Cylinder head - 970, 1071 and 1275cc (cooper s)

970, 1071 and 1275cc Cooper S Cylinder Head Identification
Cylinder head details in this section are appropriate for all variants of Cooper S engine, built between 1963 and 1971. Three cylinder head designs were used,
identifiable by casting numbers 12A185, AEG163 and 12G940. All three will fit any capacity Cooper S engine and all three are interchangeable as complete
assemblies. This does not, however, mean that all components can be easily swapped between them.

All Cooper S cylinder heads are referred to as 'eleven stud' heads because of the attachment method to the cylinder block (actually inaccurate since ten studs and
a bolt are used); all other Mini cylinder heads are attached with nine studs. The two extra fixings are clearly visible at either end of the rocker cover, the gasket flange
of which is notched to accept them. The only other BMC/Leyland engine to be fitted with an eleven stud cylinder head was that to be found in the high performance
derivatives of the Austin/Morris 1300 (1300 GT, MG 1300 etc.) and the Italian-built Innocenti Mini Cooper 1300, and indeed the cylinder head fitted was the 1969-71
Cooper S item. This does not mean however that the 1300 GT engine is a Cooper S engine, since there are many other differences between them, including the
engine block itself, but it still makes a very desirable power unit to transplant into a Mini.

The first Cooper S cylinder head, introduced on the 1071cc model in 1963, was marked with the casting number 12A185 and additionally may be identified by
a yellow colour coding. The valves fitted are distinctly larger than those in the cylinder heads of non-Cooper S Minis - the inlet valve is 1 13/32" (35.6mm) in
diameter and the exhaust valve is 1 7/32" (31mm) in diameter. Additionally, the valves are uniquely manufactured in Nimonic 80 (EN214N) steel and use double
valve springs.

Towards the end of 1963 a new cylinder head casting was introduced, marked with the part number AEG163 and colour coded blue or brown. The only difference
between the 12A185 and AEG163 castings is a production modification in the internal oil ways in the later casting; it affects neither performance nor reliability of
the head. The valves, valve springs and rocker gear all continued unchanged from the 12A185 head. The AEG163 cylinder head was fitted from late 1963 through
to 1969 and thus saw use on the last 1071cc engines, all 970cc engines and all but the last 15 months or so of 1275cc engine production.

The 12G940 cylinder head casting was officially introduced on the 1275cc Cooper S engine at the beginning of Mini Mk III production, for the 1970 model year.
Alongside the casting number in the centre of the top face of the head, the other identifying mark is the part number 12G1805 stamped by the thermostat housing.
It may well also have been fitted to the last few Cooper S Mk IIs; this is difficult to prove, not least because the factory parts and service department soon
offered the 12G940 head as the only replacement for all Cooper S heads, meaning that a significant number of 1960s cars are now fitted with them. Using the
eleven stud 12G940 head on the Cooper S saved manufacturing costs through component sharing with other models (the aforementioned Austin/Morris 1300 and
Innocenti).

It also improved Cooper S cylinder head reliability, for a small cost in performance, since smaller exhaust valves in the 12G940 head allowed for more material to
be left between the inlet and exhaust valves; this area was prone to cracking on the 12A185 and AEG163 heads. The inlet valve size on the 12G940 is, as
previously, 1 13/32" (35.6mm) diameter, but the exhaust valve size is reduced by 1/16" to 1 5/32"(29.4mm) diameter. The valves are made from standard, not
Nimonic, material and have longer stems to compensate for the higher valve spring seat on the 12G940 casting. Thus even the inlet valves are not directly
interchangeable with earlier Cooper S items, though their diameter is the same.

The nine stud fixing 12G940 cylinder heads used on other 1275cc BMC/Leyland/Austin Rover engines are not, of course, capable of being fitted to a Cooper S
engine without very costly modification - they usually have smaller valves than the eleven stud 12G940 (MG Metro etc. excepted) anyway.

At various times during A Series engine production, new and reconditioned cylinder heads from the factory were either in 'assembly' or 'bare' condition.
Assemblies usually included studs, valves, valve springs and guides (but not rockers, rocker shaft and pedestals) whereas bare heads included valve guides
and studs or valve guides only. These states of build were however not hard and fast, so if you are offered a new or reconditioned factory cylinder head on an
exchange unit scheme you should establish before ordering exactly what you will receive, to guard against the possibility of giving away components on your old
head that you will still need in future!

