External engine - 970, 1071 and 1275cc (cooper s)

970, 1071 and 1275cc Cooper S Engine Identification
The big bore A Series engine, of which by far the most common variant was the 1275cc unit, was initially developed specifically for the Cooper S, although in
modified forms it later saw use in large numbers in other BMC, Leyland and Austin Rover vehicles as well as other Minis. Rather than drawing on the 848cc Mini
engine for its parentage, it was in fact developed from the 948cc A Series (of which there were never any transverse versions) previously seen in such cars as the
Morris Minor, Austin A35 and Austin Healey Sprite.

The first incarnation of the big bore A Series engine was the 1071cc Cooper S unit, introduced in 1963 and produced for just 18 months. It was joined in early
1964 and eventually replaced by the very popular 1275cc engine, which ran all the way through to the demise of the Cooper S in 1971. Additionally, the
competitions-intended 'homologation special' 970cc engine, sharing most of its features with its larger capacity siblings, was produced for just under a year
between 1964 and 1965. These three Cooper S engines are almost unique in A Series engine history in that they were never fitted in any other model of car. It
is important to note therefore that the 1275cc Cooper S unit is quite different to engines of the same capacity used in later Minis. The latter 'solid wall block' (i.e.
without tappet chest covers) 1275 engines are described in the 'External Engine - 1275cc (Not Cooper S)' section of the Somerford Mini catalogue.

Upon opening the bonnet, the most obvious feature denoting the presence of a Cooper S power unit is the so-called 'eleven stud' cylinder head, technically a misnomer
because the head is fixed to the block by ten studs and a bolt (the norm for an A Series engine is nine studs). The extra two fixings are at either end of the rocker
cover and impinge slightly on the rocker cover's sealing flange. Do not take this feature on its own as evidence of a genuine Cooper S engine, however - a small
number of other BMC and Leyland products like the Austin/Morris 1300 GT also had the 'eleven stud' head. There are a myriad of other easily recognisable features
which make up a Cooper S engine, like the aforementioned tappet chest covers which are not present on any other big bore A Series and, once the inside of the
engine is open to inspection, the main bearing caps being secured by studs and nuts rather than the usual bolts. Of course there was also the fabled EN40B nitrided
steel crankshaft, unique to the Cooper S but not in fact fitted to all Cooper S engines: it was dropped quietly in a cost cutting measure in 1969, leaving engines
produced in the last couple of years to 'make do' with the still pretty desirable tuftrided EN16 crankshaft shared, again, with the Austin/Morris 1300 GT.

Engine serial number prefix codes are important in identifying what you have in your car and establishing which replacement parts to fit to it. The 970, 1071 and
1275cc engine number prefixes used on Mini Cooper S engines are listed here for that reason. Care should however be taken when dealing with 1071cc engine
numbers as until the end of 1963 both their prefix codes and serial numbers coincide with those allocated to Cooper 997cc engines! The engine serial number is
stamped on a plate affixed to the cylinder head mating face or 'deck' of the cylinder block, at the front of the engine towards the right hand side, as you look at the
engine in the car. Note that the last code letter before the serial number itself always relates to the compression ratio of the engine. Cooper S engines were always
classified as high compression, but depending on capacity different compression ratio codes were issued: X for 970cc (10:1 CR), H for 1071cc (9:1 CR) and Y for
1275cc (9.75:1 CR). No compression ratio code was shown on '12H' type engine numbers used between 1969 and 1971.

Factory reconditioned engines always lost their serial numbers in favour of an engine number plate stamped with the appropriate part number for the intended
application for each engine. In the absence of an engine serial number on a factory reconditioned unit, this is the only means of identification - but beware!
Factory reconditioned engines were more often than not built up with whatever suitable components were to hand; for example, new parts were usually plucked from
the engine production line and were therefore of the latest design. Reused components came from stocks of parts which would do the same job, but were not
necessarily the same design, all lumped together. In other words, parts used in the rebuild were frequently incorrect in an historic sense for the engine being rebuilt.

