I fully understand the taper and friction thing, and i'm assuming, you mean the crankshaft chain sprocket install, however, the sprocket is keyed - same with the alternator rotor - it's keyed. not trying to argue the point, but the original question was referring to the (keyed) rotor install. somewhat of a noob, and trying to jog my memory, but the way i'm looking at it, the chain sprocket needs to fully seated in position and it's keyed to prevent rotation. once installed, you shim the clutch sprocket so the two are in alignment. the taper is there, IN MY OPINION, so the sprocket can only install one way, and to be fully seated, as a starting point for sprocket alignment purposes, and has less to do with a friction fit to prevent rotation. while I did install mine assembly dry, I still say a very light coating grease shouldn't hurt anything. again, not trying to argue the point - just my 2-cents FWIW. peace....