▁where ▁they ▁were ▁intended ▁to ▁work . ▁It ▁took ▁nearly ▁a ▁year ▁to ▁carry ▁out ▁the ▁programme ▁of ▁track ▁and ▁bridge ▁strength ening ▁and ▁some ▁of ▁the ▁new ▁locomot ives ▁ended ▁up ▁being ▁held ▁in ▁st aging ▁for ▁all ▁that ▁time ▁before ▁the ▁Chief ▁Civil ▁Engine er ▁would ▁allow ▁them ▁to ▁run . ▁ ▁When ▁introduced , ▁these ▁engines ▁were ▁up ▁to ▁date ▁with ▁contemporary ▁locomot ive ▁practice . ▁They ▁were ▁super he ated , ▁with ▁Bel pa ire ▁fire box es . ▁The ▁cyl ind ers ▁were ▁arranged ▁outside ▁the ▁plate ▁frames , ▁with ▁the ▁ ▁diameter ▁outside ▁ad mission ▁p ist on ▁val ves ▁arranged ▁above ▁the ▁cyl ind ers ▁and ▁actu ated ▁by ▁Wal sch a ert s ▁val ve ▁g ear . ▁The ▁drivers ▁and ▁intermediate ▁couple d ▁whe els ▁were ▁fl ang eless . ▁The ▁motion , ▁ax le box es ▁and ▁several ▁other ▁details ▁were ▁identical ▁or ▁similar ▁to ▁equivalent ▁parts ▁of ▁the ▁Class ▁ 1 0 , ▁which ▁was ▁built ▁at ▁the ▁same ▁time ▁by ▁the ▁same ▁manufact urer , ▁and ▁their ▁Type ▁X M 2 ▁two - ax le ▁bog ie ▁tend ers ▁were ▁identical . ▁ ▁The ▁load - b ear ing ▁spr ings ▁of ▁the ▁trailing ▁b iss el ▁consisted ▁of ▁single ▁hel ical ▁spr ings ▁of ▁round ▁section . ▁Since ▁the ▁single ▁spring ▁would ▁not ▁stand ▁up ▁to ▁the ▁load , ▁it ▁was ▁soon ▁replaced ▁by ▁a ▁double ▁spring . ▁L amin ated ▁spr ings ▁were ▁subsequently ▁fitted . ▁A part ▁from