Reddit mentions of Motorcycle Basics Techbook (Haynes Manuals)

This website is a decent starting point:

http://www.dansmc.com/mc_repaircourse.htm

This book might help as well:

Motorcycle Basics Techbook (Haynes Manuals)

Motorcycle Basics Techbook. Covers all the major systems in detail and how they developed.

Read.
You can start off with this:
http://www.amazon.com/Motorcycle-Basics-Techbook-Haynes-Manuals/dp/185960515X/ref=sr_1_1?ie=UTF8&qid=1333517762&sr=8-1

Here's a website with a lot of good stuff:
http://www.dansmc.com/mc_repaircourse.htm

If you're going to buy a used bike, here is a great source of information for doing an inspection:
http://www.clarity.net/~adam/buying-bike.html

When you narrow your selection of bikes down to a few models, look around for internet forums that relate to those. You'll get an idea on how much online support you'll be able to find, maybe people with the same bike that live in the same city, and you can familiarize yourself with problems common to that model. That's going to help you decide how much someone's "pride and joy" is actually worth to you.

When you buy the bike, go out and buy the shop manual for it as soon as possible.

Google everything else.

https://www.amazon.com/Motorcycle-Basics-Techbook-Haynes-Manuals/dp/185960515X not sure if that would help but seems like it gives a basic rundown of common engines. Looks like something you might be looking for at least for now

YouTube is a great resource, as people are saying. Especially if you can find someone who is working on a similar bike.

The basic user maintenance for your bike will be briefly described in the owner's manual. To go deeper than that definitely pick up the Haynes or Clymer service manual for your bike. They are more beginner-friendly than the manufacturer's service manual.

Finally, if you really want to foster a deep understanding of how motorcycles work on a book-learnin' level, grab the Motorcycle Basics Techbook https://www.amazon.com/dp/185960515X