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MG Midget and Sprite Technical - cylinder head identification

I have a cylinder head from a 1971 Austin Sprite 1275. It has 2G94 cast between two of the holes in the head. It also has 12G938 punched into the flat area beside the thermostat. Does this sound about right for the age of the car? I believe it to be original. I shall be putting it in the classified section so want to check it's spec.
Steve Church

Sounds like a 12G940
The normal 1275 head with 1 5/16 inlet and 1 5/32 exhaust valves and a 21.4 cc chamber.

Don't know about the stamped nr though...
Onno Könemann

I found this on a Mini forum:

"The 12G938 was a special casing of the 940, just for competition. It had a thicker deck and extra metal around the ports to allow better ports to be ground, without the fear of breaking through."

I don't know if thats true or not though.
Steve Church

And I knew the numbers sounded familiar!
Onno Könemann

I thought that 12G938 was revived on some A+ heads?
D O'Neill

Yepp.. i want to say it was a special works head... Not many made, but im reaching back thur some serious cobwebs in tthe ol hat noodle

It was a pre cursor to the mini cooper A+ head that had the bigger valves...


Prop there is no thing like a mini cooper A+ head...
The later 90's coopers had a normal 12G940 heads
Onno Könemann

Check out this link. Choose number 13 in the list for the 1275 CooperS head. 1275 Coopers Cylinder head Identification.

Lawrence Slater

I have seen a few with that number stamped on them - I wasn't aware it denoted anything significant - my recollection is that they are exactly the same as any other 12G940 head -

12G940 heads fitted to 1300GT and later Cooper S have 1.4" (35.6mm) inlet valves and 11 stud holes - MG Metros had 1.4" valves and 9 holes - everything else ran 1.3" (33mm) inlet valves and 9 holes but the castings were all exactly the same (give or take a bit of shifting in the sand cores). I have not heard anything about a special run of heads designed for modification but knowing Special Tuning its possible...

12A185 and AEG163 heads may seem like a good idea, but if you have one in good condition sell it... The originality fascists and FIA Mini guys will probably give you enough to buy a fully modded 940... They are also to be avoided because they are very prone to cracking

James Bilsland

1300GT and late Cooper S were also stamped '12G1805' by the thermostat housing.

12A185 is a bit odd as there were two completely different castings with the same number. One for small bore engines - 997 Cooper and some Frogeyes ISTR - and one for Cooper S.
D O'Neill

I have a 12A185 if anyone is interested.
The head was skimmed .040 to put the head at 2.710. The intake valves off this head measure 1.51. I do still have have the valves that will go along with the head. It's on eBay right now.

Jon Saylor

Hi Jon,

What engine is that off?

If the inlet valves are that large, what size are the exhaust valves? How you experienced any cracking between the seats?
Lawrence Slater

That is a head for a small-bore engine and I would imagine that the inlet valve is 1.15 rather than 1.51
D O'Neill

This is off my MKI project car engine (948). I'm rebuilding the engine to factory specs so I'm not using this head. The engine ran before it was disassembled a few years ago. I have not had it checked for cracks yet. I'm taking it to have it checked Monday.
Jon Saylor

This thread was discussed between 10/11/2011 and 12/11/2011

MG Midget and Sprite Technical index

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