I'm not looking at one this minute but I'd bet the "little pin" is the end of the tensioning spring.. I'd also bet you arn't pretensioning the belt while installing it.. How did you get the belt off in the first place? Did you insert a wrench and back off on the tension?
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

professional bovine relocation specialist