Had to change the H/G over the last few days. I marked the cam belt and the two cam sprockets before removal. Just come to replace everything. I keep lining the two sprockets up and the notch on the crank ( I'm certain in how these line up), but when I come to rotate the crank to tension the belt, the marks keep coming up 1 tooth out. I've tried every way I can think of to sort this. I've tried putting the belt on 1 tooth ahead, I've tried taking the slack out of the front of the belt by putting the sprockets slightly ahead, nothing seems to work HELPPP.