well if it is knocking and it IS a bearing, that means the bearing is Worn/Gone....so i would recommend a rebuild(Your crank will be prolly worn so a oversized bearing will come into play, if not...a new crank will be needed, especially if you're using a 6m(not weighted correctly) crank, like mine was...7m all the way:])....You can follow my instructions on my rebuild....lots of pics...ask questions too....I've learned a lot and can pretty much answer you questions, thanks to the crew here at sm...:]