Rebuilt or Repaired 970, 1071 and 1275cc Cylinder Heads
Somerford Mini Ltd. offers a bespoke cylinder head rebuilding and repair service. In our experience, a large number of customers require some degree of modification
to their cylinder heads and as a result, whether you want a standard head or one that is uprated to any degree, we ask you to contact us to discuss your requirements.
It would be helpful if you could also supply us with the details of your engine: full engine number (if known) and type (capacity, high or low compression, gearbox,
breathing system, etc.), plus any existing modifications. The more you can provide us with, the better we can help you. All of our cylinder heads are built to
run on lead-free fuel, unless you specify otherwise.
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
1	-	CYLINDER HEAD ASS'Y, with valves	1	970, 1071 and 1275cc 1963-69.
		(12A185 or AEG163 casting)
	-	CYLINDER HEAD ASS'Y, with valves	1	1275cc 1969-71.
		(12G940 casting)
2	-	CYLINDER HEAD, bare, with guides and studs only	1	970, 1071 and 1275cc 1963-69.
		(12A185 or AEG163 casting)
	-	CYLINDER HEAD, bare, with guides and studs only	1	1275cc 1969-71.
		(12G940 casting)

Gasket Set
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
3	GEG103SMC	GASKET SET, cylinder head	1
The cylinder head gasket set, also known as a 'decoke' or 'decarbonising' set, includes the cylinder head gasket, manifold gasket, two thermostat housing
gaskets (one extra to cater for other 1275cc Mini engines with sandwich plates), HS2, HS4 and HIF carburetter gaskets, rocker cover gasket, plus heater take-off
gasket. The rocker cover gasket will require two small notches to be cut in it to allow for the extra Cooper S cylinder head fixings. Valve stem oil seals are not
included in the set, leaving customers to choose the type and quantity they need and order them separately.

Cylinder Head Components
Cylinder Head Fixings
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
4	GEG300	GASKET, cylinder head, copper	1
5	CAM150	STUD, cylinder head, long	4
6	CAM151	STUD, cylinder head, short	6
7	51K1193	NUT, cylinder head to block	10
8	PWZ106	WASHER, plain	10
	GB126B	WASHER, plain	9	Alternative heavy duty washer. Withstands up to 80lbf ft torque.
9	AEG248	BOLT, cylinder head	1
10	PWZ106	WASHER, plain	1

Plugs and Adaptors
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
11	2K1345	PLUG, oil hole, cylinder head	1	Alternative to 6K808.
	6K808	PLUG, oil hole, cylinder head	1	Alternative to 2K1345.
12	12G2092	PLUG, water hole	3
13	AEA771	PLUG, water and dowel hole	2
14	12G3503	PLUG, cleaning hole	3/2	Qty. decreases for 12G940 head.
15A	2A243	ADAPTOR, by-pass hose, short	1
15B	CAM4126	PLUG, bypass adaptor blanking	A/R	Use if thermostat blanking sleeve is fitted.
15C	3H2963	CLIP, bypass blanking plug	A/R

Thermostat Housing and Fixings
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
16	-	HOUSING, thermostat	1
For details of thermostat housings, please see the 'Cooling - Thermostats and Water Pumps' section in the Cooling and Heating area of the Somerford Mini catalogue.

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
17	GTG101	GASKET, thermostat housing, cork	1
	GUG705558	GASKET, thermostat housing, paper	1
In theory the two gasket materials are interchangeable, but the cork gasket seems to be preferred by Somerford Mini customers for a simple thermostat housing fitment, whereas the later paper gasket is preferred for a thermostat housing with sandwich plate (not applicable for Cooper S engines).

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
18	CHS2515	STUD, thermostat housing	3
19	FNZ105	NUT	3
20	PWZ105	WASHER, plain	3

Heater Valve and Fixings
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
21	-	VALVE, heater	1	See note below.
For details of the heater valves, please see the 'Heating - Heater Hoses, Water Control Valves and Cables' section in the Cooling area of the Somerford Mini catalogue.

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
22	2A180	PLATE, blanking heater take-off in cylinder head	1	For models without heater.
23	88G221B	GASKET, heater valve	1
24	53K402	STUD, heater valve	2
25	FNZ104	NUT	2
26	LWZ304	WASHER, locking	2

Manifold Fixings
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
27	GUG704053MG	GASKET, manifold, standard	1
28	53K487	STUD, manifolds	6
29	12A1211	WASHER, plain, large, clamping manifolds	4
30	PWZ105	WASHER, plain	2
31	GHF261	NUT, brass, manifolds to cylinder head	6
	51K1177	NUT, brass, manifolds to cylinder head, long	6	Alternative; easier to access.

