Reviving an old thread. I have the same problem. I blocked the blade with a wooden block but when I try to break the nut loose, the spindle turns along with the pulley above the deck... I've sprayed with PB blaster, waiting for it to hopefully break the rust while I am writing this. I see no flat side on the spindle so that I could hold it in place with a wrench and stop it from spinning (as some circular saws have). The spindle has another nut at the opposite end (on top, on the other side of the deck) so I could use a wrench on that but there is a chance that the top nut (holding the pulley) will break loose instead of the blade side nut.
It is a Murray Select riding mower with a 42" deck (16.5HP). I bought it used and I don't have the manual for it. I would love to check if the nuts are fastened clockwise or counter clockwise but the tag under the seat is so faded that I can't make out the model number.
Does anyone have this information?
Any input is appreciated. Thank you!