 Problems with the class were experienced immediately , with the first 25 locomotives being withdrawn in October 1951 after several complaints were received from crews regarding the driving wheels shifting on their axles . They were subsequently modified , and released back into revenue @-@ earning service . Initially the return cranks on the main driving wheels were of LNER block type , as seen on Arthur Peppercorn 's A1s and A2s , but this was changed to the simpler LMS four @-@ stud fitting . This was the result of a problem of overheating bearings within the cranks , and difficulty in removing the LNER @-@ type casings . <unk> – <unk> were built with roller bearings on the leading and trailing coupled axles only and plain bearings on the remaining axles , whilst <unk> – <unk> were built with plain bearings throughout . However throughout their service the roller bearings used in remaining cases showed no advantage in reliability or cost . 
