The Triumph Dolomite Club - Discussion Forum

Managed to change the failed gasket on the 1500 downpipe. The nuts came off surprisingly easily, which makes me suspect it has been done by the previous owner. Downpipe/gasket faces aren't distorted, mounts are done up, but I think it will fail again.

The old gasket hadn't twisted out of shape, it no longer existed, half of it had gone and the rest was like paper. Have no confidence in the next one lasting any better. So had anyone managed to mod this to make it last?

The gearbox bracket will help. I'm sure somebody suggested removing the studs and tapping the thread to a larger size and using a thicker bolt. I don't know if this would work on the 1500 manifold and downpipe.

They used to last about 18 months tops on my Spit 1500.....

so I went for the 4-2-1 stainless TT bits that sadly clash with OHV subframes.

You are stuck with it sadly...just buy the best OE quality ones you can find, keep the flanges flat and use brass nuts
and a plain and spring washer on each stud will be your best bet...

Jonners

We have a 4-2-1 manifold which will fit all the ohv cars which removes the need for that wretched gasket. We hope to find someone who can copy this manifold and put it into production one day.

Jon Tilson wrote:They used to last about 18 months tops on my Spit 1500.....

so I went for the 4-2-1 stainless TT bits that sadly clash with OHV subframes.

You are stuck with it sadly...just buy the best OE quality ones you can find, keep the flanges flat and use brass nuts
and a plain and spring washer on each stud will be your best bet...

Jonners

18 months, well at least it isn't expensive. Looking at mine my guess is movement causes a small leak, then the exhaust gases just corode the rest away. Much quieter with it on.

Anyway time to tune the rebuilt carbs, the idle is more stable now, just have to balance the damn things.

I fitted, without exaggeration, well over a dozen of these in 100k miles. Probably around a couple of dozen. At one point they were lasting 4 weeks and I could change one in 30 mins tools out to hands washed. In the end it was a cumulation of things that got it to the point they didn't fail. In no particular order:

- As already stated having absolutely flat mating surfaces is a must.
- If you have to change the manifold go somewhere like Wins when he has several in stock and choose from them carefully. The quality of overhaul jobs done is shite. 'Overhauled' is a blowover with some silver paint and change any visibly fooked studs. They don't routinely change all three, they never skim the face and if a thread is fooked to the point the stud doesn't sit straight - meh, whatever so long as it's tight. Whoever you get one from it'll be the same p155 poor job. I would for preference, should you need to, get one overhauled yourself by a local machine shop. It'll cost more in the short term but it's worth it.
- Call Wins and ask for a half dozen of his double length brass nuts and tighten them until they squeak and then some more until your nerve goes. I tried studs & steel nuts, studs & stainless nuts and bolts. Bolts probably last better but they tend to damage the threads on removal (most manifolds are helicoiled by now and bolts rip out the coil if they've been in any time). Steel nuts bring the stud out in quite a short time and stainless nuts were a total disaster.
- You can get the studs changed to the next size up but you'll need specially made nuts if you do. You have to get standard nuts drilled out and rethreaded as there isn't room for bigger nuts. I didn't do this, the double nuts were adequate.
- Having fitted a new gasket tighten again after the 1st heat cycle, again after a week and then whenever you're under the bonnet with a half inch spanner in your hand. You'll be surprised how much more you take up. The gasket always end up pancake flat as you found, you have to keep taking up the slack.
- Use exhaust gasket goo, copaslip and stainless washers.
- The gearbox bracket has already been mentioned, I concur on this and it needs to be correct.
- The biggest of the small differences I made was in fitting the original style exhaust clamp at the bracket. If you have a normal exhaust u clamp under there it will not hold the pipe in the correct spot. IIRC Chris Witor now has these in stainless. Change the bolt to stainless and add a half depth locking nut.
- You need to get the downpipe in the right spot and you can only do this with the rest of the exhaust disconnected, you need to do this if you change the manifold or when changing the clamp for the correct one. With the downpipe comfortable you can fit the exhaust to it. Once its set up right you can get away without disconnecting the exhaust every time but do a full reset if you change the manifold.

TLDR: Correctly overhauled manifold, correct gearbox bracket & OE clamp, double length brass nuts.

The original gaskets were made of a copper sandwich, with I suspect asbestos in the middle but I have seen replacement gaskets made from a modern material.

I have only used the original type so my question is do the more modern type last longer ?

Sometime ago I bought a large sheet of Klingersil C-4430 high temperature gasket material to experiment with on my 1850 exhaust manifold. If you would like a sample of this send me a P.M. and I'll put a some in the post to you.
The spec; of this material is on the R.S. Components web-site.
Tony.

Richard the old one wrote:
I have only used the original type so my question is do the more modern type last longer ?

No, the gaskets made from the silver material with dimpled surface are worse, by miles.