Cylinder head - 998 and 1098cc

998 and 1098cc Cylinder Head Identification
Cylinder head details in this section are appropriate for the 998cc engine used in Minis between 1963 and 1992 (including Riley Elf, Wolseley Hornet and Cooper
models) and the 1098cc engine used in Minis between 1975 and 1981.

The cylinder head design for the standard tune 998cc Mini engine was shared with the 848cc engine, but not the 998cc Cooper unit. It was also shared with
other BMC model engines, including 803 and 948cc units to be found in Morris Minors, Austin A30, A35 and A40 models and the 'Frogeye' Austin Healey Sprite
Mk I. Only the castings marked 2A628 (usually earlier A Series), 12A1456 (later A Series), CAM4005 (air injection type) and CAM4180 (A Plus, 1981 on) are
appropriate for the standard tune 998cc Mini - the outwardly similar 2A629 is not. The other obvious distinguishing feature of this cylinder head is the inlet valve
diameter, which at just 1 1/16" (27mm) is the smallest of any A Series head design.

The 998cc Cooper cylinder head was also fitted to high performance 1098cc engines, including the MG, Wolseley, Riley Kestrel and Vanden Plas Princess
1100 models, plus 1098cc Austin Healey Sprites and MG Midgets. For identification purposes the casting number is 12G206 (only on the earliest produced heads)
or 12G295 (on the vast majority), while inlet valves are 5/32" larger than on the standard 998cc head at 1 7/32" (31mm) diameter. As far as flow characteristics are
concerned, the number 12G295 is writ large in Mini tuners' folklore. It is wholeheartedly recommended for uprated small bore A Series engines for any application
other than full race.

The Mini 1098cc cylinder head design also saw use on several other engines including the single carburetter Austin/Morris 1100, the 948cc Austin Healey Sprite
Mk II and MG Midget Mk I and the earliest incarnation of the Mini Cooper, the 997cc model. For identification purposes the casting number is 12G202 and inlet
valves are 1 5/32" (29.4mm) diameter.

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 usually included valve guides
and studs 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 998 and 1098cc 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	998cc 1963-80 (not Cooper); please contact us for details.
		(2A628 or 12A1456 casting number)
	-	CYLINDER HEAD ASS'Y, with valves	1	998cc 1975-80 (Canada and Sweden); please contact us for details.
		(12A1456 or CAM4005 casting, with air ports)
	-	CYLINDER HEAD ASS'Y, with valves	1	998cc 1981 on (A Plus); please contact us for details.
		(CAM4180 casting number)
	-	CYLINDER HEAD ASS'Y, with valves	1	998cc (Cooper); please contact us for details.
		(12G206 or 12G295 casting number)
	-	CYLINDER HEAD ASS'Y, with valves	1	1098cc; please contact us for details.
		(12G202 casting number)
2	-	CYLINDER HEAD, bare, with guides and studs only	1	998cc 1963-80 (not Cooper); please contact us for details.
		(2A628 or 12A1456 casting number)
	-	CYLINDER HEAD, bare, with guides and studs only	1	998cc 1975-80 (Canada and Sweden); please contact us for details.
		(12A1456 or CAM4005 casting, with air ports)
	-	CYLINDER HEAD, bare, with guides and studs only	1	998cc 1981 on (A Plus); please contact us for details.
		(CAM4180 casting number)
	-	CYLINDER HEAD, bare, with guides and studs only	1	998cc (Cooper); please contact us for details.
		(12G206 or 12G295 casting number)
	-	CYLINDER HEAD, bare, with guides and studs only	1	1098cc; please contact us for details.
		(12G202 casting number)

Gasket Set
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
3	GEG101SM	GASKET SET, cylinder head	1	See note below.
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 later engines with sandwich plates), six HS2 carburetter gaskets, three HS4 carburetter gaskets, rocker cover gasket and heater valve gasket.
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	GUG2506C	GASKET, cylinder head, copper	1
5	CAM150	STUD, cylinder head, long	4
6	CAM151	STUD, cylinder head, short	5
7	51K1193	NUT, cylinder head to block	9	1963-78 standard fitment.
8	PWZ106	WASHER, plain	9	1963-78 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. 1963-78 heavy duty alternative.

