By the way - that cup is quite a tight fit into the spring. Right or wrong , when I saw the cup for the first time I thought the cup mainly serve two purposes:
1. Helps preventing dust to gather on the far end (bare part) of the pulley's mains shaft - close to the clutch Housing. The torque driver Housing slides over the bare part of the main shaft towards the clutch housing when the pulley opens at higher speed. The torque driver housing has O-rings to keep grease inside the housing, and to prevent grease seeping outwards towards to bare part of the shaft.
I thought without the cup, clutch or belt dust could gathers on the bare shaft a lot easier - and there would be a possibility that the dust could stick to the bare part of the shaft and even get trapped between the one O-ring and the main shaft. This would make it more difficult for the moving part of the pulley to move sideways.
Although the cup is not a perfect "dust seal", I think it surely helps to keep dust away from the bare part of the shaft.
2. The torque driver has a "shoulder" which slides towards the clutch housing. I thought if the cup was not in place, there would be a possibility that the spring coils might rub against the torque driver shoulder when the torque driver moves sideways. I am not sure whether this is a real possibility.
Right or wrong - I think the cup probably serves a good purpose.
