might be telling you how to suck eggs here but the cap will only fit properly in one location, there is a tab on the inside edge which locates in a notch on the actual dizzy, turn the cap round until it cliack into position, then clip the 2 spring retaining clips on, you usually have to undos the cam belt cover t get your hand round to the bck on, unles you have girls hands in which case they may fit inbetween the cover and dizzy to reach the back clip...