Man I had a heck of a time getting the lower to mate back up with the power head,dont quite know why. I could look up inside the exaust housing and see the slot for the pin and the bottom of the seal assembly,but could not get it in all the way.Finally it just went in easy.Matbe the drive shaft splines,but the shaft would not turn so I donno. I would like to know your thoughts for next time,the kids stayed up way to late because I was busy in the garage.