Rocker Cover and Fixings
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
32	AEG172	ROCKER COVER, steel, with breather pipe	1	1963-64 open circuit breathing models.
33	AEG512	ROCKER COVER, steel, without breather pipe	1	1964-71 closed circuit breathing models.
34	CAM6822	ROCKER COVER, alloy, without breather pipe	1	Accessory (also MG Metro) item for closed circuit breathing models.
A range of polished or painted alloy accessory rocker covers is available from Somerford Mini; please contact us for details. Note that some accessory rocker covers require different fixings from the standard items.

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
35	-	PLATE, engine name	1	See note below.
	-	DECAL, engine name	1	See note below.
	-	PLATE, engine patent	1	See note below.
	-	DECAL, engine patent	1	See note below.
For details of the large range of plates and decals fixed to rocker covers, please see the 'Chassis Plates and Decals' section in the Interior Body Fittings area of the Somerford Mini catalogue.

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
36	12A402	CAP, oil filler, black plastic, without breather	1	1963-64 open circuit breathing models.
37	13H2296	CAP, oil filler, black plastic, with breather	1	1964-71 closed circuit breathing models.
38	GFE6007	CAP, oil filler, red plastic, with breather	1	For CAM6822 alloy rocker cover.
39	12A403	SEAL, plastic oil filler cap	1	For 12A402 and 13H2296 caps.
40	GEG417	GASKET, rocker cover, original	1	With notches to clear cylinder head fixings.
	GEG401	GASKET, rocker cover, replacement	1	Notch before fitting.
41	CAM6822FK	CHROME FIXINGS KIT, rocker cover	1
Includes chrome nuts, chrome distance pieces, chrome cup washers and rubber bushes. For alloy rocker covers such as CAM6822.

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
42	2A150	NUT, rocker cover to engine	2	Original zinc finish.
	2A150C	NUT, rocker cover to engine	2	Chrome, for steel rocker covers.
	CAM6823	NUT, rocker cover to engine	2	Chrome, longer, for alloy rocker covers.
43	1B2925	DISTANCE PIECE	2	Original zinc finish.
	12G687	DISTANCE PIECE	2	Alternative chrome finish.
44	1A2156	WASHER, cup	2	Original zinc finish.
	12G679	WASHER, cup	2	Alternative chrome finish.
45	12A1358	BUSH, rubber	2
46	12A1968	LIFTING EYE, engine, temporary fitment	2	Fit to engine only while lifting work is taking place.

Rocker Shaft, Rockers and Fixings
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
47	12G1926	PEDESTAL, rocker shaft, with oil hole	3
48	12G1927	PEDESTAL, rocker shaft, with tapped hole	1
49	2A258	SCREW, locating rocker shaft	1
50	2A515	PLATE, securing screw	1	Original item.
51	2A259	PLATE, securing screw	1	Replacement item.
52	51K885	STUD, long, rocker cover and rocker pedestal	2	Outer pedestals.
53	CHS522	STUD, short, rocker pedestal	2	Inner pedestals.
54	LNZ205	NUT, nyloc, pedestal to cylinder head	4
55	PWZ105	WASHER, plain	3	Not used on tapped pedestal.
56	PWZ106	WASHER, plain	3	Not used on tapped pedestal.
57	AEG399	ROCKER SHAFT ASS'Y	1	Original item.
58	12A1950	ROCKER SHAFT	1	Replacement item.
59	6K878	END PLUG, plain	1	Included in AEG399 rocker shaft ass'y.
60	2K4608	END PLUG, screwed	1	Included in AEG399 rocker shaft ass'y.
61	12G1221	ROCKER, forged	8	Original item.
62	CAM289	ROCKER, scintered	8	Replacement item.
Only forged rockers were fitted to Cooper S engines when built. However, after the introduction of the scintered rocker on other A Series engines in 1974, either
forged or scintered rockers were offered as replacement parts. The forged rocker is acknowledged as the stronger of the two and is of course correct for originality.
However for normal road use it does not matter which type of rocker is used, so long as (i) all eight on the rocker shaft are of the same type; (ii) all eight are either
the same age from the same engine or are new; and (iii) the tappet adjusting screws and nuts, plus the rocker spacing washers, are correct for the type of rocker.
Note that the forged rockers have replaceable bushes, whereas scintered rockers do not.

