Double slipper problems

[Stan]

Hello all I am after some help I have installed the double slipper option in my 501 as per instructions right shaft number of spacers 18t pulleys etc and I have the large pulley conversion belts tensioned as per instructions. The problem is I am now stripping the drive lugs off the inside of the 18t pulley to the rear diff 2 runs 2 stripped pulleys can anyone shed some light as to what I might be doing wrong

Thanks in advance
Stan