• IMHO, you are focused on the symptom and not the cause. Unless you look for the root cause you'll be doing this again next year. The most likely problem is that the nuts weren't installed with Never Seize compound. Exhaust nuts, spark plugs and mufflers get hot enough to (basically) weld themselves together. So you must treat the joining surfaces with a compound during assembly to prevent this fusing of the metals. Here's the stuff Chris Harris recommends.... Right Here

• If the area of seizure is localized to a smallish area, then the threads can be cleaned up well enough to get back in business by using a mechanic's Metric Thread File. This is a special file with rows of triangular teeth with the size and pitch of the damaged thread. You simply match the thread pitch, and carefully file away the offending built-up metal. The resulting thread may not be pristine, but it will be strong enough to hold a new exhaust nut for the remainder of the life of the motorcycle. And although you may be disassembling your machine for the cam shaft, typically a thread file will allow this job to be done with zero disassembly.

Hope this helps.

I've had similar problems over the years, and finally found an inexpensive Chinese die. It's a Links part number GB/T 970.1-94 9SiCr size M52x2. It's not perfect, but is adequate. Once the threads have been cleaned up, use a lot of anti sieze. If you can't find one, let me know and we can work out a loan of mine.
Pete Peterson
Lillian, AL

Found a die on Ebay for $20 from China. If yer gentle, could work
M52x2.

Thanks! The thread file looks very useful in general, I'll snatch one up, though I'm fairly sure the threads in this particular case are too mangled to be fixed with it.

I am aware that the anti-seize (or lack thereof) is the culprit. I didn't put these nuts on years back, a mechanic did (we don't speak of this mechanic anymore), so the lack of anti-seize wasn't a surprise. It's one of the main reasons I never tried to force anything from the start.

Any advice on keeping a die that large centered properly and held securely? I don't have any machining tools, which is the reason my initial reaction is to send the parts out for fixing.
I ordered the die just because, for $20, I'd rather have one on hand for worst-case scenarios, but I'm still hesitant to jump into re-cutting these threads on my own.

Except when I went to pull the exhaust nuts neither of them wanted to budge. After using heat and following plenty of advice on not forcing anything too hard, they still didn't budge. So I very carefully cut them both off and found that the middle section of threads on both sides is completely mangled. The front two or three threads on each side are in good shape.

I see no issue. You stated the first several threads were in good shape. Dies come with gradual lead-in threads to help starting. So between the good threads on the cyl head and lead-in threads on the die, I simply don't see a problem. Simply cover the aluminum threads with some type of lubricant, grease or oil. Cut for a 1/2 turn and remove the die. Thoroughly clean the die of chips, re-lubricate, and start again.

Hope this helps.