There is a factory seal that goes onto the steering stem first to seal the lower bearing. The aftermarket tapered bearings I have come with a seal also, but I can't remember whether I use it or the oem one. If I remember correctly there is a dimensional issue depending on the stack of components. If the lower inner race is too close to the lower tree, the tree will contact the frame before the bearing is seated properly. If the race is too far from the tree due to the seal being too thick, the stem will not project through the neck far enough and tensioning nut will not engage all the threads - which is nearly the case no matter what as the tapered bearings are thicker than the ball bearings they replace. I can't remember what the best solution is, but install the lower outer race first and make sure it is completely seated in the steering neck. Then take the inner and place it into the outer shell and measure the difference between the height of the bearing face and the steering neck. You want to end up with the lower tree as close to the neck as possible without touching so the stem will project out the top as far as possible. I can't remember what the best seal/shim combo is best, but do recall having to remove the new inner race from the stem to make changes which is sometime difficult as it is an interference fit. Otherwise, as Clem has said, the upper race will stand proud of the neck. I do seem to remember not being able to use a top seal as there is not enough space. There is no correct torque, and again Clem's direction is fine. I generally over tighten tapered bearings a bit to squeeze the grease from between the elements and then back off until the assembly moves freely. There is very little load on the steering of a bike, so the compression of the assembly can be very loose as long as there is no play. Most applications should be tighter, like the front wheel bearings of a car or transmission shafts because the loads are much higher and more compression is needed to make up for the resulting distortion.
