the entire class.