Several designs of high-lift and roller rockers are also available for tuning purposes, along with special valve springs to avoid coil binding, if necessary. Please contact Somerford Mini for details of these and other engine tuning parts.

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
63	2A21	BUSH, rocker	8	Included in forged rocker.
64	5C2436	RIVET, bush to rocker	8	Included in forged rocker.
65	AEG167	SCREW, tappet adjusting	8	Use with forged rocker.
66	NT605061	NUT, locking screw	8	Use with forged rocker.
67	12H3376	SCREW, tappet adjusting	8	Use with scintered rocker.
68	51K1178	NUT, locking screw	8	Use with scintered rocker.
69	6K556	SPRING, rocker spacing	3
70	AEG168	DISTANCE PIECE, exhaust rocker	6	For forged rockers.
71	2A18	WASHER, double coil, outer ends of shaft	2	For scintered rockers.
The distance piece AEG168 is used to shim forged rockers on their shaft correctly over the exhaust valves. It is only required on big bore (970, 1071 and 1275cc)
cylinder heads, where the valves are spaced further apart than is the case on other A Series engines. The wider scintered rockers do not require these shims, so
instead revert to the more usual A Series set up of using double coil (or 'Thackery') washers at either end of the rocker shaft.

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
72	6K555	WASHER, plain, outer ends of shaft	2
73	ZPS314	SPLIT PIN, outer ends of shaft	2

Valve Guides and Valve Seat Inserts
Originally on the 12A185 and AEG163 cylinder heads the valve guides were different for inlet and exhaust valves. The 12G940 head had a single valve guide
design, and this is now offered for all Cooper S cylinder head applications. This valve guide, 12G1963, will accept the later 'top hat' type valve stem oil seal
(ADU4905) if required.
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
74	12G1963	GUIDE, inlet and exhaust valve	8
75	12G1089	INSERT, inlet valve seat	4	Not lead free fuel compatible.
76	12G2675	INSERT, exhaust valve seat	4	For 12A185 and AEG163 heads. Pete - is this lead free?
	TAM2069	INSERT, exhaust valve seat	4	For 12G940 heads; lead free fuel compatible.

Valves and Valve Springs
As stated in the introduction to this section, the valve stem lengths are particular to the cylinder head castings found on Cooper S models, as are exhaust valve
diameters. The age of the car provides no guarantee as to which cylinder head will be present. Please check your casting number and valve sizes before ordering
replacements from Somerford Mini. A range of uprated valves, valve springs and caps to suit most uses are also available from Somerford Mini; please contact us
for details.

12A185 and AEG163 Cylinder Head Castings
(originally 1963-69 models)
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
77	AEG593	VALVE, inlet, 1 13/32" (35.6mm) dia.	4	Nimonic 80 (EN214N) material.
78	AEG594	VALVE, exhaust, 1 7/32" (31mm) dia.	4	Nimonic 80 (EN214N) material.
79	C-AEA525	SPRING SET, valves, outer and inner	1
80	AEA767	SPRING, valve, outer	8	Included in spring set.
81	12G1137	SPRING, valve, inner	8	Included in spring set.
82	88G459	SPLIT COLLET, pair, valve retaining	8
83	AEA653	CAP, upper, valve springs, steel	8
84	AEA403	COLLAR, lower, valve springs	8
85	AEG327	OIL SEAL, valve stem	8

12G940 Cylinder Head Castings
(originally 1969-71 models)
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
86	AEG592	VALVE, inlet, 1 13/32" (35.6mm) dia.	4
87	12G1322	VALVE, exhaust, 1 5/32" (29.4mm) dia.	4
	CAM4601	VALVE, exhaust, 1 5/32" (29.4mm) dia.	4	Alternative.
88	C-AEA525	SPRING SET, valves, outer and inner	1
89	AEA767	SPRING, valve, outer	8	Included in spring set.
90	12G1137	SPRING, valve, inner	8	Included in spring set.
91	88G459	SPLIT COLLET, pair, valve retaining	8
92	88G617	CAP, upper, valve springs	8	Original item.
	AEA653	CAP, upper, valve springs, steel	8	Uprated alternative.
93	AEA403	COLLAR, lower, valve springs	8
94	AEG327	OIL SEAL, valve stem	4
Oil seals were usually fitted on the inlet valve stems only, but they can be fitted on exhaust valves too. Opinions differ on which is better - the choice is yours.

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Cylinder head - 970, 1071 and 1275cc (cooper s)

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