i have just had the same problem on my Techno, ensure all surfaces are completly smooth and no sign of the woodruff key picking up on the crank or flywheel, try fitting the flywheel onto the crank without the key in first and check you get a good fit you should have to use the puller to break the seal if it is seating ok then fit your key ensuring it is parallel to the slot.
the flywheel should be torqued to 14 KGM good luck