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Topic-icon R75 Buggered Exhaust Threads

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3 weeks 1 day ago - 3 weeks 1 day ago #5781 by cyclingsocialist
R75 Buggered Exhaust Threads was created by cyclingsocialist
The quick and dirty:
My R75/6 needs a camshaft replacement. No sweat! 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.

Where I need help:
I'm in Houston, Texas and I don't know any other airheads. I do 99% of my own wrenching but don't have the capabilities to rethread these exhaust ports. If anyone is familiar with a machinist here who can reliably do work like this, please let me know! Even better if someone already has a line on a die that works for this, because I have a feeling if I find my own machinist they're going to have to fabricate the die.

The front two or three threads on each side are in good shape. I haven't run the new fin nuts over them (I'm full of bad ideas, but that wasn't one of them), and obviously they should be retraced just to be sure, but it's my understanding that it only takes three threads to hold the nuts securely. So going with that, I think just cutting the threads again will be sufficient, I won't need to have new material added.

Any advice, I'm all ears!

Thanks.
Last edit: 3 weeks 1 day ago by cyclingsocialist.
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3 weeks 1 day ago - 3 weeks 1 day ago #5782 by 8166
Replied by 8166 on topic R75 Buggered Exhaust Threads
You did well to cut the exhaust nuts off instead of doing further damage to the threads on the spigots. You can find vendors on Amazon that'll sell you a die, but make sure it's not so big that it won't thread all the way down to the head. The one I purchased would not.

At the end of the day, the best approach is to send the heads off to a specialist that is both equipped and is familiar with this work. I recommend Randy Long, who charged $75/head last time I had this problem. Here's his contact info:

Long's Mechanical Services
‭(610) 286-5870‬
74 Risbon Rd.
Honey Brook PA 19344

Randy's not a computer guy, so the best way to arrange services is to call him.

Before you send the heads off, remove all the valve gear. If you don't, Randy will have to do it and he'll charge you for doing so.

Randy will likely ask you to include a new exhaust nut in the package so he'll have something to check the new threads against.

When you pack the heads, wrap each one in sheet foam (NOT bubble wrap), put each one in a box, wrap those boxes in more foam, and put the two of 'em in another box. Make sure that nothing's loose when you shake any of the boxes. And when you ship, insure it for $600/head, as that's what it'll cost to replace them if they become lost or damaged. When tracking on the box shows it has arrived, call Randy again to let him know. Sometimes he forgets to open boxes...

8166 Scot Marburger, This email address is being protected from spambots. You need JavaScript enabled to view it.
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Last edit: 3 weeks 1 day ago by 8166.
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3 weeks 1 day ago - 3 weeks 18 hours ago #5783 by Wobbly
Replied by Wobbly on topic R75 Buggered Exhaust Threads
• 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.

Don't hide 'em, Ride 'em !!
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Last edit: 3 weeks 18 hours ago by Wobbly.

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3 weeks 1 day ago #5784 by 10665
Replied by 10665 on topic R75 Buggered Exhaust Threads
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
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3 weeks 1 day ago #5785 by 15295
Replied by 15295 on topic R75 Buggered Exhaust Threads
Found a die on Ebay for $20 from China. If yer gentle, could work
M52x2.
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3 weeks 11 hours ago #5786 by cyclingsocialist
Replied by cyclingsocialist on topic R75 Buggered Exhaust Threads
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.

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