[john walker's workshop]

never heard of anyone actually boring out 911 guides to sleeve them. as far as the seat being off from the center of the new guide, that's caused by the worn guide allowing the valve to wear one side of the seat away. when new, they closed precisely on the seat. when the guide and valve stem wears so the valve is sloppy in the guide, the rocker action will push the valve a bit sideways and when it closes, it contacts the seat on the side toward the center of the combustion chamber and basically drags itself in. so when the new guide is installed and you begin to grind the seat, it won't clean by as much as 1/2 way around for a while. 3.2s are the worst for some reason. even if you could sleeve the guide, you can't compensate for seat wear. the guide would have to be bored on an angle.