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

Pistons, Piston Rings and Cylinder Liners
Note before ordering a piston set or ring set from Somerford Mini: a set of pistons consists of four pistons complete with rings and gudgeon pins; a set of rings
consists of sufficient rings for four pistons. Cylinder liners are supplied individually. Various piston upgrades (superior design and manufacture, different
capacities and compression ratios) are also available from Somerford Mini, but are only listed in this catalogue in instances where they make a good,
complication-free replacement for original specification pistons which are in short supply.

1071cc (9:1 compression ratio, dished crown)
Original Equipment 3 and 4 Ring Pistons
Within a very short period after the end of 1071cc engine production, the factory discontinued the original 3 ring pistons in favour of a 4 ring type - actually the
same pistons they were currently fitting in the 1275cc Cooper S engine. Today, supply of these 4 ring pistons is sketchy to say the least, and many owners
or engine builders use Powermax pistons or replacements with metric rings (listed later on this page). Both of the latter revert to having 3 rings per piston, but
these rings are not the same as the original 1071cc 3 rings and are not interchangeable with them.
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
1	AEG184STD	PISTON SET, original 3 ring type	1	Set of 4, standard size.
	AEG184010	PISTON SET, original 3 ring type	1	Set of 4, +0.010" oversize.
	AEG184020	PISTON SET, original 3 ring type	1	Set of 4, +0.020" oversize.
	AEG184040	PISTON SET, original 3 ring type	1	Set of 4, +0.040" oversize.
	AEG184060	PISTON SET, original 3 ring type	1	Set of 4, +0.060" oversize.
	8G2434STD	PISTON SET, replacement 4 ring type	1	Set of 4, standard size.
	8G2434010	PISTON SET, replacement 4 ring type	1	Set of 4, +0.010" oversize.
	8G2434020	PISTON SET, replacement 4 ring type	1	Set of 4, +0.020" oversize.
	8G2434040	PISTON SET, replacement 4 ring type	1	Set of 4, +0.040" oversize.
	8G2434060	PISTON SET, replacement 4 ring type	1	Set of 4, +0.060" oversize.
2	8G2435STD	RING SET, for original 3 ring pistons	1	4 piston set, standard size.
	8G2435010	RING SET, for original 3 ring pistons	1	4 piston set, +0.010" oversize.
	8G2435020	RING SET, for original 3 ring pistons	1	4 piston set, +0.020" oversize.
	8G2435040	RING SET, for original 3 ring pistons	1	4 piston set, +0.040" oversize.
	8G2435060	RING SET, for original 3 ring pistons	1	4 piston set, +0.060" oversize.
	BHM1165STD	RING SET, for replacement 4 ring pistons	1	4 piston set, standard size.
	BHM1165010	RING SET, for replacement 4 ring pistons	1	4 piston set, +0.010" oversize.
	BHM1165020	RING SET, for replacement 4 ring pistons	1	4 piston set, +0.020" oversize.
	BHM1165040	RING SET, for replacement 4 ring pistons	1	4 piston set, +0.040" oversize.
	BHM1165060	RING SET, for replacement 4 ring pistons	1	4 piston set, +0.060" oversize.

1275cc (9.75:1 compression ratio, dished crown)
Original Equipment 4 Ring Pistons
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
3	8G2434STD	PISTON SET, original 4 ring type	1	Set of 4, standard size.
	8G2434010	PISTON SET, original 4 ring type	1	Set of 4, +0.010" oversize.
	8G2434020	PISTON SET, original 4 ring type	1	Set of 4, +0.020" oversize.
	8G2434040	PISTON SET, original 4 ring type	1	Set of 4, +0.040" oversize.
	8G2434060	PISTON SET, original 4 ring type	1	Set of 4, +0.060" oversize.
4	BHM1165STD	RING SET, for original 4 ring pistons	1	4 piston set, standard size.
	BHM1165010	RING SET, for original 4 ring pistons	1	4 piston set, +0.010" oversize.
	BHM1165020	RING SET, for original 4 ring pistons	1	4 piston set, +0.020" oversize.
	BHM1165040	RING SET, for original 4 ring pistons	1	4 piston set, +0.040" oversize.
	BHM1165060	RING SET, for original 4 ring pistons	1	4 piston set, +0.060" oversize.

