Exhaust Rose replacements

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I have the need to replace the exhaust thread roses on a 72 Commando due to previous owner(s) unknown)breaking off some of the fins.

There appears to be various options
Brass dull plated
Brass no plating
Stainless steel
(Maybe other options as well)

can the more experienced people suggest the best option and why?
 
I prefer polished Brass but as long as they are Brass they will work fine. The Brass ones expand with heat at a closer rate to aluminium than steel does, so less likely to loosen over time.
 
I use the RGM stainless nut Jim shows in that video, I like ‘em cos RGM sell a very sturdy purpose designed wrench for them and the ‘fins’ are very thick and strong, so it’s easy to get ‘em in good n tight.

The fact they expand the same as alloy wasn’t known to me until, I saw Jim’s test.

I would highly recommend them.
 
The difference between the five nuts measured by Jim was .004 over a 2 inch diameter. Which for this application is very unlikely to make any practical difference at all.
 
Stephen Hill said:
The difference between the five nuts measured by Jim was .004 over a 2 inch diameter. Which for this application is very unlikely to make any practical difference at all.
Click to expand...

The thing that makes the difference here is the cyclic nature of the exhaust heating and the fact that there is very little 'stretch' involved in the threaded joint. 0.004" could be the difference in loosing all of the preload on the threaded joint and the nut working loose, especially when this factor is applied repeatedly.

I know it does seem trivial, but these things can make all the difference.
 
Derek Wilson said:
The thing that makes the difference here is the cyclic nature of the exhaust heating and the fact that there is very little 'stretch' involved in the threaded joint. 0.004" could be the difference in loosing all of the preload on the threaded joint and the nut working loose, especially when this factor is applied repeatedly.

I know it does seem trivial, but these things can make all the difference.
Click to expand...
I think Jim's study was useful, but I wish the had measured the different in length. Probably could be calculated since the percentage change is probably the same in both directions but the threads getting wider apart might do more to loosen than the diameter - I am certainly no expert - he's the machinist! Also, as I understand his video, he was showing the brass was no better than the rest.

To me it's a moot point. Use some Permatex nickel anti-seize on the threads and you'll get them about a half turn tighter than dry. I've never had one come loose after tightening hot when I installed with the anti-seize. I don't know about copper or aluminum anti-seize - I use nickel as it has a high enough heat rating (2400F) to be effective when hot or cold.
 
marshg246 said:
I think Jim's study was useful, but I wish the had measured the different in length. Probably could be calculated since the percentage change is probably the same in both directions but the threads getting wider apart might do more to loosen than the diameter - I am certainly no expert - he's the machinist! Also, as I understand his video, he was showing the brass was no better than the rest.

To me it's a moot point. Use some Permatex nickel anti-seize on the threads and you'll get them about a half turn tighter than dry. I've never had one come loose after tightening hot when I installed with the anti-seize. I don't know about copper or aluminum anti-seize - I use nickel as it has a high enough heat rating (2400F) to be effective when hot or cold.
Click to expand...

I agree, a little more explanation in the video would have been beneficial to drawing the correct conclusions. I am a mechanical engineer by trade, and I get what Jim was trying to illustrate.

The aluminum nut would be considered the control sample: The head would expand and contract at roughly the same rate of thermal expansion as the aluminum nut - therefore, you would be looking for a nut material that expands at roughly an equivalent rate. As can be seen, the stainless steel expands at the same rate, with the brass nut lagging it by 0.001". The steel nut expands much less, making it the most 'unstable' for holding a heat resistant fit.

You are correct about all other dimensions being proportional, hence he only measured the one. In an ideal design of experiments, you would increase the sample size to be greater than one, as you would have better correlation with a larger statistical sample.
 
I bought a pair of these.


Stainless steel and beautifully made, comes with a great spanner (that is physically very light and strong, Dural?). Not cheap, but cheaper than CNW at least if you are UK based.
The exhaust roses were a tight fit in my FullAuto head, so that is probably because the head was new, and/or because they are made accurately to the correct size. I'm very pleased with them.
I've done 3,000 miles since fitting and they have not come loose.
 
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My key takeaway from Jim’s video is that the material used doesn’t really matter.

The difference between factory standard steel and the brass (or chromed brass) which many manufacturers say is far superior as it mimics the expansion rate of the aluminium head is actually neglible.

Plus if that was a line of thought to pursue, surely you’d want them made from a material that is more stable under heating and cooling than the head.


In my view, there is no substitute for exhaust roses that are well made, with the correct size thread machined onto them.
A lower cost, cast rose where the threads are ‘cleaned up‘ post galvanising or chroming are the ones that will fit poorly, will come undone with the heat cycles and ultimately wallow out the threads in the cylinder head necessitating lock wiring, needing to use retaining clips and ultimately thread repair.
 
Your goal is maximum thread engagement. I use the 828 type rose nuts (with proper tool) , with plenty of threads. Also I smear those threads ( crush rings , collets etc.) with plenty of high temp silicone , re-torque after hot. Never use the retaining rings. BMW airhead make a great tool.
 
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crush rings


The root of the problem.

Should use a non crush-able gasket with a bit of Maniseal [ made and developed in NZ by Cyril Austin { Penitril Laboratories employed a drunkard chemist to work on this stuff } way back, and bought out by CRC ] on both sides. Do the nut up and forget about it.


Crush rings a re supposed to crush, but when do they stop.
 
kerinorton said:
crush rings


The root of the problem.

Should use a non crush-able gasket with a bit of Maniseal [ made and developed in NZ by Cyril Austin { Penitril Laboratories employed a drunkard chemist to work on this stuff } way back, and bought out by CRC ] on both sides. Do the nut up and forget about it.


Crush rings a re supposed to crush, but when do they stop.
Click to expand...
And what may I ask is this non crushable gasket ? Thanks.
 
Reggie said:
I bought a pair of these.


Stainless steel and beautifully made, comes with a great spanner (that is physically very light and strong, Dural?). Not cheap, but cheaper than CNW at least if you are UK based.
The exhaust roses were a tight fit in my FullAuto head, so that is probably because the head was new, and/or because they are made accurately to the correct size. I'm very pleased with them.
I've done 3,000 miles since fitting and they have not come loose.
Click to expand...

I have had these on my race bike since 2014! As you can imagine the engine has been in and out a few times since then!

But wire locking is racer ethos, so always used as part of the mix....which means also that mine are not perhaps quite as pretty as new ones!

I also have a Fullauto head.

You can go direct to Seeger Engineering for them, and they also do exhaust thread insert fitting.
 
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I certainly appreciate JC doing the thermal expansion exercise to debunk the excessive expansion as a major factor of nut fit.
Knowing what the head does thermally would help further show the relationship between them.:)
The test I had done quite a while ago consisted on the actual measurement of pitch diameter using the engineering 3 wire method .
That was certainly eye opening with numbers all over the map.
For info there are 3 norton exhaust nuts.
The basic 3/4" deep small fin 1949-1972 Though they were carried under evolving part #
One year 1973-750 Big fin 3/4" deep threads
850 1/2"effective threads Big fin
ALL NHT ports were 3/4' deep
 
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