Plugs and Adaptors
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
10	2K1345	PLUG, oil hole, cylinder head	1	1963-85; alternative to 6K808.
	6K808	PLUG, oil hole, cylinder head	1	1963-85; alternative to 2K1345.
	RU612123	RIVET, oil hole, cylinder head	1	1985 on.
11A	2A243	ADAPTOR, by-pass hose, short	1	1963-69; use with long by-pass hose.
	12A2075	ADAPTOR, by-pass hose, long	1	1969 on; use with short by-pass hose.
11B	CAM4126	PLUG, bypass adaptor blanking	A/R	Use if thermostat blanking sleeve is fitted.
11C	3H2963	CLIP, bypass blanking plug	A/R
12	12G1454	TUBE, air injection port	4	Canada and Sweden 1975-80.
13	ADP210	PLUG, temperature sender unit boss	1	Models without temperature gauge.
14	1B3664	WASHER, sealing	1	Models without temperature gauge.

Thermostat Housing and Fixings
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
15	-	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
16	GTG101	GASKET, thermostat housing, cork	1/2	Qty. 2 required for Japan 1980 on.
	GUG705558	GASKET, thermostat housing, paper	1/2	Qty. 2 required for Japan 1980 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 Japan 1980 on).

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
17	CHS2515	STUD, thermostat housing	3
	FHS2518	STUD, thermostat housing	3	Canada and Sweden 1975-80.
	CHS2524	STUD, thermostat housing and sandwich plate	3	Japan 1980 on.
18	FNZ105	NUT	3
19	PWZ105	WASHER, plain	3

Heater Valve or Tap and Fixings 1963-88
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
20	-	VALVE, heater	1	See note below.
21	-	TAP, heater	1	See note below.
For details of the heater valves and taps, 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 take-off	1
24	53K402	STUD, heater take-off	2
25	FNZ104	NUT	2
26	LWZ304	WASHER, locking	2

Heater Adaptor and Fixings 1988 On
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
27	12G2534	ADAPTOR, heater, cylinder head	1
28	88G221B	GASKET, adaptor to cylinder head	1
29	TAM1368	SCREW, adaptor to cylinder head	2

Manifold Fixings
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
30	GUG704053MG	GASKET, manifold	1
31	53K487	STUD, manifold	6
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.


Rocker Cover and Fixings
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
35	12A475	ROCKER COVER, steel, with breather pipe	1	1963-69 open circuit breathing models.
36	12A1530	ROCKER COVER, steel, without breather pipe	1	1964 on closed circuit breathing models.
	CAM4543	ROCKER COVER, steel, with breather pipe	1	Canada and Sweden 1975-80.
37	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
38	-	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
39	12A402	CAP, oil filler, black plastic, without breather	1	1963-69 open circuit breathing models.
40	13H2296	CAP, oil filler, black plastic, with breather	1	1964 on closed circuit breathing models.
41	GFE6007	CAP, oil filler, red plastic, with breather	1	For CAM6822 alloy rocker cover.
42	12A403	SEAL, plastic oil filler cap	1	For 12A402 and 13H2296 caps.
43	GEG401	GASKET, rocker cover	1
44	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
45	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.
46	1B2925	DISTANCE PIECE	2	Original zinc finish.
	12G687	DISTANCE PIECE	2	Alternative chrome finish.
47	1A2156	WASHER, cup	2	Original zinc finish.
	12G679	WASHER, cup	2	Alternative chrome finish.
48	12A1358	BUSH, rubber	2
49	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
50	12G1926	PEDESTAL, rocker shaft, with oil hole	3
51	12G1927	PEDESTAL, rocker shaft, with tapped hole	1
52	2A258	SCREW, locating rocker shaft	1
53	2A515	PLATE, securing screw	1	1963-74.
54	2A259	PLATE, securing screw	1	1974 on; will fit 1963-74 models.
55	51K885	STUD, long, rocker cover and rocker pedestal	2	Outer pedestals.
56	51K1473	STUD, short, rocker pedestal	2	998cc, inner pedestals.
	CHS522	STUD, short, rocker pedestal	2	1098cc, inner pedestals.
57	NH605040	NUT, pedestal to cylinder head	4
58	LWZ205	WASHER, locking	4	1963-69.
59	PWZ105	WASHER, plain	3	1969 on. Not used on tapped pedestal.
60	PWZ106	WASHER, plain	3	1969 on. Not used on tapped pedestal.
61	AEG399	ROCKER SHAFT ASS'Y	1	1963-74.
62	12A1950	ROCKER SHAFT	1	1974 on; will fit 1963-74 models.
63	6K878	END PLUG, plain	1	Included in AEG399 rocker shaft ass'y.
64	2K4608	END PLUG, screwed	1	Included in AEG399 rocker shaft ass'y.
65	2A964	ROCKER, pressed steel	8	First rocker type.
66	12G1221	ROCKER, forged	8	Second rocker type.
67	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 are correct for the type of rocker. Note that the forged rockers have replaceable bushes, whereas the other two designs do not.

