This is my SWAG (silly wild ass guess):

The bi-metallic strip keep the pin pushed down thereby keeping a valve between the viscous resevoir and the engagement chamber closed-off.

At a given temperature, the bi-metallic strip bends up (I know it this for a fact), and allows the pin to move up, letting the viscous flow.

Within the engagement chamber is a centrifugal valve that is normally closed. At the trigger RPM, the centrifugal valve opens allowing the fluid to return to the resevoir.

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What don't you understand on how we did the mod?

The little-screw just pre-bends the bi-metallic strip UP simulating it being heated.

:-) neil