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Broken Exhaust Header

Moss Motors
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Shelby1115 Avatar
Shelby1115 Robert Kaylor
SHELBY, NC, USA   USA
Headed to work this AM and cruising along smoothly and then suddenly my 78 B starts sounding like its about to blow up or something. Get pulled off to check things out. 1st thing I notice is the portion of my exhaust hanging underneath. Looks like the portion of the exhaust broke between the resonator and the muffler broke just behind the resonator. So no big deal.

But upon further review. I pop the hood to make sure everything under there is okay and discover that it also broke the exhaust manifold off at the front as well.

So now I'm looking at needing to replace the exhaust and the manifold. But I cant find the exhaust manifold listed at any of the usual sites (Moss, VB) .

So what are my options running a Weber 45 MCHH.

Can I strictly run headers to the new exhaust.

Or am I going to have to track down a manifold or try to have the current manifold repaired.

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ohlord Avatar
ohlord Gold Member Rob C
North of Seattle, N.W., USA   USA
1957 Land Rover Series I "EYEYIYI"
1971 MG MGB
1971 MG MGB "Bedouin 2"
You won't get the cast iron manifold repaired.
And they are no longrr made
Buy sell forum or stainless header moss bell etc



"I'm a long way gone down this wild road I'm on
It's gonna take me where I'm bound
It's a long way around"



"These are the days that must happen to you"

RD2 Radar/ Electronic Warfare Technician
Vietnam 1969-1972



Edited 1 time(s). Last edit at 2018-02-13 12:17 PM by ohlord.

Chalky Avatar
Chalky David White
Coventry, Warwickshire, UK   GBR
Try eBay. Cast manifolds turn up very frequently. Postage to the US may be high but they’re easily available.

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Be Coming Avatar
Be Coming Kelvin Dodd
So. Calif., USA   USA
Robert.
The first thing to do is identify which manifold you have. With a Weber 45MCHH, I'm guessing you have the stock original combined intake/exhaust manifold as used from 1975-80 Federal cars.

Take a look at some diagrams and identify what you have. The original late manifold did have a tendency to crack at the front where it turns 180 degrees to the catalytic converter flange. There was an updated version that had a strengthening rib added and that would be the one to look for.

Kelvin.

Shelby1115 Avatar
Shelby1115 Robert Kaylor
SHELBY, NC, USA   USA
Rob,

i think the intake/exhaust are combined with the Weber 45 MCHH. So would I still be able to run a straight header?



Edited 1 time(s). Last edit at 2018-02-13 01:37 PM by Shelby1115.

Shelby1115 Avatar
Shelby1115 Robert Kaylor
SHELBY, NC, USA   USA
Kelvin,

Im pretty sure youre correct that the 2 are combined. And where it broke is exactly where youre talking about right where it makes the turn. but so far no luck locating anything anywhere. so not too sure what Im going to do if I cant locate one

Be Coming Avatar
Be Coming Kelvin Dodd
So. Calif., USA   USA
Robert.

Put out a request for a 1975-80 intake/exhaust manifold in the Buy, Sell & Trade forum. There are a bunch of these out there that have been taken off de-smogged cars. I've attached an image of the replacement type that had the reinforcing rib. If you can find one, this is what to get.


The other option is to ditch the 45 MCH and go with either a Weber DGV which requires a separate exhaust manifold, or convert to original type twin SU carbs.

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Attachments:
Late Manifold with rib.jpg    16.9 KB
Late Manifold with rib.jpg

ClayJ Avatar
ClayJ Silver Member Clay Johnston
Mt. Olive, MS, USA   USA
1972 MG MGB
I agree with Kelvin, quickest/cheapest fix would be to locate a secondhand combo manifold. Shouldn't cost much at all.

If you're happy with the performance, a second option would be to cut the intake manifold off the combo unit and use that for the intake. I've heard of this done but never done it myself. Then you would need either a header or a earlier exhaust manifold. Either of these options are going to require some exhaust pipe work and some trial and fit.



Edited 1 time(s). Last edit at 2018-02-13 03:30 PM by ClayJ.

geezer Avatar
geezer Silver Member charles durning
Magee, MS, USA   USA
1958 MG Magnette ZB "Chick Magnette (sold)"
1967 Morris Minor 1000 Saloon (2-door) "Marvin"
1974 MG MGB GT
Actually a skilled welder can repair the manifold. Emphasis on SKILLED. There are folks who specialize in repair of broken castings. My first reaction would be to cut off the intake manifold and then find an earlier MGB cast iron manifold. It's been awhile since I've seen a combo manifold so not sure about clearance between the intake and the center branch of the early exhaust manifold. But, hey, what have you got to lose?



Who's version of right are we talking about? When you get 10 LBC owners in a room you'll get 12 different answers.

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Be Coming Avatar
Be Coming Kelvin Dodd
So. Calif., USA   USA
I have not personally tried it, but I'm pretty certain you cannot remove the intake portion of the manifold and re-use it. The back wall of the intake is shared with the exhaust, so there is no room for another manifold.

What can be done, which may be confusing people is the intake portion removed from the exhaust casting. Then an SU or other intake manifold can be used with the stock catalytic converter location. See images below.

Kelvin.


Attachments:
P1250029.JPG    70.7 KB
P1250029.JPG

P1250030.JPG    59.9 KB
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Steven 67GT Avatar
Steven 67GT Steven Rechter
Imperial Beach, CA, USA   USA
If you don't need to keep it original for smog testing and you want to keep that Weber, you should be looking for an Austin Marina manifold.

The Marina manifold uses a single carb and flows much better than the 75-80 manifold. Much like the earlier manifolds.



There are no bad days at the beach.


Attachments:
austin.jpg    36.1 KB
austin.jpg

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