 The outside cylinders were exchanged for the N1 type, which had been machined at the GWR's Swindon railway works following casting at Ashford to quicken construction once the N class frames were modified to accept the new design of cylinder block.This produced a robust chassis capable of supporting both sets of Walschaerts and the Holcroft conjugated valve gear.The latter was provided with grease-gun lubrication points to ease maintenance.