Cylinder head - 1275cc (not cooper s)

1275cc Cylinder Head Identification
Cylinder head details in this section are appropriate for the 1275cc engine used in Mini 1275 GTs between 1969 and 1980, the 'high performance' Mini Cooper
from 1990 onwards and 'standard performance' Minis from 1992 onwards. The 'eleven stud' cylinder heads for 1275cc Mini Cooper S engines, built up to 1971, are
described in the next section of the Somerford Mini catalogue.

The cylinder head design for the non-Cooper S 1275cc Mini engine was shared with many other BMC/Leyland/Austin Rover model engines, but unlike other A
Series cylinder heads it was only ever fitted to the one size of engine. Thus other cars sharing the cylinder head were all 1275cc models, including the Austin/
Morris 1300 (but not the high performance versions, which used the late Cooper S head), Morris Marina and Ital 1.3, Austin Allegro 1300 and 1.3, Austin Healey
Sprite Mk IV/MG Midget Mk III, Austin/MG Metro, Austin Maestro and Montego. The number cast into the cylinder head is 12G940, but note that there are several
versions of cylinder head identified by this number, which means that care has to be taken when sourcing a head to use on your Mini.

Different versions of 12G940 heads used either 1 5/16" (33mm) or 1 13/32" (35.6mm) inlet valves; 1 5/16" is the correct diameter for an inlet valve in an original
non-Cooper S Mini engine (exhaust valves are always 1 5/32" (29.4mm) diameter, whatever the application). Cooper S, high performance Austin/Morris 1300 and
MG Metro models somehow squeezed in the larger 1 13/32" diameter inlet valves. Confusingly, the last Cooper S cylinder heads plus the aforementioned high
performance 1300 heads are still 12G940 castings, even though they have 'eleven stud' fixings to the cylinder block (standard 12G940s are nine stud); they do
however have an extra 12G1805 part number stamped by the thermostat housing for additional identification. As mentioned at the beginning, these later Cooper
S heads are dealt with in the next section.

Late model 12G940 castings, used on 1990s Minis, can be distinguished by separate sculpted and machined areas around the thermostat housing and heater
take off, whereas the earlier castings are machined straight across from these areas to the rocker cover. Once again, care needs to be taken here: do not
assume that if you have identified a late casting it must be Mini specification. Metros also used this casting with the heater take-off blanked off (as was the
take-off on fuel injection and 1992-94 carburetter Mini heads), and the MGs had the larger 1 13/32" inlet valves. Metro Turbos and ERA Mini Turbos similarly used
late type 12G940 heads, this time with Mini sized inlet valves - the valves are however sodium filled and the deck of the cylinder head is thinner.

Lastly, mention should be made of the air injection cylinder head used on North American specification (NAS) Austin Healey Sprite Mk IVs, MG Midget Mk IIIs
and Austin Americas between 1968 and 1974. This head casting, displaying part number 12G939, is a strengthened version of the 12G940 including air injection
ports for the NAS emission control systems. While on the face of it not strictly relevant to a Mini parts catalogue, it is in all other respects a 12G940 head
and because of its increased strength it makes an ideal and reliable candidate for tuning treatment. Plenty of new 12G939 heads were still around in the
classic car parts marketplace at the beginning of the 1990s and while it will not be easy, you can find one even now if you want one.

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 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	1275 GT 1969-80; please contact us for details.
		(early 12G940 casting)
	-	CYLINDER HEAD ASS'Y, with valves	1	Cooper carburetter 1990-91; please contact us for details.
		(late 12G940 casting)
	-	CYLINDER HEAD ASS'Y, with valves	1	Single point injection 1991-96; please contact us for details.
		(late 12G940 casting)
	-	CYLINDER HEAD ASS'Y, with valves	1	1275cc carburetter 1992-94; please contact us for details.
		(late 12G940 casting)
	-	CYLINDER HEAD ASS'Y, with valves	1	Multi and single point injection 1997 on; please contact us for details.
		(late 12G940 casting)
2	-	CYLINDER HEAD, bare, with guides and studs only	1	1275 GT 1969-80; please contact us for details.
		(early 12G940 casting)
	-	CYLINDER HEAD, bare, with guides only	1	Cooper carburetter 1990-91; please contact us for details.
		(late 12G940 casting)
	-	CYLINDER HEAD, bare, with guides only	1	Single point injection 1991-96; please contact us for details.
		(late 12G940 casting)
	-	CYLINDER HEAD, bare, with guides only	1	1275cc carburetter 1992-94; please contact us for details.
		(late 12G940 casting)
	-	CYLINDER HEAD, bare, with guides only	1	Multi and single point injection 1997 on; please contact us for details.
		(late 12G940 casting)

