On the p85 the bolt torques down on the stationary sleeve shaft the moveable sheave, and cover slides back and forth on. The spider unit provides the contact points for the weights to push on. The bolt collar washer washer stops the moveable sheave movement. Honestly, I never have seen a clutch slam closed that hard. Actually it closes relatively soft. Maybe it would slam close by stabbing the breaks? Looks like it broke at the threaded portion of the bolt. Do they all fail at the same point? Does the bolt just need to be more robust at the thread region of the bolt? Maybe the crank PTO stub needs changed on how it holds the stationary sheave and the clutch bolt?