Cooper S Engine Serial Number Prefix Codes
9F/SA/X	970cc engine without closed circuit breathing (1964)
9FD/SA/X	970cc engine with closed circuit breathing (1964)
9FE/SA/X	970cc engine with closed circuit breathing and warning switch type oil filter head (1964)
9F/SA/X	970cc engine, specification as 9FE/SA/X. Code letter 'E' dropped for remainder of production (1964-65)
9F/SA/H	1071cc engine without closed circuit breathing (1963-64)
9FD/SA/H	1071cc engine with closed circuit breathing (1964)
9F/SA/Y	1275cc engine without closed circuit breathing (1964)
9FD/SA/Y	1275cc engine with PCV valve closed circuit breathing (1964)
9F/SA/Y	1275cc engine with PCV valve closed circuit breathing. Code letter 'D' dropped for remainder of production (1964-68)
9F/XE/Y	1275cc engine with PCV valve closed circuit breathing and 4 synchro gearbox (1968-69)
12H/397/	1275cc engine with carburetter crankcase closed circuit breathing, 4 synchro gearbox, EN16 crank and dynamo (1969-71)
12H/398/	1275cc engine with carburetter crankcase closed circuit breathing, 4 synchro gearbox, EN16 crank and alternator (1969-71)

BMC/Leyland/Unipart Cooper S Reconditioned Engine Part Numbers
8G38	970cc engine without closed circuit breathing (1964)
8G41	970cc engine with closed circuit breathing (1964)
8G46	970cc engine with closed circuit breathing and warning switch type oil filter head (1964-65)
8G133	1071cc engine without closed circuit breathing (1963-64)
8G153	1071cc engine with closed circuit breathing (1964)
8G145	1275cc engine without closed circuit breathing, with AEG148 camshaft (1964)
8G154	1275cc engine with PCV valve closed circuit breathing and AEG148 camshaft (1964)
8G155	1275cc engine with PCV valve closed circuit breathing, AEG148 camshaft and warning switch type oil filter head (1964-66)
8G174	1275cc engine with PCV valve closed circuit breathing, AEG510 camshaft and warning switch type oil filter head (1966-69)
38G464	1275cc engine with carburetter crankcase closed circuit breathing, AEG542 camshaft and EN16 crankshaft (1969-71)
The last number, 38G464, became by the mid-1970s a 'one spec. fits all' engine, superseding all previous 1275cc Cooper S reconditioned engine specifications.
However, it still usually contained an AEG542 camshaft and EN16 crankshaft.

Rebuilt or Repaired 970, 1071 and 1275cc Engine Assemblies
Somerford Mini Ltd. offers an engine rebuilding and repair service, courtesy of its workshop facility. We can carry out repairs or rebuilds on late-model
engines, but the extent of rebuilding on an early engine is governed by - and sometimes restricted by - parts availability.
Please contact us to discuss your Mini engine requirements - it would be helpful if you could supply us not only the details of what's gone wrong with
your engine, but also the full engine number (if known) and type (capacity, high or low compression, gearbox, breathing system, etc.). The more you
can provide us with, the better we can ascertain how we might possibly help you.

Gasket Sets
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
1	GUG49	GASKET SET, conversion ('bottom end set')	1
A conversion gasket set (often called 'bottom end' or 'supplementary' sets) includes gaskets for the following: water pump, front cover, tappet chest covers, front
mounting plate, oil pump, oil filter head, engine to gearbox joint and flywheel/torque converter housing. Washers, seals and O rings are included for the following:
priming plug, drain tap/plug, main bearing cap, front cover, tappet chest covers, distributor housing and oil suction pipe. Note that the tappet chest cover gaskets
included are the post-1966 rubber type - customers requiring the earlier cork gaskets should purchase them separately.
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
	EGS001	GASKET SET, full engine	1
The full engine gasket set includes the conversion gasket set listed above plus a cylinder head gasket set ('decoke' or 'decarbonising' set) minus the head gasket itself, which should be purchased separately according to the engine size.

External Engine Components
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
2	AEH592	PLUG, core (welch), cylinder block, 1 41/64" dia.	4
3	2K1345	PLUG, oil pressure release valve passage	2
4	12H1734	PLUG, oil gallery	2
5	AEG183	PLUG, tapered, tappet chest	2
6	1A1964	RESTRICTOR, cam bearing oil feed	1
7	CAM150	STUD, cylinder head, long	4
8	CAM151	STUD, cylinder head, short	6
9	AEA684	INSERT, helicoil, cylinder head bolt	1	If required.