Gasket Set
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
3	GEG103SMC	GASKET SET, cylinder head	1	Carburetter models 1969-94; see note below.
	GEG103SMI	GASKET SET, cylinder head	1	Single and multi point injection 1991 on; see note below.
The cylinder head gasket set, also known as a 'decoke' or 'decarbonising' set, includes the cylinder head gasket, manifold gasket (standard in the carburetter type
gasket set, reinforced in the injection type set), two thermostat housing gaskets (one extra to cater for engines with sandwich plates), HS2, HS4 and HIF carburetter
gaskets (carburetter type gasket set only), rocker cover gasket, plus heater take-off gasket (carburetter type gasket set only). Valve stem oil seals are not included,
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	5/4	Qty. reduced 1990-96.
	TAM1617	STUD, cylinder head and coil bracket	1	1990-96.
7	51K1193	NUT, cylinder head to block	9	1969-78 standard fitment.
8	PWZ106	WASHER, plain	9	1969-78 standard fitment.
	GB126B	WASHER, plain	9	Alternative heavy duty washer. Withstands up to 80lbf ft torque.
9	CAM4545	NUT, flanged, cylinder head to block (does not require plain washer)	9	1978 on standard fitment. 1969-78 heavy duty alternative.
	CAM4545	NUT, flanged, coil bracket to cylinder head stud	1	1990-96.

Plugs and Adaptors
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
10	2K1345	PLUG, oil hole, cylinder head	1	1969-80, alternative.
	6K808	PLUG, oil hole, cylinder head	1	1969-80, alternative.
11	CDU2601	RIVET, oil hole, cylinder head	1	1990-96.
	LYQ100050	RIVET, oil hole, cylinder head	1	1997 on.
12	12G2092	PLUG, water hole	3	1969-96.
	154545A	PLUG, water hole	3	1997 on.
13	AEA771	PLUG, water and dowel hole	2
14	12G3503	PLUG, cleaning hole	2	1969-96.
15A	12A2075	ADAPTOR, by-pass hose, long	1	1969-80 and 1275cc carburetter models 1992-94.
15B	CAM4126	PLUG, bypass adaptor blanking	A/R	1990-91, Cooper Rover Special Products and Cooper Carburetter (if fitted). Also 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	1/2	Qty. 2 required 1990 on.
	GUG705558	GASKET, thermostat housing, paper	1/2	Qty. 2 required 1990 on.
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 (applicable for 1990 on).

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
18	CHS2515	STUD, thermostat housing	3	1969-80 (carburetter models).
	CHS2524	STUD, thermostat housing and sandwich plate	3	1990-91 (carburetter models).
19	FNZ105	NUT	3	1969-91 (carburetter models).
20	PWZ105	WASHER, plain	3	1969-91 (carburetter models).
21	DAM7760	BOLT, thermostat housing and sandwich plate	3	1991 on (injection and 1992-94 carburetter models).

Heater Valve and Fixings
1275 GT 1969-80
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
22	-	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
23	88G221B	GASKET, heater valve	1
24	53K402	STUD, heater valve	2
25	FNZ104	NUT	2
26	LWZ304	WASHER, locking	2

Heated Manifold Adaptor and Fixings
Cooper Carburetter 1990-91
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
27	12G2534	ADAPTOR, heated manifold take-off	1
28	88G221B	GASKET, adaptor to cylinder head	1
29	TAM1368	SCREW, adaptor to cylinder head	2

Combined Inlet and Exhaust Manifold Fixings
1275 GT 1969-80 and 1275cc Carburetter Models 1992-94
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
30	GUG704053MG	GASKET, manifold, standard	1
31	53K487	STUD, manifold	6	1969-80.
	LYR10028	STUD, manifold	6	1992-94.
32	12A1211	WASHER, plain, large, clamping manifold	4
33	PWZ105	WASHER, plain	2
34	GHF261	NUT, brass, manifold to cylinder head	6
	51K1177	NUT, brass, manifold to cylinder head, long	6	Alternative; easier to access.
	FNZ105	NUT, steel	6	Alternative.
The steel nut alternative was fitted off and on over the years (most likely as a panic measure when the production line ran out of brass nuts) but does tend to sieze on the manifold studs unless plenty of copper grease is applied.

