Exhaust nuts and expansion

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oldmikew said:
Back in the day, I tried Aluminium thinking there might be some thermal advantage. One went on fine, the other somehow either seized or x threaded . With great trepidation started engine and once the head was warm it was possible to get it out. Since then have stuck with the original nuts .
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Alloy to alloy can lock up solid. I once screwed an alloy oil seal holder into a fork leg, it went a bit tight, but when I tried to undo it, it was solid, I had to get it machined out. It would be rather inconvenient if this happened to a head in situ !
 
Fast Eddie said:
Alloy to alloy can lock up solid. I once screwed an alloy oil seal holder into a fork leg, it went a bit tight, but when I tried to undo it, it was solid, I had to get it machined out. It would be rather inconvenient if this happened to a head in situ !
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It was a very stressful experience!!! But I wonder how many of these stripped exhaust threads are actually caused by over tightening?
 
oldmikew said:
It was a very stressful experience!!! But I wonder how many of these stripped exhaust threads are actually caused by over tightening?
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A lot.
I always try to have conversation with myself about not over tightening.
Learned that the hard way.
 
I'm confused about something. Which shouldn't be a big revelation. But the RGM nuts are bigger than the others cold. The bronze nut is smaller and only expands to the average size after heating. Wouldn't this be a huge factor? The RGM nut ends up being 20 thou bigger than the bronze nut.
 
comnoz said:
My take-
If the threads are weak enough that you can strip them by tightening, then they would have gone soon anyway.
With good thread depth of engagement you can lean on them hard enough to strip the fins before you strip the threads.
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That makes sense- I use a 3ft length of pipe over a C spanner that fits the fins. So a serious amount of torque. If so tightened with a warm engine and the tabs on the locking washers are located then the pipe does not work loose. And presumably it is loose pipes that wear the thread . And I am still using my original head and threads are good. What puzzles me is how the tab washer lets the nut back off sufficiently for a loose pipe .
 
+1

comnoz said:
My take-
If the threads are weak enough that you can strip them by tightening, then they would have gone soon anyway.
With good thread depth of engagement you can lean on them hard enough to strip the fins before you strip the threads.
Click to expand...
 
rvich said:
I'm confused about something. Which shouldn't be a big revelation. But the RGM nuts are bigger than the others cold. The bronze nut is smaller and only expands to the average size after heating. Wouldn't this be a huge factor? The RGM nut ends up being 20 thou bigger than the bronze nut.
Click to expand...

Yes, In this case the RGM nut is .020 larger than the bronze nut.
That is not always the case.
I have run into some bronze nuts that were larger than the RGM nuts.

My experience so far with the size of the stainless RGM nuts and the stainless CNW nut has been good. I make a lot of inserts for those two nuts with only two variations in my programming.

When it comes to inserts for the stock nuts they vary a lot and I need the nut if I am going to make a good fit.

I don't recommend bronze nuts with my aluminum bronze inserts because of the problems created by similar metals in contact.
 
Various alloys/metals offer a tremendous amount of elasticity, but this “flex” is only realized at extremely high tolerances. Different alloys hit their flex range at different pressures/temperatures. The stronger of the two eventually compromises the weaker, especially when constantly cycled through hi -low temperature ranges, thus a second torquing on a hot engine.

The older “seasoned” metal of an original thread on the exhaust port of a 50 year old cylinder head matched up to a new set of male threads of a modern day alloy fastener is going to require proper prep and a sensible application of finesse/tightening/torque.

I would argue that extending the leverage of your fastening tool by 3 feet and then cranking down on it will definitely go wrong sooner rather than later.
If you have to apply that much pressure it seems to me one would be trying to compensate for an already existing problem.

Then again I have seen farming equipment slapped together with “bailing wire” that I figured would let go within the hour last years.
 
Lineslinger said:
Various alloys/metals offer a tremendous amount of elasticity, but this “flex” is only realized at extremely high tolerances. Different alloys hit their flex range at different pressures/temperatures. The stronger of the two eventually compromises the weaker, especially when constantly cycled through hi -low temperature ranges, thus a second torquing on a hot engine.

The older “seasoned” metal of an original thread on the exhaust port of a 50 year old cylinder head matched up to a new set of male threads of a modern day alloy fastener is going to require proper prep and a sensible application of finesse/tightening/torque.

