Exhaust nuts and expansion

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I'm not good at math but it seems to be the stock one wins.

Yet another great job by Jim!
 
swooshdave said:
I'm not good at math but it seems to be the stock one wins.

Yet another great job by Jim!
Click to expand...

No, the winner is the nut that is closest to the expansion of the aluminum so the cylinder head does not expand away from the nut when it's hot. The RGM cast SS nut is the winner.
 
I'm pretty sure I said I wasn't good at math, right? Did I miss the part where you measured the exhaust port expansion?
 
So why isn't the alu nut the winner if criteria is same expansion as head?
 
comnoz said:
No, but I did measure a cast aluminum nut -similar to the head.
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But the mass of the head is going to expand differently than a smaller nut?

Shouldn't be terribly hard to measure the exhaust port, you only have to do it once. :cool:
 
Tornado said:
So why isn't the alu nut the winner if criteria is same expansion as head?
Click to expand...

It could be except that like metals tend to scuff when in contact so the threads do not wear as well when tightened into an aluminum head.
The fins are also easy to break when tightening.
But I have used them in racebikes for the weight advantage where longevity was not a concern.
And they work very well in my hard bronze exhaust thread inserts but they aren't as good looking as the stainless RGMs
 
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swooshdave said:
But the mass of the head is going to expand differently than a smaller nut?

Shouldn't be terribly hard to measure the exhaust port, you only have to do it once. :cool:
Click to expand...

The expansion of the head should be similar to the nut. The expansion will be determined by the circumference of the hole in the head -just like the nut.

A head won't fit in my small oven.

And the larger oven that I use for heads only goes to 400 degrees.

And I am not going to fire up my big oven just to test one head. Maybe I will test the idea when I have a batch of barrels to stress relieve.
 
As I put in another post recently, IMHO, one of the nice benefits to the RGM nuts is that RGM sell a seriously solid wrench that’s made specifically for these nuts, and this allows you to put some serious torque into them. Being of a solid construction themselves, the nuts take this easily.
 
comnoz
I,m with swooshdave on this one, your cold measurements of the AN and RGM parts are almost identical to mine but the RGM didn,t fit my RH4 or Fullauto heads.
There are signs in your video of potential trouble in the tightness of the RGM part, it shouldn,t need oil to screw freely into the Fullauto, which the AN one does easily dry and when tightened correctly into good threads doesn,t loosen off in my experience. (on Commandos or Atlas)

Your own data on the recent dash6 post in fact shows that steel expansion is actually closer to aluminium than the stainless alloy used for exhaust nuts, which is much higher, and on the RGM nut has a bigger initial dimension (+0.013") and a hot expansion nearly twice that of the steel nut in your test, not a good recipe for piece of mind in service.

This would explain why the OE steel nuts work well when everything is in good order.
On older heads things have deteriorated, but nothing properly machined inserts won,t fix and at the end of the day, while bench testing is important, it,s what happens during longterm everyday riding that counts in this case.
 
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:p
comnoz said:
The expansion of the head should be similar to the nut. The expansion will be determined by the circumference of the hole in the head -just like the nut.

A head won't fit in my small oven.

And the larger oven that I use for heads only goes to 400 degrees.

And I am not going to fire up my big oven just to test one head. Maybe I will test the idea when I have a batch of barrels to stress relieve.
Click to expand...

That’s why God invented Webers. :p
 
KiwiNeill said:
comnoz
the measurements of the AN and RGM parts are almost identical to mine but the RGM didn,t fit either RH4 or Fullauto head.
There are signs in your video of potential trouble in the tightness of the RGM part, it shouldn,t need oil to screw freely into the Fullauto, which the AN one does easily and when tightened correctly into good threads doesn,t loosen off in my experience. (on Commandos or Atlas)

Your own data on the recent dash6 post in fact shows that steel is actually closer to aluminium than the stainless alloy used for exhaust nuts, which is much higher, together with a higher hot expansion nearly twice that of the steel nut in your test.

This would explain why the OE steel nuts work well when everything is in good order, on older heads things have deteriorated, but nothing properly machined inserts won,t fix and at the end of the day, while bench testing is important, it,s what happens during longterm everyday riding that counts in this case.
Click to expand...

I have not experienced any problem using the snug fitting nut. Just the opposite in fact. The snug fitting nut does not tend to come loose.
And I sure have not seen a head that the RGM stainless nut would not screw into by hand with a little oil.
 
KiwiNeill said:
comnoz
I,m with swooshdave on this one, your cold measurements of the AN and RGM parts are almost identical to mine but the RGM didn,t fit my RH4 or Fullauto heads.
There are signs in your video of potential trouble in the tightness of the RGM part, it shouldn,t need oil to screw freely into the Fullauto, which the AN one does easily dry and when tightened correctly into good threads doesn,t loosen off in my experience. (on Commandos or Atlas)

Your own data on the recent dash6 post in fact shows that steel is actually closer to aluminium than the stainless alloy used for exhaust nuts, which is much higher, together with a hot expansion nearly twice that of the steel nut in your test.

This would explain why the OE steel nuts work well when everything is in good order.
On older heads things have deteriorated, but nothing properly machined inserts won,t fix and at the end of the day, while bench testing is important, it,s what happens during longterm everyday riding that counts in this case.
Click to expand...

Neil, I wonder if you simply had faulty nuts supplied?

Concerned by your post, I have just been and tried one of my RGM nuts (which is attached to one of Brooking850s pipes, so not as easy to try as a loose nut) into a head that’s just had a brand new Maney thread insert, and it screwed in finger tight with ease...
 
I guess I did not include the expansion rate of cast aluminum

I narrowed down the alloys a bit and have new numbers but in degrees f instead of kelvin.


Product Linear Temperature Expansion Coefficient ppm/Degrees f

Cast 356a alloy [like a head] - 12
Steel Stainless Austenitic (304) - 9.6
Cast brass - 10
Aluminum Alloy - 6061 13.0
Steel - 7.2

https://psec.uchicago.edu/thermal_coefficients/cte_metals_05517-90143.pdf
 
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comnoz and Fast Eddie
Well rest assured my set didn,t fit actual threads (rather than inserts) while the steel ones did and my findings weren,t challenged by Roger Myer, with a refund (sort of) given when they got the bits back amid mention they would be examined.
Definitely had faulty nuts supplied, not a problem normally but the stuffy response and lack of communication re the original postage legally due, but not given, was a good sign to walk away from this company.
 
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Used the original steel nuts, but did have them powder coated.
I have used ARP fastener lube on a lot of engines over the years, from a Big Healey to a 427 Side Oiler. It has a high temp/low temp. rating of something like -50 to +2000 degrees with a melting point of 400 degrees. I have never experienced any breakdown whatsoever. The copper crush washers are aircraft "wave" style, compressing while still retaining tension, the cost was around $1.00 each. I marked the nuts prior to first start with one minor snug applied to a hot engine, there has been zero drift.

Aircraft wave crush washer

Aircraft wave crush washer

Exhaust nut lube

Exhaust nut lube

 
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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 .
 
I had a pair of aftermarket exhaust nuts that fit into a stock head but wouldn't fit into a FA head.

I have pressed machined plugs through mine to expand them a few thou so they fit tighter. I did this for a head where a nut came loose and wore on the threads a bit (but didn't destroy them). Swelling the exhaust nuts avoided having to install new female threads in the head.
 
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