Short Flexi Downpipe - Two new replacements, two failures. Why? - Alfa Romeo Forum
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(Post Link) post #1 of 13 Old 17-07-16 Thread Starter
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Short Flexi Downpipe - Two new replacements, two failures. Why?

Formerly Knoppy1987 - but having troubles like a few others on passwords.

As the thread suggests, I had both downpipes replaced recently on my GTV 3.0 V6 CF2 and the flexi section on the shorter pipe is buzzing initially before turning into a full on noisy and horrible blow. The originals did not do this despite their age and I am scratching my head asking why I decided to treat her to some stainless downpipes.

The longer downpipe is fine upon inspection. As for the shorter pipe, I had a replacement under warranty at the garage I had the original fitted on Friday, drove to Camber Sands today only for the thing to go again (150 mile round trip). To be clear, it is the flexi section of the downpipe that is blowing towards to front of the flexi.

Before I get back on to the garage could they/I be missing something as I do not want to go round in roundabouts. The car is running nicely when the downpipe is initially fitted.

Any ideas appreciated or links to similar problems in various threads.
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I am having the same issue I think, although not on a GTV, but on a 3.2 166 (with CF2 exhaust manifolds).
First I got some aftermarket downpipes, and the buzzing/metallic like rattle was heard under havier acceleration (into the cabin as well if the radio was off) - I had the same issue on my previos car with alfa 3.0 as well.
Then I switched to custom made stainless equal length downpipes with stainless flexis as well, and this sound became ever more noticable.

In both cases flexis were made of three layers, where inner most layer was interlock, which I now think is what is causing these annoying sounds. Although this type of flexi is regarded to be the best as it can sustain the highest pressure, I now think it does not suite the engine very well.

Do you maybe still have your OEM downpipes? If so, please check or take a photo of the inside of flexi. So we can see which type they are using and then replace them with that same type.

There are three types of flexis: braided only on the outside, braided on inside and outside, and braided on the outside with interlock on the inside.
On my previous car I solved this issue by replacing the buzzing flexi with braided (inside and outside) flexi, if I remember correctly. But I have not yet found those to be completely made of stainless steel. If you do, please let me know.
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3.0 PH1 GTV

I thought i was the only one with this issue................................... my 18 yr old originals were finally in need of replacement so local AR specialist sourced some for me and they lasted 150 miles, second set a different manufacturer and they did same 150 miles also, and then the 3rd lot i am on now were better more expensive and ultimately lasted around 300 miles but these have gone now

same symptoms as you and its extremely annoying, Have on order a set of Cybox EL down pipes in hope this is the final time i this work gets done
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If it all seems under control..............your not going fast enough !!
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Thanks for the reply Lizard - unfortunately I do not have the old flexi. Annoying as I had a spare set from a CF3 knocking around that I sold - could have checked with those.

It is one of the first jobs on the car I entrusted to a garage and I cannot fathom, why, after 50 miles, the buzzes before eventually sounding like a Fog Horn. Other than the part being duff of course. But why just the shorter of the two downpipes?

I am trying to find out who the supplier of the part was from the garage so maybe I can ask them what you have prompted me with. I actually watched the first part being replaced and to the naked eye, it looked as though it was braided on the outside only. The reason I say that is because when they took the part off and I seen the damage (a hole, brown burn marks etc. at the start of the flexi section) and I saw no evidence of anything internal or beyond that initial layer.
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(Post Link) post #5 of 13 Old 18-07-16 Thread Starter
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Originally Posted by bradpit999 View Post
3.0 PH1 GTV

I thought i was the only one with this issue................................... my 18 yr old originals were finally in need of replacement so local AR specialist sourced some for me and they lasted 150 miles, second set a different manufacturer and they did same 150 miles also, and then the 3rd lot i am on now were better more expensive and ultimately lasted around 300 miles but these have gone now

same symptoms as you and its extremely annoying, Have on order a set of Cybox EL down pipes in hope this is the final time i this work gets done
It is annoying as you cannot drive the car as it should be driven - it is a race to sixth gear to keep the noise levels to a minimum at the moment. The there is the smell of fuel in the cabin.

