The speedometer on a bike is a very important item. You need one for a number of reasons, most of which are related to keeping your licence, but it also tells you how far you've travelled and possibly how far the previous owners have been on your bike as well.

Lots of bad things can happen to speedos, sitting out at the front of the bike all exposed. It's also not obvious how to take one apart when stuff goes wrong, so here's how to do it.