Simple Question (I think)

[Swivelhart]

What keeps the bearing race from turning on the prop shaft at the front of the lower unit? Another words a car has a down ward force that keeps the race moving the rollers of the bearing but on a prop the force is foward. Without the downward force what keeps the shaft from turning inside the inner bearing race. Am I making sense. I ask because when I took my shaft out it looked as though there was slight discoloration from perhaps getting hot i.e turning inside the race.

Here is a picture of the shaft after removal with the discoloration indicated.

It is not quite as dark though when compared to this picture where you can see both ends.