Engineering compromises leading to exhaust threads stripped (2012)

[Klaus Monning]

Best I can see is, the exhaust threads being a problem area, is the result of multiple engineering EVOLUTION compromises. In the beginning, the head was cast iron and the threaded attachments probably worked just fine. Then the thread (head) material changed to softer aluminum... and they probably still worked OK. Then the Commando with Isolastic engine mounting system introduced lots of motion. And the four foot long pipe with a muffler hung on the end was hard to move from one end, overstressing the threaded joint. Then, in '74, the crossover pipe was added, requiring a shorter nut to make room for the split keepers now mandated by the crossover. 25% less threads engaged, failing even faster than ever. Item 17 here: http://www.oldbritts.com/1973_g23.html

As much as I want to keep my bike original, the crossover pipes are being binned. The longer nuts to engage all the threads will be added, along with a better engineered mounting system, to be detailed later.

Hello,
I never had this problem. Indeed the exhaust threads are a critical point.
I only use aluminium nuts with a bit of anti seeze- paste.
The main problem is the aluminium head and steel- nuts. With rising temperature the head expands wider than the nuts. How much ever you tighten your steel- nuts the more you damage the threads.
The aluminium- head and aluminium- nuts expand at the same rate with rising temperature. You don't even have to tighten aluminium nuts all that much. After you re- tighten them after you fitted new seal rings they stay tight.
Best Regards
Klaus

 

[Torontonian]

Hello,
I never had this problem. Indeed the exhaust threads are a critical point.
I only use aluminium nuts with a bit of anti seeze- paste.
The main problem is the aluminium head and steel- nuts. With rising temperature the head expands wider than the nuts. How much ever you tighten your steel- nuts the more you damage the threads.
The aluminium- head and aluminium- nuts expand at the same rate with rising temperature. You don't even have to tighten aluminium nuts all that much. After you re- tighten them after you fitted new seal rings they stay tight.
Best Regards
Klaus

Who sells them please.

 

[concours]

The problem is a FIVE FOOT lever secured at one end.

Grab a Christmas wrapping paper tube by 1/2” on one end only, wiggle it quickly, try to hold on.

While differing expansion rates of steel/alloy IS a problem, it’s overcome by overtightening.

 

[74ok]

Re: Engineering compromises leading to exhaust threads strip

There are other threads (no pun intended) on this subject, Ludwig made the best looking and probably best all around permanent repair to his Norton.

Jean

exhaust-port-repairs-t3373.html?hilit=exhaust

Any more info from above post on page 1? above link doesn't work & couldn't find..

but did run across this
https://www.accessnorton.com/NortonCommando/exhaust-port-repairs.3261/

https://www.accessnorton.com/NortonCommando/exhaust-port-repairs.3261/#post-29331

& this
https://www.accessnorton.com/NortonCommando/exhaust-nuts-and-expansion.26838/#post-403139

 

[Klaus Monning]

Who sells them please.

Hello,
I got mine via eBay.com. They were made in the US. Unfortunately now I can't find them anymore. I try and go through my paypal- files.
Best Regards
Klaus

 

[Matchless]

BMW air heads use aluminium exhaust nuts. Whilst they don't work loose in use they do have a habit os seizing onto the head after extended periods, even when anti seize compound has been applied. This isn't a problem however, as they are on the outside of the head & can be split using a pad saw or similar. This would obviously not be so easy on a Norton.

 

[L.A.B.]

The current AN exhaust lockrings are chrome plated bronze:

https://www.accessnorton.com/NortonCommando/850-exhaust-nuts-prices.7666/#post-97825

 

[dobba99]

My Solution.
I've never been happy with the amount of thread engagement that the ring nut has into the cylinder head. Even when i bought my MK3 i wired both the nuts together before i rode it home from the vendors house (he said you don't have to do that, its never been a problem....)
Once home i cut the wire off and replaced it with two loops of stainless wire and a strong tension spring (robbed off a fold up chair)
Later, when removing the exhaust and fully appreciating the space taken up with the exhaust gasket, spherical seat, flared end of the header pipe and split collet its no wonder these things have a habit of coming loose. The MK3 must be the worst in this respect.
To help matters i turned up much thinner spherical seats and collets and have increased the nuts thread engagement by at least 30%.
You gain 2.5 to 3mm more thread engagement. And use the biggest C spanner you can lay your hands on!


exhaust ring nut, original collet, flared exhaust pipe, spherical seat and gasket


exhaust ring nut, new thin collet, flared exhaust pipe, new thin spherical seat and gasket


new thin and old thick collets and spherical seats


Original rings nipped up in a spare head, large gap, unused thread showing less exhaust ring engagement


Thin rings fitted to Mitzi, Small gap, no threads showing, full exhaust ring engagement



The beauty of doing it this way is that it is fully reversible, No holes drilled in fins etc

 

[L.A.B.]

Later, when removing the exhaust and fully appreciating the space taken up with the exhaust gasket, spherical seat, flared end of the header pipe and split collet its no wonder these things have a habit of coming loose.

Exhaust gaskets aren't used with flared pipes and spherical seatings.
https://andover-norton.co.uk/en/shop-drawing/147/exhausts-mufflers-passenger-footpegs
(Item 31 on the drawing is the collet and 32 is the spherical seating)

 

[L.A.B.]

The MK3 must be the worst in this respect.

