46 replies to this topic

[A-Cell]

From memory of the early 1970 tuning scene. The stamped number 12G293 is the assembly part no of the cylinder head (fitted with valves and springs) and was originally fitted to the 1275cc Sprite and Midget. The casting is 12G940. These were the preferred castings used for modification by engine tuners, they were drilled for the extra bolt, ports modified, bigger inlet valves, etc etc.
1300GT (ADO16) used the same casting and was machined to take the extra bolt, this application had a different part number. I believe all the early 12g940 castings had more metal, it was only some time later, possibly with the change to A+ that the casting had just enough metal. The myth that ST had the castings modified is just that, a myth.

There was never a 12G293 head casting, the 1300GT/MK3 S's had a 940 casting that was also stamped 12G1040 iirc behind the thermostat housing.
Stop guessing and do a little research..........

Firstly you did not read my post properly, just jumped in to make me wrong, as I seem to remember you did to me and others before who tried to help. What I posted was that the casting number ( found cast into the head under the rocker) is 12G940 and the assembly number (stamped into the flat machined area behind the thermostat location) is the 12G293. This number was stamped in after assembly of the head in East Works Longbridge factory. And I am not guessing, I know from first hand knowledge, not google. I worked there when they were being made. I used the heads on engines I built for rally use.

So the casting from the foundry was 12G940. Once machined and assembled the heads were stamped with numbers
Hence 12G293 Sprite and Midget.

The 12G940 casting was used on the vast majority of 1275cc engines, so is the common denominator here. All these cars had one
ADO16 1300, ADO28 Marina, Sprite, Midget, ADO67 Allegro, Metro and of course Mini including the last of the Cooper S.

The 12G293 head was for the American market cars which required air injection into the cylinders to meet the US emissions regs an that is why it had extra metal that made it a joy to modify. As usual BL made more vehicles than could be sold in the US and they were sold in the UK. A lot of people removed the air pumps and blocked he injection holes, as the pump drained the power .... But that is another story. So one way or another there were lots of 12G293 heads around in the early 70's

[minilee94]

That's what I though your talking about 12g293 im talking about 12g398

Edited by minilee94, 09 January 2013 - 02:13 PM.

[A-Cell]

They where specially cast for modification by the foundry, thicker deck, port walls etc.

Where is your evidence for this then. How did the foundry carry out these changes and how were the castings identified? The only identification is that stamped into the finish machined head after machining. It was the machining which differentiated the heads NOT the casting process.

[A-Cell]

To the OP. The head you are buying should be checked in the same way as any other second hand head you are buying. If possible reserve the right to return it if it has any problems. As these things are now very old. Obvious things like cracks, face not flat, etc. a good clean then thorough inspection. Hope you get a good one.

[minilee94]

Yeah well it will be sent to me as i cant pick it up

[62S]

the 1300GT/MK3 S's had a 940 casting that was also stamped 12G1040 iirc

You don't remember correctly, it was stamped 1805.

The Sprite & Midget A series heads were not drilled for 11 studs from the factory.

Edited by 62S, 09 January 2013 - 08:03 PM.

[minilee94]

Why has this one got 11 studs then ? Been done as an extra

[62S]

Just because it has been drilled for 11 studs now doesn't mean it always had them.

[minilee94]

I know

[62S]

I know it is not the same head but you mentioned it with an erroneous number so I was merely pointing out your error.

[A-Cell]

To minilee94, the head you are buying, like I advised before, needs careful inspection. 62S is right the 12G938 cylinder head Assembly as used on Sprite and Midget was not drilled for the extra bolt when made in the facory, this will have been added later in its life. When we used to modify them we also drilled them for the extra bolt, so this was probably when it was done. These heads were great for tuning work. No doubt some of them will have been done really well and some, well let's say not so good. Hence why you need to check it carefully.
Of course you will be matching it to your engine (as mr Dilligaf advised) to get the CR right, etc. Once again hope this one is a good one and you enjoy your new engine.

As a matter of interest the other head we used to get hold of to modify was the so called 1300 performance head as fitted to the last of the Cooper S and the 1300GT (ADO16), this had the drilling for the bolt done as standard in the factory. I cannot remember the factory part number but Somerford Mini identifies it as 12G1805. In fact there is a lot of useful information on their site that supports what 62S and I have been saying. it is in their Engine parts list Section 11, Cylinder Head - 1275 (not Cooper S)
http://www.somerford...age=page&id=117

[minilee94]

A cell what stuff should i look out for on it picking it up monday

[mk3 Cooper S]

That was originally a Sprite Midget head

Check for cracks, warping over skimming .
Has it been converted to unleaded?

[A-Cell]

Standard production Sprite and Midget 1275 A 1967 on. With 9 stud holes.

[minilee94]

Okay how tell tell warping and over skimming and dont matter boy unleaded etc being rebuilt and will have it converted