The fuel pump drive aperture is not present on the vast majority of Cooper S cylinder block castings. In fact, we've never seen one with the aperture, but the original 1960s Cooper parts books consistently list the blanking plate for it, so perhaps it was present on some engines. However, even when it isn't there, one of the studs which would have been used to secure the aperture blanking plate is still fitted - primarily to hold the vent pipe on open circuit breathing engines, but also sometimes used to secure an engine size identification plate.
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
10	CHS2513	STUD, fuel pump drive aperture	2/1	Qty. 1 required if fuel pump drive aperture is not present.
11	2A265	PLATE, blanking fuel pump drive aperture	1	Not required if fuel pump drive aperture is not present.
12	GUG705557GM	GASKET, blanking plate	1	Not required if fuel pump drive aperture is not present.
13	FNZ105	NUT, blanking plate to block	2/1	Qty. 1 required if fuel pump drive aperture is not present.
14	LWZ205	WASHER, locking	2/1	Qty. 1 required if fuel pump drive aperture is not present.
15	PWZ105	WASHER, plain	1	Required for open circuit breathing vent pipe bracket (if fitted).
16	53K615	STUD, oil filter head	2
17	AEG156	SCREW, main bearing cap to block	6	1071cc.
18	AEG205	LOCK TAB, main bearing cap screw	6	1071cc.
19	12G478	STUD, main bearing cap to block, front and rear	4	970 and 1275cc.
20	AEG323	STUD, main bearing cap to block, centre	2	970 and 1275cc.
21	AEG417	NUT, main bearing cap	6	970 and 1275cc; std. fitment.
	CAJJ4013	NUTS, main bearing cap, set of 6	1	970 and 1275cc; competition.
22	BHM1210	LINER SET, camshaft bearings	1
23	3H576	TAP, cooling system drain	1	Standard fitment 1963-69.
24	2K4954B	WASHER, fibre, drain tap	A/R	Use with drain tap.
This washer not only seals the tap to the block, but also is intended (using whatever quantity is necessary) to shim the tap so that when tightly screwed to the block the spout faces downwards.

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
25	53K2853	PLUG, cooling system drain	1	Standard fitment 1969 on. Alternative to drain tap.
26	6K638B	WASHER, sealing plug	1	Use with drain plug.
27	2A612	HOUSING, distributor	1	1963-65; does not require O ring.
28	12A1136	HOUSING, distributor	1	1965 on; requires O ring.
29	13H2792	O RING, housing	1	1965 on.
The later 12A1136 distributor housing may be fitted in place of the earlier 2A612 housing, but only if a 13H2792 O ring is fitted with it.

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
30	SH604061	SCREW, housing to block	2
31	LWZ404	WASHER, shakeproof	2

Engine Front Mounting Plate
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
32	AEG161	PLATE, engine front mounting	1
33	12G619B	GASKET, plate to block	1
34	SH605051	SCREW, plate to block	2
35	LWZ305	WASHER, locking	2
36	AEA687	SCREW, plate to main bearing cap	2
37	AHU2379	PLATE, camshaft locating	1
38	SH604061	SCREW, plate to block	3
39	WF600040	WASHER, shakeproof	3

Timing Cover
Several timing covers were fitted in the 1960s, some with timing pointers, some without, most with stiffeners, one without. All were superseded by 1970 by 12G2506, which includes a timing pointer and lower stiffener and does not require the stiffener 12A666 listed below.
The plain washers PWZ104 and PWZ105 listed below replace the original elongated washers used at different times on the A Series engine until the 1980s.
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
40	12G2506	COVER, front, timing	1	Includes oil seal.
41	88G561	OIL SEAL, timing cover	1	Included in timing cover.
42	12A666	STIFFENER, timing cover	1	Use on early 1960s covers suffering from poor sealing.
43	12A956	GASKET, timing cover	1
44	SH604031	SCREW, timing cover to front mounting plate	6
45	LWZ204	WASHER, locking	6
46	PWZ104	WASHER, plain	6/3	Qty. reduced when stiffener is present.
47	SH605061	SCREW, timing cover to mounting plate and block	4
48	LWZ305	WASHER, locking	4
49	PWZ105	WASHER, plain	4/3	Qty. reduced when stiffener is present.