Not if there's no additional exhaust gasket.

 

[dobba99]

Exhaust gaskets aren't used with flared pipes and spherical seatings.
https://andover-norton.co.uk/en/shop-drawing/147/exhausts-mufflers-passenger-footpegs
(Item 31 on the drawing is the collet and 32 is the spherical seating)

Surprisingly, i only found that out a few days ago when i was asked by another MK3 owner to have a look at his bike as it had an oil leak from the cylinder head somewhere. I had to remove the balanced exhaust system to be able to view between the fins at the front of the head. Upon exhaust removal i commented that it didn't have any gaskets and Rob replied 'the manual doesn't show any' Really?, i said
All the other Mk3's ive worked on have had the 'extra' gasket fitted, it does make one wonder who has worked on these machines in the past!
Robs bike was an exhaust ring nut failure waiting to happen. The exhaust rings had at max only about four threads engagement, not enough to hold the system securely.
With all the different exhaust pipe makes about and the different variety of exhaust rings available, one can easily get a combination of parts that don't have enough thread engagement
Looking closely at the original exhaust ring and comparing it to the pattern exhaust ring on Robs bike. The Pattern rings thread was well chamfered, where as the original rings thread went right to the edge. Thats one thread gone already.

 

[Danno]

I know a lot of owners have dealt with stripped exhaust threads and that there are folks well-versed in the repair, but I've never had a problem with stripped threads. Probably shouldn't have said so as the next time I remove a Norton exhaust, I'll probably get a handful of stripped head threads, but I think most stripped exhaust threads start with misuse, lack of tightening after 1st warm-up and neglect checking tightness from time to time. My point is, not making something idiot-proof is NOT an engineering compromise.

 

[MexicoMike]

Never had the problem either with the 750-style (unbalanced) pipes or the current balanced pipes on my 850. I use anti-seize on the threads and safety wire on the exhaust nuts.


New Norton Owner: "What parts should I safety wire?"

Old Norton Owner: "Only the parts that you want to keep."

 

[mdt-son]

While differing expansion rates of steel/alloy IS a problem, it’s overcome by overtightening.

I beg to disagree. Overtightening will inevitable damage the threads and the nut will become loose due to vibrations and subsequent re-torquing.
The solutions is either to fit nuts having a CTE close to aluminum, or provide a flange type of bolted joining.
https://www.accessnorton.com/NortonCommando/best-material-for-exhaust-nuts.15118/

-Knut

 

[concours]

I know a lot of owners have dealt with stripped exhaust threads and that there are folks well-versed in the repair, but I've never had a problem with stripped threads. Probably shouldn't have said so as the next time I remove a Norton exhaust, I'll probably get a handful of stripped head threads, but I think most stripped exhaust threads start with misuse, lack of tightening after 1st warm-up and neglect checking tightness from time to time. My point is, not making something idiot-proof is NOT an engineering compromise.

I’ve been called an idiot before.
So, all are idiots who’ve had to deal with those problem?
Of course.
I fix stuff.
Lots of it.
Wildly complex & expensive stuff sometimes.
Do/say what you will.
I offered to share for free an idea.
Seams it’s working well.
Low cost.
Many bikes will never need the solution, because, well, their owners aren’t idiots.
And would NEVER ride them fast or far, never mind BOTH at once.
Like my oil-tight primary fix, clearly, non-idiot owners don’t need it either.
Merry Christmas

 

[concours]

I beg to disagree. Overtightening will inevitable damage the threads and the nut will become loose due to vibrations and subsequent re-torquing.
The solutions is either to fit nuts having a CTE close to aluminum, or provide a flange type of bolted joining.
https://www.accessnorton.com/NortonCommando/best-material-for-exhaust-nuts.15118/

-Knut

Duly noted.
What is the torque specification for the nut?

 

[MexicoMike]

'Like my oil-tight primary fix, clearly, non-idiot owners don’t need it either.''

I had one of those leak-free primary and engine cases for years until suddenly, when we returned to Mexico (where the bike is located) a week ago, there was a puddle of oil under the bike. I guess it had enough of being leak-free for years and returned to its roots.

 

[concours]

Those header clamps won't keep the threads from blowing out if the ex nuts get loose - and the nuts do loosen up from heat and vibration. Eliminate the ex pipe flange and the washers. Run the ex nut in as far and tight as you can (re torque when hot) with silicone on the threads instead of anti seize. Use silicone bronze to Braze a spring hook and a bushing to the pipe and hold the pipe in with a spring to a fin on the ex nut (add a smear of silicon to the bushing so there are no air leaks) - problem solved forever.

That is a good compromise as well.
My aftermarket expansion chambers have a double sleeve type. They are wearing ok, but eventually will need repair. ( I have pictures to share, once I find them)

Here is a great example of a PROPER swivel joint on a rubber mounted power sports engine:

Item 17 & 47. Spherical graphlex reinforced with inconel mesh. $20

 

[dobba99]

Duly noted.
What is the torque specification for the nut?

My spec for torquing the zorst
C spanner and two foot of inch pipe. Bike on center stand and enough umpty to start to lift/tilt the bike (obviously don't tip the bike off its stand !)

 

[Fast Eddie]

RGM exhaust nuts, RGM special C spanner, a fork stanchion slipped over the C spanner handle and tighten to the point of lifting the bike with the engine hot AND still running.

Works for me.