Nimbus - Technical Development 1934 to 1959
In English - Hardback
This is the world famous book written by the Nimbus expert in Denmark - Knud Jorgensen. Now in English.
Covers all the technical aspects you will ever need to know - and sheds light on some of the more obscure changes and improvements.
This is not a maintenance manual as such - but has a lot of technical info not mentioned in some manuals.