I should have looked closer at the teeth, but I could actually hear mine grinding on engaugement from time to time.. Maybe it was something internal in the clutch.. THe grinding sounded more like ring gear teeth, but who knows.. I think it is possible that the solenoid can move far enough to engauge the motor without the drive being completely engauged into the ring gear.. Been ages since I had one of these apart, but I believe there is a spring between the drive and the arm that moves it..
You need to cleanup the thick grease on the one way clutch splines and lubricate it with dry moly or plain graphite powder, mine did the same - even in rainy conditions, cleaned it up good dusted with graphite and moly - smooth n purrfect...
I do know that I drive torque, while listening to my friends prattle on about horsepower.
when you assembled the starter, did the bendix drive get damaged? Sometimes the shaft gets scarred and it interferes with the movement of the gear that is on the end of the starter.