micka,
On most engine shafts the best way to remove the blade plate boss is as follows:
1. Clean the crankshaft with emery paper towards the engine.
2. After cleaning and the shaft is shiny, you then tap the boss towards the engine.
3. Once you have done that then remove the key in the shaft.
4. Then clean the shaft with emery paper till it is shiny.
5. Remove the boss and then remove the seal.
Also use some WD40 before you remove the boss (after cleaning).
