If you are talking about what I think you are talking about, I think you have to tear the whole engine town, crack the case and pull out the old shaft (rod) and replace it. Then reassemble the whole motor. Or if your lucky it can be done by just pulling off both engine side covers I cant remember. But once your in there all you need to do is remove one circlip to take out the shaft (rod). All I know for sure is the circlip is on one side, then the rod is simply pulled out the other side.