Several _HR_ wagons were used as locomotive engine block transports. The engine blocks were generally removed from locomotives at South Dynon and transferred to Newport Workshops for overhaul.
In 1985/86 the two remaining HR engine block transports were recoded and renumbered to the HZE class.
HR 12 (2nd) became HZE 230 and HR 15 (2nd) became HZE 231.
HZE 230 was out of service by 1990.