Exhaust crack near cylinder head

Mark, not seen this before although mine did lose a piece at the end, on the flange on the R/H pipe.

Mine is a MK 3 and no room for movement on the L/H pipe. I'm wondering if the balanced pipes offered more strength / support?

Previously mark_oliver wrote:

I have enclosed some pictures of the issue, I bought the exhaust from armours and they repaired it in the first week. and for a 18 moths it has been fins but recently it has cracked and i had it repaired locally but it cracked a week later just above the repair. The lining insde the pipe does not go to the end as it used to in the old pipe and i wonder if this is an issue? or possibly the material , stainless steel is not good for exhaust use. Any thoughts would be appreciated.

Mark, many moons ago when I was racing two strokes in the MGP, we where always having to weld ex pipes, expansion chambers etc,eventually some wise head said why not try brazing, it will stand the vibes better than a rigid weld, and it did, maybe if you have time you could try that approach, regards. Jim hill

Previously mark_oliver wrote:

I have enclosed some pictures of the issue, I bought the exhaust from armours and they repaired it in the first week. and for a 18 moths it has been fins but recently it has cracked and i had it repaired locally but it cracked a week later just above the repair. The lining insde the pipe does not go to the end as it used to in the old pipe and i wonder if this is an issue? or possibly the material , stainless steel is not good for exhaust use. Any thoughts would be appreciated.

I have spoken at length to my welder about this kind of thing. His explanation is that the metal gets brittle right next to the weld. If it were possible to normalise the stainless it would make it less prone to cracking but I can't speak to that particular grade of stainless you have. You may be able to braze it but most stainless needs heli-arc or TIG and nothing else will work. I am not a welder myself but I had so many repairs to make (head and barrel fins, exhaust, etc.) I was forced to buy my own TIG welder just to make it affordable. I can't just hand over my pay check to my welder.

Brazing will stand up to vibration better than welding. I brazed the top front bracket on my Commando oil tank after the rubber mount failed and the bracket broke. That was more than 20 years ago and the repair still hold good. (And the rubber mount)

Never heard of brazing stainless before but if it can be done then please do tell.

no as far as i know you can not braze stainless steel ,i had the same problem as you on my 750 commando with stainless down pipes i am a welder by trade i tig welded mine 5 maybe 6 times each time it broke always on the left side in the end i went back to chrome steel with no more problems cheers nick

As Jonathan has mentioned .....the most likely cause of this breakage is brittle weld failure. It was a big problem in WW11 when the Allies tried to build ships more quickly by welding plates together for the hulls. Variations in temperature and viabration are the main causes of this type of weld failure.

Brazing would probably be best but ............Have you tried using disimilar metal welding rods with an ARC set. The claim is that these high Nickel content rods will weld anything to anything. I have just used some to fix a steel peg onto the foot of my Dommie main stand and also re-attach two fins to a 650 barrel.

The flange end on my Commando exhaust broke off a few years ago. My local welder repaired it for £20 but I bought some spare pipes just in case it failed again. It hasn't yet, but.......it occured to me that this was a stressed area due to the movement of the engine. Consequently I have made sure that, at the silencer end of the system, the rubber mounts are carefully positioned so that they are central to any silencer movement. This allows engine and the pipes to move about quite a lot before the are yanked or, pushed or pulled.