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MG Midget and Sprite Technical - Standard Metro head. Any good?

A freind of mine blew his head gasket last weekend and as his engine was scheduled for a rebuild anyway, he wasn't too upset. he has been offered a standard (Not MG) Metro head, so the question is, would it make great deal of difference if he fitted it to his standard 1275 engine ('73 car) during the course of his rebuild.

Bernie.
b higginson

is he proposing to fit the head 'as-is' or is he having some work done on it?
David Smith

Hi Dave. I think he may have it unleaded, but I don't think it's going to be flowed or ported.

Bernie.
b higginson

It should be unleaded!
And in unported form be no less than a normal 12G940 from a later midget.

Onno Könemann

I didn't know that they were unleaded from the early cars and I don't know what year it is. I suppose if he bought a new water pump it would do away with the bypass hose, but are there any other advantages to be had by fitting it unmodified?
b higginson

The early Metros were not unleaded I understand and Metros were not unleaded in production until the change of filler cap position from low in front of the rear wheel to the higher than the wheel arch version.

The higher filler cap also had the "use unleaded fuel ONLY" "95 RON" sticker inside the filler flap.

Someone is bound to be along with the date of the changeover soon.

The head is fine to use even in standard form as far as I know and similar to 12G940 as per Onno's post but not necessarily unleaded.
Bill 1

Only as a matter of interest, how long would an unleaded head run before the seats gave out? 100 miles, 1000, 10000?
Lawrence Slater

More
Hardend inserts are needed with soft aloy heads.
With our harder cast iron heads it is only a mild improvement.

My 998 mini had done more than 30000KM on unleaded and showed no signs of disastrous wear.
With a slight hand grinding it would have been as good as new (but it was discarded for faster)
Onno Könemann

Lawrence,
I think that's one for an Archive search as I can remember much talk of this going back to my previous Spridget - ETA as usual Onno posted whilst I was still typing

Bob,
I'm probably wrong but the unleaded petrol only sign was it more to do with the "new cat" - persumably leaded heads(?) might have been at the same time
N Atkins

Thanks both. If that's the case, when I re-build my spare engine, I might simply regrind the valves then. I haven't stripped the head yet, but if the valves are good, maybe I'll save myself some pounds.
Lawrence Slater

If it is all apart and it is for a spare engine (ie no time pressure) why save that few quid?

If it is running it is not worth the hassle but if you have the chance then why not build the most durable engine you can?
Onno Könemann

Hi Onno,

Yeah I guess your right, but I'm only rebuilding the engine as spare for the one in the car, and that still has many many 10s of thousands of miles left in it.

So with advancing age, I might be dead or disabled long before I get to do 30000 miles on the spare rebuilt engine. lol. And given the poor state of affairs for pensions over here, I might need every penny I can get in my care home. LOL
Lawrence Slater

Personally, I'd spend the money. My machinist charged $10 labor and $5 for the seat (American) per exhaust valve. He said that work, along with a light skimming and new stem seals, is all she'll need for another 40-odd years.
JM Young

measure the valve sizes! if it's from a 1.3HLE IIRC they had smaller valves to get the economy? or was it all in the cam? certainly not all 12G940s have the same valves...
David Smith

I've never seen a standard 1275 Metro head with anything other than 33 x 29 valves or 35.5 x 29 on MG Metros. They are also numbered as 12G 940 despite the slight casting differences. They are interchangable with the earlier head...
James B

Metro Turbos had sodium filled exhaust valves and therefore thicker stems...
James B

I think the HLE economy was certainly, in part, due to very tall gearing.
I don't know if there was any difference in camshaft.
Dave O'Neill 2

Lawrence the conventional wisdom as I understand it is that the faces of valve seats that ran with tetraethyl lead petrol have generally been pretreated and can expect a reasonable life before(/if) recession sets in.

Better if Peter or Debs comes in on this I s'pect.

If you then grind away at the valve sealing faces it will remove the protection layer which is probably microns thick if at all, then you will have no lead protection remaining.

Hope this makes sense, means I will not be grinding in my valves when the engine comes out for maintenance.

Nigel I have been told that the heads were given hardened valve seats at changeover time, have you been advised differently?

As the changeover came during my AA career and using unleaded petrol was a seriously worrisome affair at the time, I'm certain "Austin Rover MG Co Ltd Inc" sent out relevant data packs on the topic to garages and the AA.

I will have to delve around in my old paperwork to see now you have raised a new spectre for us.

Bill 1

Hi Bill,
no I'm not sure what what I was told, whatever it was I've forgotten (long ago) - I just remembered that on some cars at change over year(s) had stickers as cats were new to us at the time and some cars could take leaded or not whilst others had a cat so unleaded only

(I think, IIRC)
N Atkins

Thanks Bill. I've got some old lead plumbing pipe I pulled out a while back, and haven't sold yet. Maybe I could just shove a length in the tank LOL.

Lawrence Slater

if you have the head on a bench, you can inspect it for inserts under a strong light


Norm
Norm Kerr

But, to get back to my original question, would there be any advantages in fitting the unmodified Metro head over the 1275 head he already has? If not, I guess he would rather keep his original head.

Bernie.
b higginson

No advantages other than that it might be unleaded and might have less work done in its life
Onno Könemann

I think they were only unleaded from 1990- onwards,
Cheers John
HALL JOHN

Thanks guys. At least now we have something to go on. The reason I've been asking the questions and not him is, he works abroad a lot so is not always available.
Thanks again.

Bernie.

b higginson


Following on from this, are the heads from the later SPI and MPI minis useable? Can't see any obvious differences apart from the obvious bypass hose, but are there less obvious variations?

I need to do some investigation at the weekend but I suspect I have a valve that's burnt and was wondering about the option of a low mileage MPI head vs a recon...discuss

Cheers!
Mark
MarkH1

This thread was discussed between 05/11/2011 and 09/11/2011

MG Midget and Sprite Technical index

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