Hello Jani,
Welcome. I think there is a few other Fins that use this site.
The crankshaft end has a keyway notch cut into it for a semi-circle shaped "woodruff key".The damper has a slot cut into it. Place the wooddruff key into the crank keyway,align the damper slot with it and drive the damper onto the end of the crank with a sturdy mallet or hammer until it seats. Hope this helps.
