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Manifold to exhasut downpipe gasket keeps blowing!


jlo1986

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I have a spitfire 1500 with the above recurring problem- I keep replacing the gasket between the manifold and the downpipe and it keeps blowing after about 200 or so miles- does anybody know why or have any solutions?

When I fit it I use some paste as well and tighten the nuts as tight as I can get- I have to use a spanner as I can't seem to get a socket onto any of the nuts. Am I doing something wrong?

Any help would be great as this is beginning to drive me mad!!!

Thanks, Jamie

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On the contrary, brass nuts are the correct item.
Steel ones corrode to the studs and you'll end up with breaking one - a b*gg*r to deal with.

Have a look at the rubber engine bearing blocks.  If they are perished, the engine may be moving about a lot.

John

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The missing front exhaust mounting is mentioned elsewhere as helping the joint to last. But the design is known to be flawed, and as above either a 4 branch manifold or use a spitfire/herald 1300 cast iron exhaust manifold and matching spit IV frontpipe. Problem solved.
Also would agree that paste is not a great idea, a qulity gasket and get the joint good and tight is helpful. The brass nuts are correct, but often the studs are not great. O have had moderate success by drilling broken studs out and using a high tensile bolt.

Cheers
Clive

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Brass nuts were NEVER used by the factory. I'm not saying they are a bad idea, but they are NOT "the correct item".
The exhaust mounting to the gearbox acts as a fulcrum, without it the flexing occurs along the entire length of the exhaust system, rather than locally. Our Dolomite 1500 blew it's downpipe gasket every 3000 miles, or every 3 months, whichever came sooner! With this mounting removed, the car completed 5000 miles without incident until it was sold, still running nicely.......
Ultimately, the design is poor. A tubular manifold is the proper fix. Failing this, make sure the mating faces are properly flat, and use new studs. DON'T use any exhaust paste, this will only fill gaps which shouldn't be there in the first place. Steel nuts will allow higher torque to be applied if necessary, brass ones often strip their threads. Make sure engine and gearbox mountings are in good order, some repro mountings use horribly soft rubber, which allows the engine to move about all over the place.
Cheers,
Bill.

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I am going to fix mine this weekend exactly the same problem i have got new studs and nuts to put on and am  going to slide a very thin stainless tube inside the exhaust at the joint as an extra protection , will let you know if it works

BAZ

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Bill,
I think you'll agree with me that there is a difference between the 'correct item it left the Triumph factory with' and ' the correct item that Triumph might have fitted if they hadn't been broke half the time and obsessed with bean counting'
John

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With a weak spot like this, I am not convinced that fitting a soft metal nut is the best solution. I'm uncertain what the intended torque figure is, I'm equally uncertain what torque the brass nuts will withstand. New studs and steel nuts tightened as much as physically possible may be the best solution......
I am open to being convinced otherwise, try me!
Cheers,
Bill.

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Stainless may be good. Have used stainless nuts and bolts on a manifold I had to drill out, worked a dream. Not original of course, but in some respects better. I guess if new decent quality studs can be fitted they would be pretty good too.

Clive

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As I recall from my days as a main dealer mechanic in the mid 70's a lot of manufacturers used brass nuts on the exhaust and manifiold. These included Hillman, Vauxhall, Datsun and even BMW. I think the idea was that they did not rust out so quickly and the electrolytic corrosion was minimised.  I just used what was already there!

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Bill,
Bowing to your experience, mine is that 'soft' brass nuts on the exhaust manifold give no problems from the stresses of racing.  And as phil points out, they are specified as O/e for this application by many manufacturers.  I'd add, from those alive today, Subaru and VW.  Also, I believe that MGBs left the factory with brass exhaust manifold nuts!

John

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Thanks for all the advice guys.

I've had a look at the mounts and they do look a bit squashy- not that I have anything to compare them against! The engine is coming out soon anyway so I’ll put some new ones in when I put it back- anybody got any advice as to where I can get some good quality ones as people have mentioned (and I have heard in the past) that some are a bit rubbish.

Cheers

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JohnD wrote:
And as phil points out, they are specified as O/e for this application by many manufacturers.  


I've no argument with that, I generally use brass nuts on my own cars. The 1500 downpipe however is a crap design which needs all the help it can get. I am merely suggesting that in the case of this particular design, using the strongest possible components and torqueing beyond specified figures MAY help with longevity of the gasket.
Cheers,
Bill.

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all the race engines I used to deal with including ALL the high performance go kart engines use brass nuts exclusivley for the exhaust systrem.  I think this is partly an insurance policy against damaging studs and castings by overtorquing or trying to remove a horridble seized nut.  The main advantage being the bloody things dont seize on like their steel counterparts, the hea\t and water exposure an exhaust get really aggrevate this.  

I wouldnt have thought doing to things up to some huge torque would necessarily be good anyway, you might distort the masting faces causing the unsupportred bit between the bolts to bow open

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A problem that does not seem to have been mentioned with studs is the rusting of the thread exposed beyond the nut.  This rust makes removal of the nuts difficult and in the case or brass nuts cut the treads deeper ruling out re-using them.
It is also not uncommon for these studs to break off when trying to remove nuts from coroded ones.  The stainless suggestion would be helpful here but most readily available stainless nuts and bolts are quite soft.
If the manifold design allows I have always drilled out the studs on older engines and fitted high tensile bolts which can be cut off if future corrosion causes problems.
On the Spit ("Mk 1") one side of the head of the bolt has to be removed on the inner bolt.    
Well designed brass nuts that are long enough to cover all the thread and only fitted and removed with the correct size ring or socket are satisfactory with new studs but I still prefer bolts if possible.

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Hi, I have replaced the engines in both my 13/60 estate and J.C.Midge with 1500 items, I did the Midge first, and had nothing but problems with the manifold/down pipe joint. On the advice of I can't remember who, I fitted the 1300 cast manifold, and in at least 5 yrs have had NO problem. So when I fitted the 1500 into the Herald, I did the same. 2 1/2 yrs, no probs. Cheers, Mark.

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