One of the most important tools you can own, if you're going to do your own dirt bike maintenance and repairs, is a manual. A good shop manual gives you step-by-step instructions for just about anything you'll ever have to do on your dirt bike – whether you're a weekend trail rider or a serious motocross competitor.
One of the things I like most about my manuals is the exploded parts diagrams. These are invaluable when disassembling and reassembling parts.
But sometimes you can't get access to a manual for your dirt bike, or you're doing a repair on a friend's dirt bike. In that case, you can still get hold of a parts diagram. One of my favorite sites to get these is Mr Cycles .
They have great diagrams for most dirt bikes, including Honda, Suzuki, Yamaha,and Kawasaki.