Did this happen before you removed the engine as well? or did it just start after the reinstall?
maybe the clutch air gap is closed up. You see the 3 spring loaded studs with 9/16 headed nuts. You can adjust those so you have .015-.025 air gap between the clutch disks. Also make sure all the pulleys, keyways, washers and clutch are all on in the correct order and not overtorqued.
if all that seems right, gotta be a bad clutch.