I was trying to remove a really stubborn nut on a lawnmower pulley. After a half hour with a grinder, I only made a dent. I found a simple trick that allowed me to easily break the nut.
The bottom of the mandrel was stripped. This prevented me from using the blade to stop the pulley and break the nut free. After trying unsuccessfully to cut the nut with a grinder, I took another approach.
I have a chain wrench in my plumbing tools. It is essentially a handle with a length of chain that can be wrapped around a pipe or nut. I was fortunate enough that it was large enough to wrap around the pulley.
I used a breaker bar with a pipe extension. In other words, there was a huge amount of torque. I was able to wedge the chain wrench against the cutting deck. I had been dousing the nut with penetrating oil.
With a little effort the nut broke free. Keep in mind that the chain MIGHT scratch the pulley. That can be sanded out or smoothed with a stone. Or, you can replace the pulley.
