All the stuff that keeps you pedalling.

Drivechain fettling

This is definitely not manufacturer approved! The bearing cups on a Shimano XT Hollowtech II bottom bracket have "DO NOT DISASSEMBLE" written on them. Why? I don't know? Probably because they want you to buy a whole new set of cups for 30 quid or so instead of a couple of the standard bearings they hide for a fiver or so (try your local bearing supplier or eBay)?

If you want to ignore Shimano's instructions? Here's how. This is done on an XT setup but others are similar. Obviously I doubt any warranty would be honoured if you do this? You proceed at your own risk!