The following is an extract from ‘London Midland Fireman’ by M.F. Higson
The numerous Class 4F o-6-o goods was a much more controversial locomotive. This no doubt was due to its Derby characteristics, which were not appreciated very much by the older generation of LNWR and LYR division men. My experience indicated that, on the whole, the older MR engines and Derby-built locomotives were better steamers and freer runners than those from Horwich or Crewe works, the 45XX series being the most temperamental for steam. The best examples in the class were the few with tall chimneys (indicated by a blue circle on the cab sides) and they usually steamed very well indeed. The older MR engines were almost all shopped at Derby, and some drivers insisted that Derby set the valves differently from Crewe and Horwich. This may indeed be so, because I cannot believe that Derby supplied each 4F with a guardian angel or used any other magical persuasion!
Some of the MR engines and others boasted a Derby-type exhaust injector of the same type as that fitted to the compounds, the Fowler 2-6-4 tanks and, I believe, the ‘Crab’ 2-6-0s. These injectors were not very strong and gave frequent trouble, the usual footplate practice being to rely on the live-steam injector only. Some of the MR engines had the old chain-and-flap type of firehole door, a very awkward piece of equipment which was not easy to open and close in a hurry. With this type, the main door fell horizontally away from the hole, sometimes at the most inconvenient moments. It worked in conjunction with a flap at the top edge to regulate the admission of air. This ungainly piece of equipment was not very helpful when the engine was at all shy for steam, being either open or shut and not making for quick firing, as over a half-flap. The hinge frequently became jammed with small coal,requiring the flap to be flicked up and down to remove the obstructions.
All 4Fs had two features in common, a gap between the floor and the firebox back-plate which caused clouds of dust to swirl up when the engine was moving, despite wedges of sacks and old clothing stuffed in to block this space, and a roof gutter which deflected the rain in a stream down one’s neck or back. However, comfort was of secondary importance on the 4F, for the art of keeping going was generally a full-time occupation.
Personally I learned to treat the 4F with the greatest of respect. If circumstances allowed,I built the fire up very carefully, mainly under the door, and kept firing at frequent intervals, about four shovels full at a time. Firing too heavily only caused the firebox to choke with smoke and a heavy black fug to roll out of the chimney while steam pressure fell rapidly. The grate was so inclined that coal needed do no more than just get inside the door, with a little placed down each side. At best, the fire could be so thin at the front as to be literally hopping about on the grate, bur this was hard to achieve, and with poor coal the front of the grate soon became clogged with dirt and steaming became much impaired.
The parallel boilers of these engines seemed more susceptible to dirt and priming than did taper boilers – this goes for all MR-type parallel boilers and the method of boiler feed delivery was more cooling than top feed. The ancillary fittings blower, steam heat supply and injectors were a great drain on the boiler and working a passenger train with a 4F 0-6-0 was quite an experience. They rode quite well, however, and MR men usually adored them, defending them at every stage. Other men put up with them or despised them, and LNW men much preferred their 0-8-0s. All in all, the 4F was a most controversial engine, which personally I found to be too temperamental and unreliable.