The pressed steel rocker listed here, 2A964, is the original 'small bore' A Series item; the 'big bore' (1275cc) equivalent listed elsewhere in the Somerford Mini
catalogue is 12G1313. The difference in theory between the two is a marginal increase in lift with the 'big bore' rocker, although in practice this is often swallowed
up by assembly tolerances. Concerning forged rockers, again originally there were small and big bore engine variants, but since the big bore item is the one
available (and it works perfectly well on a small bore engine), that's the one we list here. There were no small or big bore variants of the scintered rocker - one type
fitted all.

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
68	2A21	BUSH, rocker	8	Included in forged rocker.
69	5C2436	RIVET, bush to rocker	8	Included in forged rocker.
70	12A1215	SCREW, tappet adjusting	8	Use with pressed steel rocker.
71	6K654	NUT, locking screw	8	Use with pressed steel rocker.
72	AEG167	SCREW, tappet adjusting	8	Use with forged rocker.
73	NT605061	NUT, locking screw	8	Use with forged rocker.
74	12H3376	SCREW, tappet adjusting	8	Use with scintered rocker.
75	51K1178	NUT, locking screw	8	Use with scintered rocker.
76	6K556	SPRING, rocker spacing	3
77	2A18	WASHER, double coil, outer ends of shaft	2
78	6K555	WASHER, plain, outer ends of shaft	2
79	ZPS314	SPLIT PIN, outer ends of shaft	2

Valve Guides and Valve Seat Inserts
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
80	12G1111	GUIDE, inlet and exhaust valve	8	998cc (not Cooper); standard size.
	12G1111010	GUIDE, inlet and exhaust valve	8	998cc (not Cooper); 0.010" oversize.
	12A186	GUIDE, inlet and exhaust valve	8	998cc (Cooper) and 1098cc; standard size.
	12A186010	GUIDE, inlet and exhaust valve	8	998cc (Cooper) and 1098cc; 0.010" oversize.
81	2A639	INSERT, inlet valve seat	4	998cc standard size.
	AEA762	INSERT, inlet valve seat	4	998cc 1/16" oversize.
	12A392	INSERT, inlet valve seat	4	1098cc.
	TAM2152	INSERT, inlet valve seat	4	Lead free fuel compatible.
82	2A640	INSERT, exhaust valve seat	4	Standard size.
	AEA763	INSERT, exhaust valve seat	4	1/16" oversize; for leaded fuel use.
	TAM2068	INSERT, exhaust valve seat	4	Lead free fuel compatible.
Note that standard size and oversize inserts should not be mixed together on the same cylinder head.

Valves and Valve Springs
There are three types of collet used to retain valves in place on these engines and four types of valve to take them. The earlier valve designs
up to the early 1970s had a groove 1/4" deep into which the collets located, whereas later valves had a groove 1/8" deep, either 7/32" from the valve tip (early 1970s
to 1980) or 9/64" from the valve tip (the 1981 introduced A Plus type). Finally came the last variation, from 1984 onwards, where the collet located into an easily
identified triple groove on the valve. Care must be taken to ensure that valves, valve caps, valve springs and collets are matched before attempting reassembly.
Note also that while the early large groove collets were originally secured together with circlips, around 1969 these were judged to be adding nothing to the
security of the collets and were discontinued.

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

998cc (Not Cooper) 1963-74 approx
Valves With 1/4" Collet Groove
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
83	2A877	VALVE, inlet, 1 1/16" (27mm) dia.	4
84	AEA434	VALVE, exhaust, 1" (25.4mm) dia.	4
85	AEA311	SPRING, valve	8
86	2A11	SPLIT COLLET, pair, valve retaining	8
87	2A12	CIRCLIP, valve collet	8	1963-69; no longer fitted.
88	88G616	CAP, upper, valve spring	8
89	2A879	OIL SEAL, valve stem	8
90	2A545	SHROUD, valve guide	8	1963-69.

