The ABC is a go-to place for support, with it’s own mailing list. Nearly every airhead expert left in the world posts there. Membership is $25-50 per year (depending on where you live) and gives access to the info pages in the web site, as well as a subscription to their monthly magazine. If you subscribe to the email list, you can search the email archives here.
Robert Fleischer’s canonical airhead information website. This is a treasure trove with details on maintenance, oil chemistry, ignition timing, carb rebuilds, you name it. Unfortunately it is hard to find things unless you have spent some time poking around. Many of the articles are linked on his References Page and Technical Articles list. Some important articles are:
Anton has a ton of experience with a variety of BMWs, and shares a wealth of info in this well-organized site, for example this definitive article on oil filter installation.
Chris ran Affordable Beemer Service in New Hampshire, a well-respected shop, for a number of years, and has a bunch of instructional videos for all 1970-on beemers on YouTube. Informal, profane and informative, you can learn a lot about common maintenance procedures from him. For example, look at his video on exhaust nuts. Brilliant.
Tons of detail and videos about airhead work, repairs, disassembly, improvements, and how-to’s like:
Duane has amassed a number of articles on /2 and later Airhead maintenance, plus detailed info about various aftermarket parts and accessories. Well worth a visit.
Mostly about /5’s, some general articles about charging and batteries.