Have 2012 road king went to start bike and the starter just spins. U can feel it kick out on the primary side and hear it spin but not engage to turn bike over. Removed starter and replaced guts with new pieces all but the gear and shaft bike still won't start starter just spins.

Take the side cover off the engine, to hold the drive in position to mate the starter. For example, my CB450's starter has a spline on the output, and the sprocket that mates it will drop down inside the case when the starter is pulled.

Not sure how that one engages. Had an 1100 Magna that used a starter clutch, it used 3 rolling pins in a housing, The housing was cracked and would allow starter to engage engine. Replaced housing solved the problem. Not sure how yours engages? Good Luck