Whats a good book on the subject?
There are many, many books available on this and associated subjects; some are general texts, some specialize in particular aspects. A good place to start is (unsurprisingly) read through a couple of issues of the magazines mentioned; most of the publishers (Village Press, TEE, Argus/Nexus) publish and/or sell a number of texts; writing to the publishers should elicit a list of currently available books. Also try some of the suppliers catalogs found in the magazines; A.J. Reeves Ltd., Power Model Supply and Coles Power models all carry books on general topics and specialist areas such as boilers, valve gear etc.