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MG MGF Technical - noisy SS front pipe blues

Since 3 days, my shiny Satur SS frontpipe died only after 15K miles. All that I noticed was in the beginning a soft rattling noise, but within hours the softness became harsh metallic loud noise. This morning at dealer we discovered that although the frontpipe is undamaged from outside (no, I didn't hit anything, thing still looks perfect) but you can feel the exhaust fumes coming through the flexible iron, but on the upper side only (need to put your hand between engine block and frontpipe).
Dealer concludes (logically) that the inside of the frontpipe is cracked, and due to heat crack becomes bigger (and louder).
(since hot exhaust fumes blow onto oil karter (sp?) dealer advised not to drive long or hard with it until it's fixed)

So 2 questions I have:

- is this a product fault? (Mike?). How else can I explain the pipe breaks down from inside only if there are no traces of collision at all.
- since I still have my original broken frontpipe (where the flexible iron thread woven around it is broken, not inside rubberish alike flexible part - see Dieter's site for picture) can I make 1 good frontpipe out of 2 broken ones? (dealer says no, due to assembly method)

Well, I ordered back a normal MGF frontpipe, at least that one lasted 75K miles before being ripped apart... :-
Dirk Vael

Interesting, I was at Donnington on Sunday, and wandering around the paddock with the MGF's. One conversation was pointed towards a well cracked exhaust manifold that was being replaced. The cracks were in the pipes and not at the flanges or welded joints. Oddly enough I was thinking about your previous experiences with overheated exhausts and there you go and pop up with exactly the same sort of problem, but just a little further down the system!

Looking at the cup cars pipes I see that the outer design may follow the same as the production cars, but the reality is that the welding is done on the outside rather than the inside. This means that these pipes have much greater flow area with no welding getting in the way.

Now if they crack pipes with a more efficient system then I wonder whether this is yet another symptom of the extra high engine bay tyemps we have been discussing elsewhere. I think it is as the same sort of cracks and thermal failures is seen on some exhausts that are wrapped in heat insulating material. I just wonder if the enclose nature of the MGF engine bay is sufficient to replicate the conditions found with insulation wrap. It may just be, and if so adds to the desireability to circulate more cooling air.

Rog
Roger Parker

Roger,

Maybe you can help me on this one. One particular hot day after driving my MGF hard, frequent near redlining for some tight turns sequences, I stopped the car to cool it down as the oil temp gauge was nearly in the red and noticed a distant crackling noise from the exhaust pipes (you know, that particular sound of very HOT metal cooling down rapidly). First time I've heard this from my F. Is this expected? And is this something I should be careful about in the future? Never noticed this on any previous sportscar.

Mike
Mike

Mike,
Your F shouldn't be "rode hard and put away wet". Don't stop an overheated car unless the water or oil is depleted. The proper procedure is to drive conservatively until the temperatures normalize then shut down. You will hear fewer noises and the engine will last much longer by avoiding thermal shock.
George B.

George, I should have clarified I didn't immediately stop and turn off the engine but drove on at lower revs for a bit to a rest area further down until the oil temp dropped down to 90ish.

On the subject of front pipe noises, could the rattling which I thought were original VVC tappet-related coming from a loose front pipe? Looked in the archives and seems earlier batches of F's had a problem with the original front pipe bracket. Would make sense as the sound is noticeably amplied when driving walls and barriers.. By the way, does anyone have a good clear photo online of the underside of the MGF showing the front pipe and exhaust connectiont?
Mike

Mike, my SP exhaust makes that noise all the time when I shut down, even if oil temp reached only 90. It's because of the thin stainless steel. With a standard exhaust it should still be noticeable aswell, but after 3 years of SP'ing I can't remember anymore if the standard thing was as noisy as the SP.

And if you drive the temp near red reduce speed immediately, if you drive along for more then 10 mins like that your headgasket will likely blow within 30 mins! (I had this once, thing went into red and I only noticed after trashing around for 10 minutes - reduced speed to cool back to about 120 but too late, a few kms further a puff of smoked ended the wild ride, despite the cooler oil temp)
For me 140° is really max temp, more than that means 'reduce speed'! K&N, SP & bypass tube help reducing temps aswell (about 10% I noticed)

photos of underside of F with frontpipe etc online at http://www.geocities.com/dirk.vael (check havoc section)
Dirk Vael

Isn't this downpipe immediately behind the plastic fuel tank ? I appreciate that there's a heat shield there - but how much heat would it take to melt the plastic tank, especially if it had very little fuel in it ?

Perhaps Rover fixed this 'problem', because I've never heard of it happening !

Steve
Steve

Re Reg's comment I've seen Cup Cars with the plastic cover of the alternator melted by the heat from the exhaust down pipes

jt
John Thomas

>Isn't this downpipe immediately behind the plastic fuel tank ? I appreciate that there's a heat shield there - but how much heat would it take to melt the plastic tank, especially if it had very little fuel in it ?

I assume you are worried that a fire could be caused if this were to happen Steve? If so then heat alone does not cause petrol to ignite - you need a spark. Still I would prefer this not to happen for any reason! :)
Paul Lathwell

Excuse my ignorance, but do these stainless steel exhaust systems use SS downpipes from the engine?

If so this could aggravate the possibility of HGF, since SS has a far lower heat conductivity than mild steel. Do all the people that regularly have HGF have SS front pipes?

Ralph
Ralph

Dirk, your old SP is still going strong (touch wood). Sounds like a beast when cold but still sounds nice when warm.

Andy P (of Scarlet fame) should be able to tell you all about the front downpipe, anyone seen him recently?
Tony Smith

This thread was discussed between 03/07/2000 and 06/07/2000

MG MGF Technical index

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