Exhaust mounting modification?

[Andy Higham]

I was thinking about the commando's tendency to work the exhaust roses loose.
The engine end of the pipes is attached to the engine which is wiggling around, the silencers are attached to the frame which isn't wiggling around. In effect the pipes are being flexed back and forth in the head which is putting a lot of strain on the exhaust threads.

My thought is to fit stays from the down pipes to the outer front cylinder base studs, this will stop any flexing at the head / pipe interface.

Any opinions on this?

 

[L.A.B.]

the silencers are attached to the frame which isn't wiggling around.

The silencers are attached by rubber mounts so they move with the pipes.

 

[baz]

I was thinking about the commando's tendency to work the exhaust roses loose.
The engine end of the pipes is attached to the engine which is wiggling around, the silencers are attached to the frame which isn't wiggling around. In effect the pipes are being flexed back and forth in the head which is putting a lot of strain on the exhaust threads.

My thought is to fit stays from the down pipes to the outer front cylinder base studs, this will stop any flexing at the head / pipe interface.

Any opinions on this?

Yes bracing from the engine plates or the engine can help
Also not using silencer clamps can help
There's a lot of posts on here about tightening the exhaust roses but basically tighten with the engine hot and running
And don't use those exhaust tab washers

 

[o0norton0o]

The best adaption I have seen is Ludwig's bike. He mounted a pair of supports for his pipes that pass under the frame and are fastened to the cradle which moves with the engine, so his support for the pipes moves in concert with the engine too.. I'm not sure what he does to support the muffler beyond that point, but perhaps they are supported enough by the cradle support which would completely take all the leverage stress off the joint at the head by allowing the pipe and engine to move together... Maybe he'll chime in here with a good picture.... and I'll be off to copy yet another modification project

 

[Richard Tool]

Simply use bronze exhaust roses . Tighten after several heat / cool cycles … I have not had any loosening in three years.
Be certain that the tooth on the C spanner engages the rose at the root.If it doesn’t you risk breaking the bronze fins. Don’t ask me how I know …

 

[concours]

Thread 'Engineering compromises leading to exhaust threads stripped (2012)'

Sep 13, 2012

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...

• concours
• Replies: 155
• Forum: Norton Commando Forum

• 

 

[B+Bogus]

Simply use bronze exhaust roses . Tighten after several heat / cool cycles … I have not had any loosening in three years.
Be certain that the tooth on the C spanner engages the rose at the root.If it doesn’t you risk breaking the bronze fins. Don’t ask me how I know …

The best ones I found were OEM style (early design) with blocked out fins 120 degrees apart like the photo, but they were bronze.
I can't find a source now, but I think they may have been from Mick Hemmings?

 

[mdt-son]

Seager Enginering supplies exhaust roses made of bronze, and I believe Jim Comstock does (did?) the same.
They have larger fins though.

- Knut

 

[Richard Tool]

Mine came from Norvil IIRC…

https://www.accessnorton.com/attachments/0odxxo-webp.90357/

No need for tab washers .

 

[Matchless]

Seager Enginering supplies exhaust roses made of bronze, and I believe Jim Comstock does (did?) the same.
They have larger fins though.

- Knut

Seager roses are made from a grade of stainless. Maybe 303 but not sure. I have them on three Norton twins & they work well.

 

[Fast Eddie]

Nice summary from Jim Comstock on exhaust nuts…

 

[Rich_j]

There are two categories of Commndo owners, the ones that stick a length of old exhaust pipe over the the lock ring tool, double the length and haul the thing up hard, and all the others whose nuts come loose and waste money on fancy rings or lockwire to the fins and rip out the holes ........
The standard tool is simply too short and owners are too worried about stripping threads. Loose rings destroy threads, you can't overtighten them.
No issues in over 30 years.

 

[ludwig]

or :

 

[baz]

or :

That's a lot more elegant than my solutions over the years
My studs pick up on the cylinder head bolts so there's no alteration to the head itself

 

[Carl H]

A retighten of the rose nuts after a few heat cycles and Aircraft type safety wire (racing) techniques and one drill hole in the a fin properly placed. Some nuts break fins easily as they were made with crappy materials.

Done right it adds a professional touch to your job. I've been doing it for 40 years, No problems. It's simple, cost effective and tech inspectors insist on it.

 

[Mart UK]

I used my Big Bertha firm rubber mallet on the spanner, when the engine was hot. Hated doing it. Amazed I got about 1/4 of a turn further. I was particularly concerned I might harm the balance pipe, but it was fine.

The nut's not moved since.

 

[ludwig]

I said it a few times before, and will say it again: Tighten the rose nut with RUNNING engine!
No need for hammers or brute force. Rev it to 4000 rpm. The vibrations will eliminate all friction.
(that's why they come loose in the 1st place..)
Easy, and much nicer for the threads in the cyl. head.

 

[nortonmargie]

I used my Big Bertha firm rubber mallet on the spanner, when the engine was hot. Hated doing it. Amazed I got about 1/4 of a turn further. I was particularly concerned I might harm the balance pipe, but it was fine.

The nut's not moved since.

I used my heavy copper mallet on the spanner when the engine was hot, figuring I was too small a person to do any damage, got another eighth of a turn and the nut on the engine has not moved since. The nut behind the bars is a different story...

 

[ludwig]

Back on track: I attached the mufflers directly to the engine cradle to stop the header pipes from cracking.
Originally, the bike came with balanced pipes (850 Mk 2A)
After long stretches of 'autoroute' usually coming from southern France, the pipes invariably cracked at the balance pipe weld. Fixing them to the engine cradle stopped that.
First I made rather crude supports, but they worked well, and hardly visible on the bike.
LH is a bit tricky because it has to clear the chain:





Years later I made an alloy engine cradle with provisions for the muffler supports.
A much neater solution, but I doubt the OP will go this far:








Mufflers are also shorter and lighter than originals.

 

[Andy Higham]

The silencer to cradle mounts are a very neat solution. Much less visible than the front of engine braces I was contemplating