Maybe this will help.
Once the outer cover is in place the head of the crank mounting bolt is trapped between the inside of the crank arm and the cover. If you tighten the bolt it pushes the crank onto the spindle. If you loosen the bolt, it backs off crosses the space until it's pressing against the cover. Now as you continue to loosen the bolt, it presses the cover and jacks the crank arm off the spindle.
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