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I am struggling to remove the exhaust nut. Copious amounts of WD40 and other releasing agents have had no effect. I don’t mind wrecking the nut but I don’t want to damage the pipe or cylinder head. Helpful suggestions welcome.

Dodge

The correct exhaust nut spanner would help. Spreads the load

I don't want to spread doom and gloom, but your nut looks to be cross-threaded to me. I hope that I am wrong, but the gap between the port and the nut looks wider on one side.

Some years ago I acquired a 900 front head with the exhaust pipe still attached, which the vendor had been unable to remove. After many months of soaking in all sorts of penetrating fluids, it would not budge, and I ended up cutting the nut out with a dremel grinder. Once this was achieved the reason for the seizure was obvious - the thread had completely corroded away, probably as a result of being exposed to salt spray due to the front cylinder's
underslung location. It is a lovely low-mileage head, in great condition, but in need of a three-hundred pound repair.

Try applying some heat into the head if you haven't already.

I agree with you about the cross-threading, I had suspected as much. Do I heat the nut or the head? I don't want to damage the head. How much heat is safe to apply?

Well, you can apply quite a bit of heat to the head, remember this is the exhaust port and it gets pretty hot when the engine is running, but if the nut is cross-threaded, then you are on your own. Possibly, if you buy a proper exhaust spanner, you may be able to tighten it up again and the nut will jump back onto its correct thread, but maybe not. If it is cross-threaded and you try to undo it it will probably just seize even more. IF it is cross-threaded you may be able to gently tap the side that is sitting proud and with a punch and hammer and the thread will jump back in........But the thread in the head will probably be kaput. Maybe Eldert or Nigel may comment, who will have more knowledge.

If it's cross threaded, then the head is damaged already to some degree, maybe not catastrophically.
For the price of the exhaust nut, I would consider dremelling a slot (or two) in the nut to release it without having to try to unscrew it.
If the thread is damaged beyond use, then you have only lost the price of a (used) nut.
Consider the options given on the forum and take your pick.
Good luck!

I have had exactly this problem before.....maybe worse .....a cross threaded exhaust retaining sleeve nut and just to be sure it wouldn't come out glued in with loctite thread locker! I got it out as suggested above, had to cut the exhaust pipe off flush with the sleeve nut, used a rotary burr in a die grinder to cut the remnants of the exhaust pipe out of the way, then made three deep cuts in the brass sleeve nut to weaken it, then broke the sleeve out with a stubby punch and a big hammer . Remarkably I was able to save the port threads.....they didn't look pretty but still did the job. good luck with your one .
Cheers,
George

PS a guy I know had the same issue.......he removed the nut with a stilson plumbers wrench and a six foot extension pipe for leverage......he got the nut out, but it took all the threads in the ex port with it.

Stilson plumber's wrench is a good alternative if correct tool is not available.
The loose jaw conforms somewhat to the nut fins and spreads the load to more of them, reducing risk of them breaking.

Aye Dodge,

Same as George!

Chop the exhaust pipe as short as you can. Make at least three deep cuts into the brass sleeve nut, one of those oscillating multi-tool cutters is very good (https://www.toolstation.com/bauker-300w-multi-cutter/p54984 as you can get inside the nut to cut and weaken the exhaust pipe and the nut, using the straight blade. A small sharp cold chisel (keep it sharp) and short stubby punch with a 2lb hammer would be my weapons of choice and a good pair of Mole grips to get hold of bent bits, then twist and bend them towards the centre of the port.

Whilst Stilsons and a scaffold pole will shift these things, it takes two bodies at least to lever and to steady the whole job. The rotation of the nut, will almost inevitably damage the thread in the head. Hence the chop, batter and twist the bits method.

If you want to apply heat to the cylinder head casting and especially around the outside of the exhaust port, if you think there is any thread locking there, then a MAP X gas torch would be my recommendation. They burn HOT and need to be kept moving, but certainly cause the port area to expand.

Finger's crossed and a wee libation after the job is done for that warm glow of success!

Good health, Bill