998cc (Cooper) 1963-69
Original Valves With 1/4" Collet Groove
Replacement Valves With 1/8" Collet Groove
Note that in the event of the original AEA400 exhaust valve not being available, the standard tune 998cc exhaust valve AEA434 may be substituted. Other replacement valves include 12G3034 and 12G3035 but since these have 1/8" collet grooves, 88G459 collets must be fitted with them.
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
91	12G296	VALVE, inlet, 1 7/32" (31mm) dia.	4	Original with 1/4" collet groove.
	12G3034	VALVE, inlet, 1 7/32" (31mm) dia.	4	Replacement with 1/8" collet groove.
92	AEA400	VALVE, exhaust, 1" (25.4mm) dia.	4	Original with 1/4" collet groove.
	AEA434	VALVE, exhaust, 1" (25.4mm) dia.	4	Replacement with 1/4" collet groove.
	12G3035	VALVE, exhaust, 1" (25.4mm) dia.	4	Replacement with 1/8" collet groove.
93	AEA311	SPRING, valve, outer	8
94	AEA401	SPRING, valve, inner	8
95	2A11	SPLIT COLLET, pair, valve retaining	8	Use with original 1/4" groove valves.
	88G459	SPLIT COLLET, pair, valve retaining	8	Use with replacement 1/8" groove valves.
96	2A12	CIRCLIP, valve collet	8	1963-69; no longer fitted.
97	88G616	CAP, upper, valve springs	8
98	AEA403	COLLAR, lower, valve springs	8
99	2A879	OIL SEAL, valve stem	8

998cc 1974 approx. to 1981
Valves With 1/8" Collet Groove, 7/32" From Valve Tip
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
100	CAM6391	VALVE, inlet, 1 1/16" (27mm) dia.	4
101	12A1987	VALVE, exhaust, 1" (25.4mm) dia.	4
102	AEA311	SPRING, valve	8
103	88G459	SPLIT COLLET, pair, valve retaining	8
104	88G616	CAP, upper, valve spring	8
105	2A879	OIL SEAL, valve stem	8	Not originally specified - fit if desired.
106	CAM6520	SHIM, valve spring	A/R

1098cc 1975-81
Valves With 1/8" Collet Groove, 7/32" From Valve Tip
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
107	12G3036	VALVE, inlet, 1 5/32" (29.4mm) dia.	4
108	12A1987	VALVE, exhaust, 1" (25.4mm) dia.	4
109	12G4287	SPRING, valve	8
110	88G459	SPLIT COLLET, pair, valve retaining	8
111	88G616	CAP, upper, valve spring	8
112	2A879	OIL SEAL, valve stem	8	Not originally specified - fit if desired.

998cc 1981-84
Valves With 1/8" Collet Groove, 9/64" From Valve Tip (A Plus Type)
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
113	CAM6502	VALVE, inlet, 1 1/16" (27mm) dia.	4
114	CAM6503	VALVE, exhaust, 1" (25.4mm) dia.	4
	CAM6505	VALVE, exhaust, 1" (25.4mm) dia., chrome stem	4	Lead free fuel compatible.
115	12G1015	SPRING, valve	8	High (10.3:1) compression ratio engines.
	AEA311	SPRING, valve	8	Low (8.3:1) compression ratio engines.
116	88G459	SPLIT COLLET, pair, valve retaining	8
117	88G617	CAP, upper, valve spring	8
118	ADU4905	OIL SEAL, valve stem	4/8
For a period, engines were fitted with oil seals on the inlet valve stems only, after which all valves wore them. Opinions differ on which is better - the choice is yours.

998cc 1984 On
Valves With Triple Collet Groove (A Plus Type)
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
119	TAM1062	VALVE, inlet, 1 1/16" (27mm) dia.	4	Lead free fuel compatible.
120	TAM1770	VALVE, exhaust, 1" (25.4mm) dia.	4	Lead free fuel compatible.
121	12G1015	SPRING, valve	8	High (10.3:1) compression ratio engines.
	AEA311	SPRING, valve	8	Low (8.3:1) compression ratio engines.
122	CAM6975	SPLIT COLLET, pair, valve retaining	8
123	AHU1897	CAP, upper, valve spring	8
124	ADU4905	OIL SEAL, valve stem	8

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Cylinder head - 998 and 1098cc

USE: 12A1987

VALVE-INLET-SMALL COLLET GROOVE 1 7/32'' 998 COOPER

VALVE-INLET-LARGE COLLET GROOVE-1 7/32'' 998 COOPER

PEDESTAL-ROCKER SHAFT WITH TAPPED HOLE

PEDESTAL-ROCKER SHAFT-WITH OIL HOLE

TUBE-AIR INJECTION PORT IN CYL. HEAD-CANADA & SWEDEN 75-80

ROCKER-FORGED- COOPER 'S' (reproduction)

GUIDE-INLET & EXHAUST VALVES-848 & 998 & 1275cc +010''

GUIDE-INLET & EXHAUST VALVES-848 & 998 & 1275cc

SPRING-VALVE-H.C. (10.3:1) ENGINES-998cc '81-'92 & 1275cc

ROCKER COVER-STEEL WITH BREATHER PIPE-'59-'69

SEAL-12A402 & 13H2296 OIL FILLER CAPS (included with cap)

We accept