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Cooper S heads
https://www.ausmini.com/forums/viewtopic.php?f=2&t=7710		 Page 1 of 2
Author:  tsgwon [ Tue May 31, 2005 8:44 pm ]
Post subject:  Cooper S heads
Is anyone out there prepared to have a crack at expounding on the different (?) heads fitted to Australian Cooper S's. 12A185, 12G940, big valve, small valve, blah, blah, blah... Was there only ever one type, or did it change somewhere along the line?

There's a lot of info out there (books, web, rumour, innuenndo) but much of it is conflicting... :roll:

Cheers,

Jamie
Author:  unit [ Tue May 31, 2005 9:02 pm ]
Post subject: 
Mate i definately am not an expert but i am told that there is a difference
the head in my mk 2 s is a mk1. i am told its better. This may just be bull but
ill have to ask my dad why they changed it in the first place(it was 20 yrs ago).
unit
Author:  drmini in aust [ Tue May 31, 2005 9:09 pm ]
Post subject: 
AFAIK, early Oz 1275 S all came with the AEG163 head. They had 1.401" inlets and 1.219" exhausts. Sometime later, around 1967-8-9?? they went to the 12G1805 head, which is a 12G940 casting with 1.401" inlets and 1.156" exhausts. Both these heads had 11 stud holes.
Originals 12G940 S ones were usually stamped 12G1805 near the thermostat housing.

A Morris 1100S head is very similar, effectively it's the same 12G940 casting but with 1.312" inlet valves. Some (not all) were stamped 12G938 near the thermostat housing.
It's easy to convert these to the S size valves & extra stud holes, I just did one for 1310/71. :wink:
Author:  drmini in aust [ Tue May 31, 2005 9:11 pm ]
Post subject: 
I've been told these days you can get better flow figures from a 12G940 casting than the early MK1 types. The port shapes above the seats are better.
BTW the valves are longer on the 940, DO NOT put MK1 valves in a 940 head, you will get valve spring crush with any decent cam lift.
Author:  unit [ Tue May 31, 2005 9:14 pm ]
Post subject: 
So Dr mini is that why maybe they changed our head to an earlier one?
The fact that the exhaust valves are bigger?
unit
Author:  unit [ Tue May 31, 2005 9:15 pm ]
Post subject: 
sorry you answered my question before i posted it.
unit
Author:  drmini in aust [ Tue May 31, 2005 9:16 pm ]
Post subject: 
unit wrote:
So Dr mini is that why maybe they changed our head to an earlier one?
The fact that the exhaust valves are bigger?
unit

Could be. But you can get the same size bigger exhaust valves now for the MK2 heads, I've got race ones in mine.. 8)
means I can't fit unleaded seats though. :lol:
Author:  unit [ Tue May 31, 2005 9:21 pm ]
Post subject: 
well i guess it doesnt matter anyway.
The heads have unleaded set up fitted now so i guess it all worked out ok.
JUst need the bloody clutch fixed(hopefully this week).
unit
Author:  Lillee [ Tue May 31, 2005 11:51 pm ]
Post subject: 
Then it gets complicated from here as there were more than 1 type of 12G940 castings. The later metro 12G940 heads had the bigger inlet and exhaust valves just the same as the big vavle Cooper ones did but had different valve train...
Author:  drmini in aust [ Wed Jun 01, 2005 7:26 am ]
Post subject: 
68Delux wrote:
Then it gets complicated from here as there were more than 1 type of 12G940 castings. The later metro 12G940 heads had the bigger inlet and exhaust valves just the same as the big vavle Cooper ones did but had different valve train...

Yeah for some reason all the Metro heads are called 12G940.
Common Metro had 1100S size inlets.
The MG Metro had the S sized 1.401" inlets.
All of them had the 1.156" exhaust valves, not the 1.219" of the MK1 S.
These heads are supposed to need less work to make them go than the early ones. But comparing Chong's MG Metro one to Makka's MK2 S, I can't see much difference.

You don't really need 1.219" exhausts, GR's race heads have the 1.156" exhausts. And he's getting over 150HP from them now. :P
As on Greig Malaure's one.
Author:  miniron [ Wed Jun 01, 2005 9:34 am ]
Post subject: 
8)

OZ built Mk1 cars used the AEG163 head with the thin flange block and 9FSAY engine numbers. Built up to the end of 68 including MK1.5 cars.
AEG163 heads were painted blue on the top under the rocker gear. Earlier heads were painted yellow and had some overheating problems but I don't think any of these were on OZ built cars. Most likely on UK built 1071 cars etc.
MK2 cars used the 12G940 casting with 12G1805 stamped next to the thermostat housing. These cars had the thick flange block and 9FXEY engine numbers.
Clubman GT cars also used this head block combo but the engine number prefix was changed to 1200 supposedly to rationalise the engine number codes. I think all it did was introduce another list of different prefixes to confuse us mere mortals not part of the BMC/Leyland inner sanctum. The last Clubman GTs are supposed to have used non S blocks with big journal cranks but presumeably still used the 12G1805 marked head.
There are some differing views about which cars had which blocks, heads etc during the changeover from MK1 to MK2 cars.
MK2 production didn't start until approx May 69, or at least no MK2 cars were available for sale until May 69. Were there any MK1.5 cars built in the first part of 69? Who knows.
My own MK1.5 car was built in the last part of 68 and is one of the last ones built. Car number is in the 4800 range. My own personal opinion, not necessarily correct, is that there were no MK1/1.5 cars built in 69. Others may have differing views.
Valve sizes, lengths etc are as DRMINI has said above.
Don't know about the later Metro heads except I remember reading somewhere that the Metro head 12G940 casting had the inlet valve throat shape changed to provide a sort of venturi effect to increase gas flow into the engine. Something to do with emissions, fuel consumption etc. The AEG163 head is a little bit like this too compared to the 12G940 head.

Hope this helps
Regards
RonR
Author:  drmini in aust [ Wed Jun 01, 2005 7:24 pm ]
Post subject: 
Ron,
I just stripped Chong's stocko MG Metro head- the inlet valves are S sized, but the whole thing needs blending in. They have just opened the throats with a 60* cutter to suit the bigger valves, and the step at the corner is worse than any 12G1805 (MK2 S) head.... :x
Nothing my trusty die grinder won't fix though... 8)
Author:  Lillee [ Thu Jun 02, 2005 9:45 am ]
Post subject: 
Shhh don't give too many secrets away Kev! :wink:
Author:  FIGJAM [ Thu Jun 02, 2005 5:57 pm ]
Post subject: 
Hi all.
Can someome tell me what the 12G941 head is ? Is that genuine Cooper?
That previous info is pretty handy. :wink:
Cheers
Author:  gafmo [ Thu Jun 02, 2005 6:22 pm ]
Post subject: 
Try this site for Head Details
http://drcwww.kub.nl/~bogaard/heads.htm
Sorry 12g941 does not come up but here is some more info :?
http://www.minis.com.au/wholesale%20cat ... d%20p3.htm
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