Separate Inlet and Exhaust Manifold Fixings
Cooper Carburetter 1990-91
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
35	GUG704053MG	GASKET, manifold, standard	1
36	53K487	STUD, manifold	6
37	PWZ105	WASHER, plain	6
38	GHF261	NUT, brass, manifolds to cylinder head	6

Separate Inlet and Exhaust Manifold Fixings
Injection Models 1991 On
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
39	GUG704063MG	GASKET, manifold, reinforced	1
40	LYR10028	STUD, manifold	6	1991-96 single point injection.
	53K487	STUD, manifold, outer	2	1997 on multi and single point injection.
	LYR10028	STUD, manifold, inner	4	1997 on multi and single point injection.
41	PWZ105	WASHER, plain	2
42	GHF261	NUT, brass, manifolds to cylinder head	2
43	LYH10008	NUT AND WASHER, manifolds to cylinder head	4

Rocker Cover and Fixings
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
44	12A1530	ROCKER COVER, steel, black	1	1969-80.
	LDR10074	ROCKER COVER, steel, black	1	1990 on.
	LDR103490	ROCKER COVER, steel, citrus green	1	1998, Paul Smith limited edition.
45	CAM6822	ROCKER COVER, alloy	1	Accessory (also MG Metro) item.
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
46	-	DECAL, rocker cover	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
47	13H2296	CAP, oil filler, black plastic, with breather	1
48	GFE6007	CAP, oil filler, red plastic, with breather	1	For CAM6822 alloy rocker cover.
49	12A403	SEAL, plastic oil filler cap	1	For 13H2296 cap.
50	GEG401	GASKET, rocker cover	1
51	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
52	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.
53	1B2925	DISTANCE PIECE	2	Original zinc finish.
	12G687	DISTANCE PIECE	2	Alternative chrome finish.
54	1A2156	WASHER, cup	2	Original zinc finish.
	12G679	WASHER, cup	2	Alternative chrome finish.
55	12A1358	BUSH, rubber	2
56	12H2557	NUT, extension, air intake to rocker cover	2	1990-91 carburetter models.
57	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
58	12G1926	PEDESTAL, rocker shaft, with oil hole	3
59	12G1927	PEDESTAL, rocker shaft, with tapped hole	1
60	2A258	SCREW, locating rocker shaft	1
61	2A515	PLATE, securing screw	1	1969-74.
62	2A259	PLATE, securing screw	1	1974 on; will fit 1969-74 models.
63	51K885	STUD, long, rocker cover and rocker pedestal	2	Outer pedestals.
64	CHS522	STUD, short, rocker pedestal	2	Inner pedestals.
65	LNZ205	NUT, nyloc, pedestal to cylinder head	4	1969-80.
66	PWZ105	WASHER, plain (not used on tapped pedestal)	3	1969-80.
67	PWZ106	WASHER, plain (not used on tapped pedestal)	3	1969-80.
68	NH605040	NUT, pedestal to cylinder head	4	1990 on.
69	PWZ105	WASHER, plain (not used on tapped pedestal)	3	1990 on.
70	AEG399	ROCKER SHAFT ASS'Y	1	1969-74.
71	12A1950	ROCKER SHAFT	1	1974 on; will fit 1969-74 models.
72	6K878	END PLUG, plain	1	Included in AEG399 rocker shaft ass'y.
73	2K4608	END PLUG, screwed	1	Included in AEG399 rocker shaft ass'y.
74	12G1313	ROCKER, pressed steel	8	First rocker type.
75	12G1221	ROCKER, forged	8	Second rocker type.
76	CAM289	ROCKER, scintered	8	Third rocker type, 1974 on.
Pressed steel rockers and the stronger forged rockers were used in standard and high performance engines as alternatives both in production and the parts
department until 1974, when the scintered rocker was introduced. The scintered rocker was used in all engine production from that time onwards, although
the pressed steel and forged types continued to be offered as alternative spare parts for earlier cars. 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
the other two designs 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
77	2A21	BUSH, rocker	8	Included in forged rocker.
78	5C2436	RIVET, bush to rocker	8	Included in forged rocker.
79	12A1215	SCREW, tappet adjusting	8	Use with pressed steel rocker.
80	6K654	NUT, locking screw	8	Use with pressed steel rocker.
81	AEG167	SCREW, tappet adjusting	8	Use with forged rocker.
82	NT605061	NUT, locking screw	8	Use with forged rocker.
83	12H3376	SCREW, tappet adjusting	8	Use with scintered rocker.
84	51K1178	NUT, locking screw	8	Use with scintered rocker.
85	6K556	SPRING, rocker spacing	3
86	AEG168	DISTANCE PIECE, exhaust rocker	6	For pressed steel and forged rockers.
87	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
88	6K555	WASHER, plain, outer ends of shaft	2
89	ZPS314	SPLIT PIN, outer ends of shaft	2

