The best books available are probably the ICS (International Correspondence School) courses. Back in the day, one could take a correspondence course to become an engineman. The smaller "blue" books will have the most "current" (i.e., 1940s) information, although the red and green bound volumes from earlier in the century are good too.
You can pick these up for about $15 bucks a volume for originals. "Locomotive Management" is good, and so is "Hand Firing of Locomotives," (the link is to a reprint on Ebay, but it shows the table of contents, so you can get a pretty good idea of what you're getting), but there are many volumes, covering everything from brake systems to steam locomotive appliances to generators to boilers. Basically everything. Check out www.abebooks.com for other volumes. This one's a reprint, but for 23 bucks, you can't go wrong.
You might be able to get them on CD here. He includes a partial list of the volumes:
Vol 501 | Locomotive Boilers |
Vol 503B | Locomotive Valves and Valve Gear |
Vol 504C | Walschaert and Baker Valve Gear |
Vol 505C | Locomotive Valve Settings |
Vol 506 | Firing of Locomotives |
Vol 507B | Locomotive Stokers |
Vol 508D | Locomotive Boiler Feeding Devices |
Vol 510C | Locomotive Management |
Vol 514B | Compressors and Brake Equipment |
Vol 515D | Number 6 and Number 8 ET Brake Equipment |
Vol 516B | Air Brake Troubles - Brake Rigging |
Vol 519 | Automatic Control Equipment |
Vol 530 | Automatic Train Control |
Vol 598 | Freight-Car Brake Equipment |
Charles McShanes "Locomotive Up To Date" will give you some good info.
Angus Sinclair's "Locomotive Engine Running and Management" is widely considered a classic in the field, not only for its information, but his great writing style.
Finally, here is a great page with all kinds of information available, including a complete list of the ICS courses (about 1/3 the way down)