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MG Midget and Sprite Technical - cylinder head part numbers

Question for any sages out there:- just wondering...was there a "standard" head attached to 12CC engines from the factory??..
Thanks, Dave
David Cox

The standard 1275 head is the 12G940 casting, although there are different variants.

I've stripped a couple of early 12CC engines and they've had castings very similar to the Cooper S AEG163 head, with three round bosses on the top face, like this...

Dave O'Neill 2

This is the more common head...

Dave O'Neill 2

that's very helpful Dave, thanks!
David Cox

Hi David

I have a 12cc engine and that has the round bosses in the head. Its a very early engine with an EN40B crank and thin wall block.
Bob Beaumont

thanks...I am trying to learn more about the 12CC engine in my car...number 1703 ...although apparently this was not the one originally fitted in the factory [no 629] . The archive records seem to suggest that the factory was experiencing build problems at the end of 1966 with the introduction of the new GAN4 cars. The rear axle was also changed before dispatch. Dave
David Cox

hi Dave

My engine is in a Frogeye. I aquired it many many years ago from a written off Midget (I think!) its 1064. I understand these early engines had the stronger crank (like the cooper S ) to counter crank flex and they were more costly to produce. The later 1275's had a stronger block and the crank material chnged to EN16. According to Horler the first 900 12CC designated engines were withdrawn because of the flex problem and replaced as a temporary measure with the stronger crank. This led to delay in the delivery of the cars.
Bob Beaumont

interesting input, Bob...many thanks
David Cox

As followup to Bob, yes they had immediate warranty claims with shot bottom end bearings. AIUI it was also partly down to the hardening process either not being good enough or not done properly. The EN40 crank was a temporary fix while the engineers sorted out a new hardening process / specification, once this came onstream they reverted to the original material.
David Smith

Interesting info thanks for all the input.
Peter Burgess Tuning

mine has a 12G938 stamping near the thermostat housing. I think this was a head that allowed some gas flow work to be done as it had more land between ports, [Peter?] but I may be wrong. I know that the engine passed through the hands of John Sprinzel back in the 60s...could explain the difference. Thanks again...
David Cox

Dave, my '67 Sprite also has the 12G938 stamping. A bit of internet research that I did ages ago agrees with your comment about the additional 'meat' between ports to allow for gas flowing.

As far as I know mine remains untouched. Either that or it was done so badly it made things worse!
C Mee

This thread was discussed between 10/03/2021 and 13/03/2021

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