There is a backyard method of removing the nut, which caused no drama, but you still need a tool to replace it.
Remove the spark plug so that the motor spins freely, place a well fitting socket on the nut and use a long breaker bar.
Place a lump of something hard to the right of the flywheel where the end of the breaker bar will foul it.
Swing the breaker bar quickly in a clockwise direction until the bar fouls the hard lump.
The bar will stop abruptly but the flywheel will want to continue to turn, resulting in the nut backing off due to rotational forces.
You may need a couple of swings.
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There is another way which I have not used, and do not recommend.
Take the spark plug out and revolve the motor until the motor is at TDC this can be checked by feeling the piston with a bit of plastic fuel line.
Now rotate the motor in a clockwise direction about 30deg, this will bring the piston about a 1/3 way down the bore.
Feed as much poly rope down the spark plug hole that you can get to fit in.
When you now try to remove the nut the piston will try to compress the rope and become firm, stopping the motor revolving.
This method can be used to replace the nut, but of course the process must be done in reverse.
I do not like this method because I fear that it can stress the connection rod, and also if the piston goes further down the bore, lumps of rope can be pinched off if they enter an uncovered port, and the last thing you want is a lump of rope lurking in a port.