 Certain engines also suffered from reliability concerns, which later led to trial modifications made to DS 7 (WF 434) by shortening the smokebox by 520mm and fitting a narrower 'Master Mechanics' funnel.This modification was successful, but despite the order to equip more engines with this modification, DS 7 remained the sole engine with this alteration.The first four locomotives were identifiable from the later four by several distinguishing features