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MG Midget and Sprite Technical - 1500 exhaust manifold missing clamp

Hi everyone
I'd like your guidance (particularly from the 1500 owners) on something weird on our standard 1500 midget

At the end of last year I started to get exhaust blowing from under the bonnet, had a quick look and couldn't see anything wrong with the manifold so assumed it was the connection between manifold and exhaust - I fitted a new exhaust a couple of years ago

Getting ready for spring and MOT I had a good look today and am pretty sure that the leak is at the front of the manifold where it mates onto the block. The manifold itself seems fine, but I can't help but notice that there doesn't seem to be anything clamping the manifold to the block - you can see two large threaded holes top and bottom attached and Moss shows a clamping arrangement (106,107,108) for the top although nothing for the bottom.


Two questions - for those with 1500's - how does that clamping work, moss shows nuts not bolts and there's no sign of a stud, if you could have a look and see whats in the top and bottom holes that'd be great

and for everyone else any thoughts how this has suddenly happened ? I've no idea why these would be missing - I'm the only one that's done anything on this car in the last 20 years, and I suspect the last time those bolts would have been touched would have been when we put a new engine in in 199? - seems amazing to think it would have held without clamping for nearly 40k miles.

thanks for your guidance

tim



timmyk

There should indeed be studs.

Moss shows them on the cylinder head page - long and short.

Items 9 and 10. It looks like long on the top and short or the lower front.
Dave O'Neill 2

Top one should be a stud with an elongated oval spreader with ears to clamp both inlet and exhaust manifolds. Lower one should be a stud with washers and normal full nut.

The studs will have worked loose and vibrated out until they fell out. Check the others for tightness before they vanish as well!
GuyW

Is the left hand side not just handed ? are they still present ?

Likely need to replace the exhaust manifold gasket as that may well be damaged by the exhaust gas escaping.
richard b

thanks for your speedy responses - Richard, yes the left hand is just as Guy describes (although handed) - although the normal full nut is very deep - maybe 1 inch deep?

I checked all the others they're tight (worryingly tight if I have to replace the gasket)!

Anyone any idea what thread they would be - if the nuts on order are the same depth as the one in situ then they're going to be too long to double up to screw the stud in so I'll need to find some somewhere
timmyk

it should be like this


mark heyworth

Thanks mark

Normal nuts!
timmyk

Manifold nuts, though not necessarily on 1500 engines, were often of brass on older engines. Not sure why but think it may have been for the different coefficient of expansion so that they expanded towards the block faster than the stud lengthens as they heat up, maintaining tension onto the gasket joint.
GuyW

Right you are Guy - lots of them were brass and for the exact reason you mentioned. The 1500 manifold to head nuts and those clamping bridge pieces as in Mark's photo are of steel though.
However the nuts to clamp the exhaust to the manifold should be brass (or possibly bronze) and pretty deep. 3/8"UNF ISTR.
I have recently had to do a bit of research on this, but for the GT6 engine which has the identical arrangement.
By the way the clamp bridges and nuts are readily available. Rimmer Bros sell them, for example.
Greybeard

Thanks
All in order hopefully no more questions (or the next one is how do you undo siezed manifold nuts without oxyacetylene , but let’s wait and see for that one!

Actually one confirmation - the studs have a long and a shirt threaded end, I’m assuming short in the block ?
timmyk

just reporting back - all done without incident (& no need for a new gasket)

A couple of things, there are two different part numbers for the top and bottom nut and lo and behold the bottom one when it arrives is long - nearly an inch, so the same as on the other end of the manifold. the nut is steel not brass.

Also there are two sizes of clamps, this one needed the smaller of the two sizes, I think the bigger ones go inboard.

One question on my engine there are hex grub screws on the cylinder head when marks doesn't have them - any idea what they are for (if it helps mine is an unleaded conversion)

thanks for your help
timmyk

"One question on my engine there are hex grub screws on the cylinder head when marks doesn't have them - any idea what they are for (if it helps mine is an unleaded conversion)"

Possibly blanked off air injection ports.
R.A Davis

Your first photo shows one of the plugs directly above the exhaust port. Assuming that the others are also above exhaust ports, they will be for air injection, as R.A. said.

US models had exhaust port air injection for emissions purposes.
Dave O'Neill 2

This thread was discussed between 17/03/2019 and 23/03/2019

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