Valve Guides and Valve Seat Inserts
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
90	12G1111	GUIDE, inlet and exhaust valve	8	Standard size.
	12G1111010	GUIDE, inlet and exhaust valve	8	0.010" oversize.
91	12G1089	INSERT, inlet valve seat	4	1969-80, not lead free fuel compatible.
92	12G1090	INSERT, exhaust valve seat	4	1969-80, not lead free fuel compatible.
	TAM2069	INSERT, exhaust valve seat	4	1990 on, lead free fuel compatible.

Valves and Valve Springs
Valves are a lot more simple on the Mini 1275cc cylinder head than on other A Series heads. There are only two types, identifiable by the grooves on the valve
stems into which the retaining collets locate. The 1969-80 design of valve has a single collet groove 1/4" deep, whereas the later (lead free) valve design fitted in
the 1990s has a very distinctive triple groove. Care must be taken to ensure that valves, valve caps and collets are matched before attempting reassembly.
The later triple groove valves, caps and collets may be used as replacements on earlier cylinder heads along with TAM2069 exhaust valve seat inserts as a
lead free conversion.

Austin and MG Metro components are also detailed here for the benefit of the many, many Mini owners who have transplanted Metro power units into their cars.

A range of uprated valves, valve springs and caps to suit most uses are also available from Somerford Mini; please contact us for details.

1969-80 (original pre-A Plus Mini engines)
1980-84 (early A Plus Austin and MG Metro engines)
Valves With 1/4" Collet Groove
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
93	12G941	VALVE, inlet, 1 5/16" (33mm) dia.	4	Mini and Austin Metro engines.
	AEG592	VALVE, inlet, 1 13/32" (35.6mm) dia.	4	MG Metro engines.
94	CAM4601	VALVE, exhaust, 1 5/32" (29.4mm) dia.	4
95	12G1015	SPRING, valve	8
96	88G459	SPLIT COLLET, pair, valve retaining	8
97	88G617	CAP, upper, valve spring	8
98	AEG327	OIL SEAL, valve stem	4/8
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.

1990 On (original A Plus Mini engines)
1984-90 (later A Plus Austin and MG Metro engines)
Valves With Triple Collet Groove
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
99	TAM1058	VALVE, inlet, 1 5/16" (33mm) dia.	4	Lead free fuel compatible; Mini and Austin Metro engines.
	TAM1059	VALVE, inlet, 1 13/32" (35.6mm) dia.	4	Lead free fuel compatible; MG Metro engines.
100	TAM1061	VALVE, exhaust, 1 5/32" (29.4mm) dia.	4	Lead free fuel compatible.
101	12G1015	SPRING, valve	8
102	CAM6975	SPLIT COLLET, pair, valve retaining	8
103	AHU1897	CAP, upper, valve spring	8
104	ADU4905	OIL SEAL, valve stem	8

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Cylinder head - 1275cc (not cooper s)

SPLIT PIN-3/32'' x 1 1/2'' LONG

INSERT-EXHAUST VALVE SEAT-1275cc 1990 ON-UNLEADED USE

STUD-CYLINDER HEAD-FRONT-ACCEPTS COIL BRACKET-'90-'96

VALVE-EXHAUST-TRIPLE COLLET GROOVE- 1 5/32'' 1275cc UNLEADED

VALVE-INLET 35.6mm MG METRO

VALVE-INLET-TRIPLE GROOVE COLLET 1 5/16'' 1275cc UNLEADED

USE: 51K1178

NUT-5/16 UNF NATURAL FINISH

STUD-M8-MANIFOLD TO CYLINDER HEAD & DOWNPIPE-'92 ON

RIVET-OIL HOLE-CYLINDER HEAD-'97 ON

NUT AND WASHER-MANIFOLDS TO CYLINDER HEAD-SPI & MPI

ROCKER COVER-CITRUS GREEN-'PAUL SMITH'

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