you have to use your eye when your near the "seated" area of the mech seal. the seal will not go in any further then the specified seating area, if it doesit will not seal right and you will probably break the seal if you try it.

usually the new mech seals are tighter when first installed and once they break in they free up.

you put the washers in between the old seal and impeller correct? any other way will damage the seal