I'm thinking your impacts don't have enough torque. If they did, it would have come out or broke the bolt by now.

to get some heat into that crank,,drain the oil and rev to 6k for 2 minutes or until it stops.bolt will come right out.

and yes,,its a joke
I second the 18v fuel

I'm amazed you have not been successful. Bigger air impact. It has to have mechanical damage to the threads at this point, even red loctite would have been taken care of by now. Any NASCAR teams nearby? I have a modified IR pit stop gun that will produce 1000ftlbs of torque at 100PSI, and sounds awesome!

Popped up on my FB news feed; almost like they know me:

I like the idea of a tuned up impact. The IR was my first impact wrench I owned and still have to date. I also forgot I had bought another one that was in another tool box I rarely use. In addition to those two air I also found one more our mechanic uses at the golf course shop. I’m going to turn up my air today from 145 to 175. And also plumb a hose directly to the tank. Honestly my cordless sure feel and sound more pissssed than the air.

What brand of cordless? M18 fuel in my experience seems like it'd bust anything.
Another thing if you're going to knock at it with an air impact gun again, spray or drip some oil or lube into it before ya try. Seems to give them some extra oomph IME.

On way back from race track. Borrowed a friends modified snap on air impact. He said it outworks his cordless. For sure on the oil. My 18 volt cordless have raised havoc with a lot of bolts. I most generally don’t need anything more than my 14 volt 3/8. Gonna raise the psi
on the compressor and give this one a shot at it.

I wonder if you welded the same size nut on the nut the heat from the weld would penetrate better the the torch.

I have a 1/2” 18v Milwaukee Fuel impact in Manistee I’d let you borrow to try, it hits pretty hard

No kidding!!! I’m just up in Onekama. SE end of portage lake. I would like to give it a try. Turns out the revved up air impact I tried from the track didn’t brake it lose but did have a noticeable set of balls.

Heading out looking for mushrooms now but will be in the area all day.

Tks
John