Haynes Manual

My primary reference for working on the bike is the 1986 Haynes manual. All six of the airhead BMWs that I've owned have been coverd by this manual. 

It is very practical, detailing what things happen to the bikes in service, how to troubleshoot faults, and suggesting workarounds for BMW special tools. Because it deals with such a long model range of bikes it has a detailed technical history, for example in describing the forks it describes at what model years forks were changed and which bikes received the new version. 

Current version extends the range, 1970 - 1996, and calls it "2-valve Twins" to distinguish it from oilheads. 

I have the BMW workshop manual as well. This is useful and I occasionally reference it, but in a practical sense I only use the Haynes version. The BMW manual is very proceduralised, focussed on disassembly, check/replace, and reassembly. It relies on a lot of special tools many of which could only be affordable to a dealer.