Tappet Chest Covers
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
50	-	COVER, tappet chest, LH, with breather pipe	1	Convex cover; for open circuit breathing (1963-64).
51	-	COVER, tappet chest, LH, with breather pipe	1	Concave replacement cover; for open circuit breathing (1963-64).
52	12G577	COVER, tappet chest, LH, with oil separator	1	Convex cover; for closed circuit breathing (1964-66).
53	12A1212	COVER, tappet chest, LH, with oil separator	1	Concave cover; for closed circuit breathing (1966 on).
There are too many varieties of LH tappet chest cover for open circuit engine breathing models to list here. However they are all detailed, along with all of the other components of each type of breathing system, in the 'Emission Controls - Engine Breathing' sections in the Fuel and Exhaust Systems area of the Somerford Mini catalogue.

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
54	12H941	COVER, tappet chest, RH	1	Convex cover, 1963-66.
55	12A1386	COVER, tappet chest, RH	1	Concave cover, 1966 on.
56	12A1139	GASKET, cover, cork	1	For convex type cover.
57	BH605151	BOLT, cover to block	1	For convex type cover.
58	2K4958	WASHER, bolt	1	For convex type cover.
59	GUG705505GM	GASKET, cover, rubber	1	For concave type cover.
60	SH605091	SCREW, cover to block	1	For concave type cover.
61	12A1177	WASHER, cup	1	For concave type cover.
62	12A1176	BUSH, rubber	1	For concave type cover.
63	MRC1980A	BUSH, rubber	1	Later design; replaces 12A1176 and 12A1177.

Oil System Components
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
64	2K4994	PLUG, priming	1
65	6K464	WASHER, sealing	1
66	12H865	PLUNGER, oil pressure relief valve	1	Standard fitment.
67	BLS916	BALL, oil pressure relief valve	1	Alternative; see note below.
The ball above may be used in place of the standard fitment plunger to guard against a sticking relief valve (something that the plunger is prone to do, given dirt or metal particles in the oil).

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
68	AEA536	SPRING, oil pressure relief valve	1
69	12A1851	CAP, threaded, relief valve	1
70	6K431	WASHER, sealing	1
71	2A797	HOUSING, oil pressure relief valve	1	Press-fit in cylinder block.
72	12A116	DIPSTICK, oil level	1	1963-66.
	12A1263	DIPSTICK, oil level	1	1966 on.
73	AEC671	WASHER, sealing dipstick	1	1963-66.
	12A1262	WASHER, sealing dipstick	1	1966 on.
74	12G107	TUBE, dipstick, nylon	1	1963-66.
	12A1261	TUBE, dipstick, metal	1	1966 on.

Request a free catalogue

Click here

Body panel
catalogue

Click here

Accessories
catalogue

Monday:	09.00am to 17.30pm
Tuesday:	09.00am to 17.30pm
Wednesday:	09.00am to 17.30pm
Thursday:	09.00am to 17.30pm
Friday:	09.00am to 17.30pm
Saturday:	09.00pm to 12.00pm

External engine - 970, 1071 and 1275cc (cooper s)

GASKET-TIMING BACKPLATE-PRE A+

NUT SET (6) -MAINS CAP-COOPER 'S'

WASHER-FIBRE, CONVEX TAPPET CHEST COVER BOLT

USE: LWZ404

SET SCREW-5/16 UNF x 1 1/8''

SEAL-TAPPET CHEST COVER-REPLACES 12A1177 & 12A1176

USE: GUG705779GM

GASKET-TAPPET CHEST COVER-RUBBER

GASKET SET CONVERSION-MANUAL ALL MODELS

GASKET SET-ENGINE AND GEARBOX ( no head gasket)- MOST MODELS

STUD-5/16 UNF/UNC x 1 5/8''

STUD-CYLINDER HEAD-SHORT (5 required except S)

We accept