Broken exhaust nut

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PJL

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I've not long bought a 1972 Commando Interstate and am in the process of servicing it ready to put it on the road for the first time in 5 years.

Today I was trying to remove the right hand exhaust, and the exhaust nut (or ring, or rose) snapped off 3/4 of the fins (I was using the correct tool!). Is there a straightforward way to extract the remains of the exhaust nut from the head?

I'm not keen to dismantle it. I've not even ridden it on the road yet! I've got this nagging feeling that the head will have to come off and go to a specialist for repair. Oh, by the way, can one get the head off with the engine in the frame?

I must admit to being surprised by the poor quality and lack of thickness of the aluminium alloy used for the exhaust nut. The system on my MZ 250, also a screwed nut round the pipe, is far better, made of steel. It also has to cope with an engine bouncing up and down, just like the Commando. It rarely comes loose as long as one uses a bit of silicone sealant and tightens using a 2 foot bar.

Best regards, Phil.
 

L.A.B.

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PJL said:
Is there a straightforward way to extract the remains of the exhaust nut from the head?

I suggest that you run the engine (if possible) until the cylinder head is HOT then pour cold water over the nut to contract the nut away from the head and try again? Although you may end up having to use a hammer and chisel on the nut?

PJL said:
Oh, by the way, can one get the head off with the engine in the frame?

Yes, although the pushrods do need to be held up inside the head and lifted off with the head.

(I would recommend that owners have a copy of the relevant workshop manual handy? Answers to basic questions will then be at their fingertips.)
Here's a free one: http://rocbo.lautre.net/technique/norto ... p/004.html


PJL said:
I must admit to being surprised by the poor quality and lack of thickness of the aluminium alloy used for the exhaust nut.

If they are aluminium then they are probably not the original Norton parts?
 
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I'm sure all correct exhaust nuts should have four thicker fins, these are the ones to lever or hammer on. Follow LAB's advice though shock rather than pure torque can have a better effect.
Best of luck,
Cash
 

PJL

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Thanks for the advice. I was coming to the same conclusion upon thinking about it more this morning -> run the engine, get it really hot, then have a go on the remaining three fins (unfortunately none being the thick variety). At least for the moment it's still tight.

You never know, if I run the bike for a bit, it might come loose by itself, judging by the correspondance on this subject in the forum.

I looked up the available lock rings on the Norvil site, they list three types, aluminium, chromed and alloy. What's the collective experience of which is the best type?

The spare I got with the bike is alloy.

Best regards, Phil.
 

L.A.B.

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PJL said:
I looked up the available lock rings on the Norvil site, they list three types, aluminium, chromed and alloy. What's the collective experience of which is the best type?

As I understand it, the best ones to use are the bronze type: http://www.norvilmotorcycle.co.uk/010399.htm "LOCKRING - EXHAUST - BRONZE - FOR UNBALANCED PIPES - STAY TIGHT" as they are supposed to expand at roughly the same rate as the cylinder head, same as the alloy (aluminium) ones should, unlike the plated steel type which do not, so tend to loosen as the engine gets hot, and is the reason why the steel ones need to be tightened with the engine quite hot.
As you have already discovered the alloy ones could be difficult to loosen without damaging them, but maybe they don't need to be tightened up as much as the steel ones do?

Neither of the part numbers listed by Norvil for the aluminium or bronze nuts can be found on the ANIL website, so those parts are likely to be Norvil's own, not that there's likely to be anything wrong with that.
I do seem to remember reading somewhere that the Norton factory could have briefly experimented by fitting the alloy or bronze nuts, but I can't remember where I read that, or any of the details. The only ones listed by ANIL are the steel types.
 
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The Bronze ones I use I am sure are off a pre-commando Norton Twin, I found them in a box in an autojumble and have small fins, they never come loose except for when I ask them too :lol: .
 
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If you don't need to remove the exhaust right away it's not a bad idea to just run as is and wait for it to loosen on its own!

The nuts that came with my 750 are some sort of pot metal or maybe alloy, I don't know. I've never had a problem with them loosening, whatever they are. On my old 850, however, I could not keep the nuts tight no matter what I did. That was with the stock crossover exhaust and OEM nuts. Back then I didn't know about tightening while hot though. I used to use the tab washers and all that got me was stripped threads.

I recently bought a new set of nuts for my 850 project from Andover. They are brass or bronze (I don't know how to tell the difference) that has been (rather poorly) chrome plated.

Debby
72 750
74 850 project bike
 

PJL

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Just to finish this thread, I now have removed the broken exhaust nut. I've taken the engine out to deal with the 72 breather anyway.

There was nothing of the exhaust nut left to grip, so I carefully drilled into the remains of the nut with a 2 mm drill, parallel to the pipe, several times, to create a notch. Then, clamp head to workbench (Black & Decker workmate, with convenient holes in it), place blade of screwdriver into notch, clamp to exhaust pipe and rotate exhaust. The nut started rotating. Great! Then just worked exhaust back and forth re-clamping the screwdriver blade each time.

I will rebuild with the bronze exhaust nuts, which look to be stronger than the aluminium alloy version.

Best regards, Phil.
 
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