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MG Midget and Sprite Technical - Exhaust Manifold to Engine Block Problem

Hi
Help needed from all you gurus out there.

Mk 3 midget 1275 standard A series.

Took carbs off etc as I have a leak from the exhaust manifold and could not figure it out. How do I know I had a leak? By blocking the end of the pipe with the engine running you could see and feel it coming out but hard to see where. Also smell of exhaust was apparent.

I thought I would have a hard time removing the nuts etc from the manifold but they were pretty loose. The second vent from the front showed signs of blowing but the gasket seems OK. How tight should they be?

The manifold looks sound although the heat shield is cracked and I will weld that shut again.
Cheers
Dave
Dave Price

it is pretty much impossible to get a torque wrench in there (it is really hard to get any wrench on those nuts), so it takes a bit of care to make sure that you get them properly tight. Here's what I do:

use a new gasket, and make sure that your intake and exhaust manifolds have the same thickness where the clamping washers go - if there is any difference, either grind down the high one, or make a stepped washer, so that the force is equally distributed over both when the nut is tightened

use the tall, brass nuts (for ease of removal later, the brass won't rust, and the tall size makes up for the softer material by using more threads), and tighten them all as evenly as possible

if I remember correctly, they are 5/16-24 studs, so the torque for them would be 19 ft-lbs (dry) / 11 ft-lbs (if liberally covered with anti-seize)

use a torque wrench on the end two (the ones that you can get one on), and then feel how tight that is with your hand on a spanner, and then go for that same feel on the middle 4


Hope this helps,
Norm
Norm Kerr

I find it a real pain to get the longer brass nuts on in the very restricted area of the manifold and as stated the normal sized brass nuts do not have the shear strength to do the job.

I therefore use stainless steel nuts in this application.

With everything involved with our cars the world has gone torque wrench mad, unless it is head bolts or such throw the damn thing away. Have you ever noticed that as the spanner size increases 1/2, 9/16, 3/4 then the length also increases? well they are designed to allow you about the right amount of effort for the bolt/nut size you are doing up.

These manifold bolts need to be tight. I do them all up in sequence from the middle out/either side. I keep doing this sequence a number of times with an 1/2 inch combination ring until I can bearly tighten them any more. (if I were to use the brass nuts they would strip. Using this technique they tend to remain tight, if you casually tighten them up I have found a few weeks later you will have a manifold leak and one or 2 nuts would be fairly loose.

I also smear exhaust assembly paste on the exhaust ports of the gasket to help sealing. I have found this to be of benefit also, the stuff bosal supply is great.
Bob Turbo Midget England

Bob,
I have only just read this thread with your comment on spanner sizes! See my parallel thoughts on tightening back axle u bolts !

Part of owning a car of this sort is to squire the skills appropriate to the design and use of the right tools to go with it. Traditional spanner sizing is one of my long held fixations! They are not the size they are purely by accident!
Guy

I use these - brilliant. Smaller nut easier to get a ratchet spanner on as well.
http://www.minispares.com/Product.aspx?ty=pb&pid=37256&title=
John Collinson

x2, Guy on aquiring the skills for working on specific cars. Each is different, and the inlet/exhaust manifold on a A series spridget, requires some contortion of the hand. I've even bent an open ended spanner for the purpose. I use a combination of, adjustable, ring, and open end.

x 2 Bob on don't bother with a torque wrench. Tight is tight enough as long as you get it even as poss, and work centre out.

I use the plain steel nuts, as I too used to strip the brass ones. Mind you I never tried the extra long ones.

Lawrence Slater

I've never found the need for a torque wrench on the manifold nuts; never needed to use stainless steel studs or nuts; never needed to use exhaust goo (assembly paste). Just use the correct quality gasket, ensure the surfaces are flat and clean, and use 4 deep brass nuts on the centre studs and two steel ones on the outers, exactly as it left the factory. I have a reduced-jaws open-ended spanner that fits OK; if you strip the threads on the brass nuts you need to practice until you don't!
David Smith

Ok - if I go Stainless - the thread is???
Dave Price

The long brass ones are another of my favourite finds. Never had any problems with them stripping and they cover all the thread so no rust which means easy removal. The extra length helps with getting to the two centre ones as well. Obviously it depends on what manifolds you are using, mine are Metro inlet and Maniflow exhaust.
John Payne

My manifold is currently held on with nan assortment of whatever nuts I could find that had the right thread. But I think the brass nuts are also specified because as the manifold and studs heat up and expand, the brass nuts also expand, but being brass, they expand more and in effect this increases the clamping action.

Guy

Ey up smiffy never had you down as a concours nut!!

"""exactly as it left the factory""

You will have to post a picture of your "concours" car then!! LOL
Robert (Bob) Midget Turbo

Well Bob, I've noticed the early Spridgets, Minors, 1098 engines mostly, had all brass nuts, but most of the 1275s had these 2 steel outer ones; I respect Abingdon's engineers and reckon there was a reason for it, so I stick with it. Bear in mind I'm not an engineer so cannot argue the case for anything different (and not having manifold sealing issues, don't need to).
David Smith

One thing to keep in mind as you deal with an exhaust blow at the manifold - be sure to check the manifold mounting faces with a good straightedge before remounting with a new gasket. Several years ago the gasket on my 1500 burned through at the bottom of the center branch, and when I checked things out with an edge I found that there was a definite gap at the center branch when I checked across the faces, sufficient that the center branch was never going to seal well unless I did something about it. So I took both manifolds to a local engine shop and had them skimmed. See photo below. It's been fine ever since. I know yours isn't a 1500, but I'm sure this still applies.

By the way, I seem to remember that the recommended torque for the mounting nuts was 22 lb. ft. But as mentioned above, if your mounting is anything like mine, your NEVER going to get a torque wrench on some of those nuts. The lower ones on the 1500 are nearly impossible to get to with a simple spanner, let alone a torquer.

By the way, the nuts on my 1500 are brass.

-:G:-


Gryf Ketcherside

This thread was discussed between 28/11/2011 and 01/12/2011

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