Got a 91 sportster that one day started knocking real bad like it was between gears. It's all tore apart and without final drive or clutch put in you can spin the main drive gear and hear a knock like gears bouncing off each other. I've tried everything I can think of and it's hard to see what it's doing while in there but almost like the 5th gear on main drive is making contact and it shouldn't be. Also even while I am in neutral I turn the main drive I cannot stop the main shaft from rotating . Possibly bearings??? Need help can't afford to do to much guessing. Thank you

 

You say its all apart?
Have you pulled the trap door?