The probelm is generally that the pin in the keyway slot is frozen to the shaft with rust.
I have found that PB Breaker works tremenousliy better than WD 40. PB Breaker is generally on sale at Big Lots for $1.00+ a can. I let it soak awhile then tap on the nut with a hammer, alternate holding the drive wheel upside down and right side up.
Never have had to use heat in repairing 100s of these for customers.
Mike Schneider
713 962 2681
sales@bikebug.net
Bike Bug