I would argue that extending the leverage of your fastening tool by 3 feet and then cranking down on it will definitely go wrong sooner rather than later.
If you have to apply that much pressure it seems to me one would be trying to compensate for an already existing problem.

Then again I have seen farming equipment slapped together with “bailing wire” that I figured would let go within the hour last years.
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Well yes but its not something I intend to do...once bit 50 years ago twice shy.. As for my three feet extension , well using that is a matter of feel..but its only really necessary for the final tweak.
 
[QUOTE="oldmikew, post: 403320, member: 7883. "but its only really necessary for the final tweak. .[/QUOTE]

AKA finesse.:)
 
bill said:
+1
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+2
Many years ago I did a full set of 3 wire measurements on a whole bunch of exhaust roses. from 1950 M7 through 1975. As I expected there was quite a spread of thread diameters.
Measuring the "peak OD" of the thread does not indicate the diameter of the thread. I also had one set of aluminum nuts, which I would only use as for a static display or for"show" and still antiseize them.
I would probably not use SS exhaust nuts.
 
Overtightening and lock tabs are worthless because after vibration and heat cycles the nuts are still going to loosen up even if they don't turn. You have to keep checking them and retightening them as time goes by. If you forget for too long they are going to loosen and blow out the threads. There are exceptions and they may stay tight after enough re-torques with the right material. But so many damaged heads point to this being a continuous problem and design flaw. Its even worse in racing because of the vibration caused by the severe wide open exhaust note blast and the only way I could keep things together was to make the modification below (with a spacer and a smear of silicone). And I still had to retighten them a couple times till they fully bottomed out and settled. The spring allows the pipe to move inside the nut instead of pounding out the threads.

Exhaust nuts and expansion
 
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jseng1 said:
Overtightening and lock tabs are worthless because after vibration and heat cycles the nuts are still going to loosen up even if they don't turn. You have to keep checking them and retightening them as time goes by. If you forget for too long they are going to loosen and blow out the threads. There are exceptions and they may stay tight after enough re-torques with the right material. But so many damaged heads point to this being a continuous problem and design flaw. Its even worse in racing because of the vibration caused by the severe wide open exhaust note blast and the only way I could keep things together was to make the modification below (with a spacer and a smear of silicone). And I still had to retighten them a couple times till they fully bottomed out and settled. The spring allows the pipe to move inside the nut instead of pounding out the threads.

Exhaust nuts and expansion
Click to expand...

I use much the same thing - just a short piece of threaded pipe which is screwed gently home against a heat resistant washer from a Japanese bike - slip joints and springs on the pipes and NO INTERNAL STEPS. If you hang exhaust pipes using the original finned nuts, you will always have problems. I use a 2 into 1 exhaust, so the pipe does not rock around with the vibration of the motor, as much as with separate pipes. I hold the other ends of the springs with tags off two rocker box screws. The way Jim has the springs in this photo, you still work the threads in the head.
 
I had Jim add his beautiful aluminum-bronze inserts to my '74 after someone had already done a botched insert job years ago, installed the stock iron nuts using anti-seize compound, leaned on them hard with a 24" tool when cold, repeated once hot, then at the next couple of fuel fill-ups. After a couple of those, the wrench no longer moved (no, they weren't seized...), and they've remained like that for close to 10,000 miles. No springs; no lock tabs; 25 miles a day on the freeway. I checked them a couple times after, but nothing since the initial bedding-in. I'm happy, to say the least!

Nathan
 
Nater-Potater
That is the technique I always used with the original 850 steel nuts in my (non insert) RH4 and Fullauto heads with the same result and no damage to the threads on either. Loctite dark grey antiseize used but most brands OK.
The Fullauto has now done over 6000 miles since last July and both nuts still reassuringly tight since initial bedding in as you describe.
Still ridden daily at the mo and I,m fettling a spare pair of 850 steel nuts for rechroming and fitting in the summer, for cosmetic posing reasons only as they look great...
Removing and tightening always done on a hot motor apart from initial cold fit install.

My non balanced Mk3 twin pipes use a combination of the Mk3 spherical collars sitting on standard FJ1200 /FZR1000 exhaust gasket rings, the usual Japanese type, ceramic material within ribbed stainless inner and outer walls, tough, leakproof and compact this allows the nuts to use most of the available threads on my setup.
 
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