1071cc/1275cc (9:1/9.75:1 compression ratio, dished crown)
Replacement 3 Ring and Powermax Pistons
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
5	21253STD	PISTON SET, replacement metric 3 ring type	1	Set of 4, standard size.
	21253020	PISTON SET, replacement metric 3 ring type	1	Set of 4, +0.020" oversize.
	21253040	PISTON SET, replacement metric 3 ring type	1	Set of 4, +0.040" oversize.
	21253060	PISTON SET, replacement metric 3 ring type	1	Set of 4, +0.060" oversize.
	20747STD	PISTON SET, Powermax 3 ring type	1	Set of 4, standard size.
	20747020	PISTON SET, Powermax 3 ring type	1	Set of 4, +0.020" oversize.
	20747040	PISTON SET, Powermax 3 ring type	1	Set of 4, +0.040" oversize.
	20747060	PISTON SET, Powermax 3 ring type	1	Set of 4, +0.060" oversize.
6	R41570STD	RING SET, for replacement metric 3 ring pistons	1	4 piston set, standard size.
	R41570020	RING SET, for replacement metric 3 ring pistons	1	4 piston set, +0.020" oversize.
	R41570040	RING SET, for replacement metric 3 ring pistons	1	4 piston set, +0.040" oversize.
	R41570060	RING SET, for replacement metric 3 ring pistons	1	4 piston set, +0.060" oversize.
	R39380STD	RING SET, for Powermax 3 ring pistons	1	4 piston set, standard size.
	R39380020	RING SET, for Powermax 3 ring pistons	1	4 piston set, +0.020" oversize.
	R39380040	RING SET, for Powermax 3 ring pistons	1	4 piston set, +0.040" oversize.
	R39380060	RING SET, for Powermax 3 ring pistons	1	4 piston set, +0.060" oversize.

970cc (10:1 compression ratio, flat crown)
Original Equipment 4 Ring Pistons
While the 1071cc and 1275cc Cooper S engines share the same dished crown pistons, the 970cc engine has a unique flat crown design:
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
7	8G2432STD	PISTON SET, original 4 ring type	1	Set of 4, standard size.
	8G2432010	PISTON SET, original 4 ring type	1	Set of 4, +0.010" oversize.
	8G2432020	PISTON SET, original 4 ring type	1	Set of 4, +0.020" oversize.
	8G2432040	PISTON SET, original 4 ring type	1	Set of 4, +0.040" oversize.
	8G2432060	PISTON SET, original 4 ring type	1	Set of 4, +0.060" oversize.
8	BHM1165STD	RING SET, for original 4 ring pistons	1	4 piston set, standard size.
	BHM1165010	RING SET, for original 4 ring pistons	1	4 piston set, +0.010" oversize.
	BHM1165020	RING SET, for original 4 ring pistons	1	4 piston set, +0.020" oversize.
	BHM1165040	RING SET, for original 4 ring pistons	1	4 piston set, +0.040" oversize.
	BHM1165060	RING SET, for original 4 ring pistons	1	4 piston set, +0.060" oversize.
9	AEG189	PIN, gudgeon	4	Included in piston sets.
10	AEG428	LINER, cylinder	4	Standard size.

