Breaking downpipes

It sounds like your engine is bouncing about in the frame more than usual. Are the isolastics shimmed correctly or are any engine bolts loose? Do you have the silencers held on with rubber mounts as it should be or have you fixed them with solid mounts?

Hi,

I have an 850 MkIII with non-balanced pipes bought from RGM about 18,000 miles ago. No obvious signs of cracking (dangerous thing to say just before heading off for the International).

You can get the balance pipes from:-

http://classicbikepartscheshire.com/shop/article_N65/Norton-Mk3-Downpipes-_-Balance.html?pse=apq

No idea what they are like.

Regards

Tony

I've not had this happen on my Commandos, but that actually surprises me! I think that the design is flawed. The only secure mount is where the pipe fits the head - everything else moves around. The rubber silencer mounts fail with monotonous regularity, increasing the amount of movement of the silencers (particularly if the heavier black-caps are fitted.)

So the pipes want to move, and this strains the fitting in the cylinder head. Little wonder that it either comes loose or breaks something.

One day, I'll make some brackets to connect the pipes to the engine/gearbox mounts, somewhere underneath the 'box. The pipes will then not be able to move at all at the head, but will be fixed with the engine/gearbox assembly.No doubt this will have some effect on the silencer mounts, but it would be an interesting project!

Hi Allan,

Seems the way ahead, and some nice little stubbie silencers that you can get for modern sports bikes would be ideal, cutting down on the weight hanging off the whole system and out of the way.

I have the original style flared ends and like others, my pipes have been fine for 17 years - looking a bit old now though.

Funnily this is the one part on mine that I've not been troubled with. When you bolt them up leave everything loose, just snug up the exh port nuts so the pipes are held in position, leave the silencer clamp loose and the rubber mount nuts then tighten from the head backwards. You may already be doing this of course! This way it all seems to find a happy unstressed position, well at idle or engine off!! Not had a breakage in 32k miles and the pipes are from Norvil (about 1999) though who knows who makes them for them.

There was a spate of breaking downpipes amongst some of the lads up here, some put it down to the wrong silencer brackets (The Mk3 ones are different and I suppose then so are the ones which supported the annular discharge silencers) Worth having a look round at the International, I'm sure there will be plenty to compare with!!

Downpipes, 750 type:

I can only speak for Andover Norton's offerings, so can not comment on what most others sell.

The "big lump" (flange) at the front is brazed in. Unfortunately, using a firm that has been making exhaust systems for decades did not save us from them coming up with some virtually unbrazed. In our first batch from this supplier these just had a layer around the joint, but nothing flowed into the gap between pipe and flange as it should have.

We have since replaced the pipes that fell apart f.o.c.- it wasn't all of them, but a small part of that batch.

This is now about two years ago, if not more, and all further batches since have been fine. I even dared ride my Commando to work this morning fitted with those pipes!

I know of one (pirate) supplier who used very light gauge tubing, and of these many just fell apart in mid-section, not at the flange. Not something you want to experience, as there is danger of the broken pipe digging into the road and acting like a lever.

Whilst Andover Norton operates a quality control system for incoming goods, this flange brazing problem was, unfortunately, a mistake that could not be detected short of x-raying the pipes, and at the time we weren't even aware there could BE a problem!

Downpipes, 750 type:

I can only speak for Andover Norton's offerings, so can not comment on what most others sell.

The "big lump" (flange) at the front is brazed in. Unfortunately, using a firm that has been making exhaust systems for decades did not save us from them coming up with some virtually unbrazed. In our first batch from this supplier these just had a layer around the joint, but nothing flowed into the gap between pipe and flange as it should have.

We have since replaced the pipes that fell apart f.o.c.- it wasn't all of them, but a small part of that batch.

This is now about two years ago, if not more, and all further batches since have been fine. I even dared ride my Commando to work this morning fitted with those pipes!

I know of one (pirate) supplier who used very light gauge tubing, and of these many just fell apart in mid-section, not at the flange. Not something you want to experience, as there is danger of the broken pipe digging into the road and acting like a lever.

Whilst Andover Norton operates a quality control system for incoming goods, this flange brazing problem was, unfortunately, a mistake that could not be detected short of x-raying the pipes, and at the time we weren't even aware there could BE a problem!

I'm amazed now that my Norvil pipes have survived, (probably about to break having said that). The chrome is rubbish but that just adds patina.

Previously wrote:

Funnily this is the one part on mine that I've not been troubled with. When you bolt them up leave everything loose, just snug up the exh port nuts so the pipes are held in position, leave the silencer clamp loose and the rubber mount nuts then tighten from the head backwards. You may already be doing this of course! This way it all seems to find a happy unstressed position, well at idle or engine off!! Not had a breakage in 32k miles and the pipes are from Norvil (about 1999) though who knows who makes them for them. ( never had one break in 30yrs)

Exactly what I would have said Keith, but also he needs to match his silencers to the correct silencer brackets. He doesnt say what silencers he is using ?? If the bike started life with 'black caps' and he's now got 'pea shooters' he would have to change all the brackets.

Possibly try fitting the exhaust pipes then slipping the silencers on and see where they want to sit in relation to the brackets fitted. Dont force them into position !