I hope all those sets you have been able to send back and claim back.

I would be interested to hear how you get on with the latest set. Keep me posted.
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Presumably you have all checked the engine/transmission mounts to make sure none of them have sagged? Because if they have, a new flexi pipe will be taking most of the strain as the engine twists on accel and decel.
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Presumably you have all checked the engine/transmission mounts to make sure none of them have sagged? Because if they have, a new flexi pipe will be taking most of the strain as the engine twists on accel and decel.
Thanks for the feedback Pud.

I know that my top mount could probably do with being replaced and I will definitely check the others. Sorry if the question is a daft one (call it myself being less mechanically minded/illogical), if the new shorter flexi is succumbing to engine twisting etc. why would the original not succumb?
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If your top mount is knackered then you probably have a sagging rear engine mount (diff housing to subframe) too which 'pulls' on the flexi and tries to pull the whole exhaust system towards the front of the car. I imagine due to production variables the shorter downpipe is under more tension than the longer downpipe and that is why that one is failing first rather than the long one sometimes failing too.

Not all flexis are equally flexible, OEM ones tend to be much better than aftermarket.
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Between different types of flexis (which I mentioned before) the flexibility differs as well. Flexi that is braided on both sides is the most flexible of them, and if I remember correctly OEM are of this type.

@Pud: my upper engine mounts are new and bottom suppose to be in good shape. Anyway, do you maybe know where to get stainless flexis (including stainless end caps, not just flex part) that are braided on inside and outside? Ebay search was not so successful. Thanks.
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Thanks again all - I will investigate the pointers above and let you know how I get on.
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Thought I would return with my feedback as it may help others starting out (probably not experienced folk) and changes were relatively simple. Another GTV learning experience for me to a list that is getting longer and it was satisfying (for now).

Anyway, I had the car up on stands yesterday so I could get a good look at what was going on when the car was started and just for access more than anything. I also had the mounts off. Good news, both were actually fine. As I had bought a powerflex bush for the top engine mount I replaced it. Not so good news, when going to remove the rear mount, whoever checked/had it off previously had not secured it - one of the bolts had just been screwed in by hand half way.

With a good friend helping throughout (BMW Youtuber Elbow Grease), we had a look and it was quite obvious there was too much movement in the mid-section of the exhaust including the CAT. There was a bush in the middle of the car, nearside that was perished and causing a lot of movement. Some more of the exhaust bushes were perished. Several exhaust bushes/hangers (some creative because of availability) later, mounting points off and cleaned, car started, the difference was noticeable particularly when idling, when up to temperature and applying throttle. Everything secure meant that the Flexi's were not all over the place especially when applying throttle.

I went out for some low gear, high rev GTV/Busso fun and so far, so good and no signs of early squirming or buzzing that had been common from the off before. Even better, I went over Hampton Court Bridge and in traffic, I was approached by a couple through the window who told me that I have a very nice car. I may just get a stress free Sunday drive out of her today as well!

Still having paid a garage 300-400 to sort out the exhaust, quite disappointed that this was not diagnosed, seen or even advised.
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My 3 after market downpipes have lasted between 100-300 miles before starting to blow, its in this week for a full proper check over to include the gearbox and engine mounts, As well as top mount, having looked on top mount one end is powerflex other end is perished rubber ???? .......................hopefully this is final last and permanent fix
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As my car has good engine mounts and exhaust rubber mounts are in good condition as well, I knew that problem must lie elsewhere.
Today I was having made custom stanless cat section, and while standing under the car I came to an idea that flexis might already be "flexed" when engine is turned off or not under load. And when pressing the accelerator they would flex over their limit, resulting in buzzing/rattling noise.

Basically this means that the guy who made me custom downpipes, welded in flexis in a way that they were flexed when the engine was not under load.

So today when cat section was being made I tried to set the flexis in as neutral position as possible (meaning straght) when taking measures, and after first drive I think it worked! There was no more buzzing sound, let that be under full acceleration with windows opened, or revving the engine when standing still - in both of these cases strong buzzing sound was present before. More testing will need to be done to make sure it is ok now, but it looks promising.
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