Source text and photo: http://www.aqpl43.dsl.pipex.com/MUSEUM/LOCOLOCO/steamotor/steamotor.htm#221
Link broken since: February 2020.
[Classication = Group 2]
“The simple (non-compound) V12 motor was described as “Type Dabeg” and appears to have relied entirely on altering the cut-off for control.
The valves were desmodromic, ie with positive opening and closing rather than relying on springs for closing, as with modern IC engines.”
This appears to be the only photo in existence.