silencer fractures..

Whilst admiring the suble curves of the Commando this weekend I noticed my left hand silencer was flapping about slightly more than the right hand one. A closer inspection revealed the silencer had fractured just behind the downpipe to silencer clamp, where the pipe flares out. This fracure is all the way round, separating the silencer from the downpipe!
Have I ommitted to follow a build procedure which would have avoided this problem, or do all Commandos shed their silencers in such a fashion?
Regards, Stuart.

you are not alone on this. I have had one of my viking silencers do this a couple of years ago. the good news was I purchased them from old britts and he was kind enough to warranty it.

Two pair of my Vikings did the same about 3000 miles into their life. These breaks and the head flanges letting go added many TIG welding charges to the 2600 price tag. Be careful what you wish for.

The only pipes I've seen and heard of that fracture there are Viking brand.

Did a roadside fix with some tape on the right side Viking pipe on this one a couple years back-

Barring bad design defects,I reckon header pipe alignment has an effect on the mufflers as well as the ex port nuts,now that my pipes run blue to just above the second bend they are self aligning after a good hard ride :roll: :roll: now I will just wait for them to rust off.

Very tasteful bike GP

Jean

The bike belongs (belonged?) to a friend who moved out to Cali. As you can see from the photo info, it came off the website of "Big D" cycles, they built it for him.

He had the pipe welded up, don't know if he ever re-chromed it. From what I've heard, once a muffler cracks like that, they will continue to crack in other places if welded.

He had over $20K into it, and was wanting to sell it for $10K, about 3 years ago. I lost touch with him though...

This tightening sequence service bulletin might help. Keep in mind it was for the 850's with crossover pipe, but I suppose it may be applicable and help prevent fractures. I'd ignore the part about the lockring tab washers as these are generally not used.

SERVICE RELEASE

CATEGORY OF RELEASE: NATURE OF RELEASE:

Recommended assembly sequence - exhaust system

MODELS AFFECTED: 1973 850c.c. Commando

DISTRIBUTION: Worldwide (General Distribution)

EXPLANATION: Below is an extract of publication NV1300 "Fitting Exhaust System - Assembly Sequence" which is now included with the instructional literature in each new motorcycle case.

In order to eliminate possible stresses introduced into the exhaust system during assembly and fitting, follow the procedure outlined below:-

ACTION:

1. Fit L.H. exhaust pipe complete with lockring, sealing and tab washers. Run up lockring but do not tighten at this stage.

2. Fit L.H. muffler to exhaust pipe, align the mounting pommels and assemble loosely to the L.H. muffler bracket mounting rubbers.

3. Fit R.R. exhaust pipe complete with lockring sealing and tab washers. Run up lockring but do not tighten.

4. Fit R.H. muffler to exhaust pipe, align the mounting pommels and assemble loosely to the R.H. muffler bracket mounting rubbers.

5. Slide both connector sleeves to the centre of the cross tube. Place cross tube in position and slide both connector sleeves outwards to engage with the C~~5t pipe stubs.

6. Slacken off all footpeg support and muffler bracket bolts in the left and right hand aluminium support plate castings - to allow the bracket6 to swivel and adjust to the exhaust pipe/muffler alignment.

7. Tighten up the total exhaust system, commencing at the cylinder head lockrings and cross tube connector sleeves. Do not forget to bend up the lockring tab washers.

8. Finally retighten the muffler bracket/support plate bolts.

NORTON VILLERS CANADA LIMITED
May 1973

I rather like the Commando exhaust set up. As a road tester once pointed out, when the bike is sitting at a traffic lights the silencers flail around impressing small boys and scaring old ladies in bus queues.

The only thing that gives me more pleasure is watching the front wheel and mudguard jumping up and down at tickover. :shock:

I've had one rather old and battered silencer crack at the front weld over the years.

I agree with Ludwig, there's just too much engine movement relative to the exhaust system, which is anchored to the frame. My '69 S-type fractured the silencers at the mounting bosses. This was a chronic problem, which was one of the factors that lead me to sell the bike.

And this movement problem is why the exhaust threads in Norton heads become damaged. You gota really heave-ho on that exhaust nut to keep it from backing and damaging the threads.

I used to find with Taiwanese cheapies one would fall apart each year - even left most of one on the road somewhere without noticing until i got home once.
Have had a good run with Vikings.

exaust pipes

Thanks Trinorman.
I have purchased some RGM replacements, which are probably cheap copies.
I will use your sequence to see if it helps.
At the end of the day we have two stresses going on:-
1) Any static stresses which are due to incorrect alignment whilst fitting.
2) Stresses due to engine movement.

We cannot do anything about the latter but we can eliminate the fitting alignment stresses.

I had the same break on a EMGO... won't buy those again.



More in the old thread here.
http://accessnorton.com/norton_commando2051.html?highlight=&sid=c8960d7016b358fc06161ef2e0ce7156