I, too, am interested in model engineering and steam engines in
particular.  While I know of no site on this subject that is as
comprehensive as the MMD, anyone who is at all interested in steam,
locomotives, or model making in general simply _must_ visit the
excellent site created by Jan-Eric Nystrom that describes the
construction and operation of a live steam locomotive in
inch-and-a-half scale.  The site is at

  http://members.surfeu.fi/animato/steamloco.html

Jan-Eric is an animator by trade and has diverse interests.
I would invite you to also visit his main site at:

  http://www.saunalahti.fi/~animato/

John Haskey