Connecting Rods and Crankshaft
Connecting Rods
Telling a 970cc connecting rod apart from the 1071/1275cc item is a matter of measuring the distance between small and big end centres: at 5 7/8" the 970cc
rod is 1/8" longer than that used in the larger capacity engines. The two different material rods for the 1071 and 1275cc engines are identical in design but can
be distinguished by the forging numbers displayed. AEG624 is a good substitute for the original AEG520 rod (it was developed for the 1275cc MG Midget/Austin
Healey Sprite engine), but as always make sure all four you intend to use are the same!
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
11	AEG520	ROD ASS'Y, connecting (marked AEG177 or AEG521)	4	1071 and 1275cc; original EN24V material.
	AEG624	ROD ASS'Y, connecting (marked AEG625)	4	1071 and 1275cc; replacement in EN21 material.
	AEG309	ROD ASS'Y, connecting	4	970cc.
12	AEG519	BOLT, connecting rod cap ('big end')	8	Included in connecting rod assembly.
13	AEG147	NUT, connecting rod cap ('big end')	8	Included in connecting rod assembly.
14	8G2399STD	BEARING SET, connecting rod ('big end bearings')	1	Set of 4 pairs, standard size.
	8G2399010	BEARING SET, connecting rod ('big end bearings')	1	Set of 4 pairs, 0.010" undersize.
	8G2399020	BEARING SET, connecting rod ('big end bearings')	1	Set of 4 pairs, 0.020" undersize.
	8G2399030	BEARING SET, connecting rod ('big end bearings')	1	Set of 4 pairs, 0.030" undersize.
	8G2399040	BEARING SET, connecting rod ('big end bearings')	1	Set of 4 pairs, 0.040" undersize.

Crankshaft
Crankshafts shown here are either assemblies (including main bearings, connecting rod bearings and thrust washers), or bare (without bearings or thrust washers).
However, please note that new crankshafts may be supplied complete with bearings but other times not, depending on what is available at the time. Additionally
Somerford Mini can offer a crankshaft regrinding service, usually carried out on your old unit. You should enquire on the current status of supply before ordering a
crankshaft from Somerford Mini.

For details of the primary gear and its bushes located on the tail of the crankshaft, please see the 'Manual Gearbox - Primary, Idler and Drive Gears' section in the Transmissions area of the Somerford Mini catalogue.
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
15	38G343	CRANKSHAFT ASS'Y, with bearings,	1	1071cc. Stamped AEG171.
		EN40B, nitrided, not cross-drilled
	38G357	CRANKSHAFT ASS'Y, with bearings,	1	1275cc, 1964-66. Stamped AEG315 or AEG316.
		EN40B, nitrided, not cross-drilled
	38G402	CRANKSHAFT ASS'Y, with bearings,	1	1275cc, 1966-69. Stamped AEG479 or AEG480.
		EN40B, nitrided, cross-drilled
	8G2739	CRANKSHAFT ASS'Y, with bearings,	1	1275cc, 1969-71. Stamped AEG623 or 12G1505.
		EN16T, tuftrided, cross-drilled
	28G234	CRANKSHAFT ASS'Y, with bearings,	1	970cc. Stamped AEG330.
		EN40B, nitrided, not cross-drilled
16	AEG170	CRANKSHAFT, bare,	1	1071cc. Stamped AEG171.
		EN40B, nitrided, not cross-drilled
	AEG315	CRANKSHAFT, bare,	1	1275cc, 1964-66. Stamped AEG315 or AEG316.
		EN40B, nitrided, not cross-drilled
	AEG479	CRANKSHAFT, bare,	1	1275cc, 1966-69. Stamped AEG479 or AEG480.
		EN40B, nitrided, cross-drilled
	AEG622	CRANKSHAFT, bare,	1	1275cc, 1969-71. Stamped AEG623 or 12G1505.
		EN16T, tuftrided, cross-drilled
	AEG329	CRANKSHAFT, bare,	1	970cc. Stamped AEG330.
		EN40B, nitrided, not cross-drilled
17	1G1167	RESTRICTOR, oil	1	Included in AEG170, AEG315 and AEG329 crankshafts.
	AEG420	RESTRICTOR, oil	1	Included in AEG479 and AEG622 crankshafts.
18	8G2391STD	BEARING SET, main bearings, set of 3 pairs	1	Standard size.
	8G2391010	BEARING SET, main bearings, set of 3 pairs	1	0.010" undersize.
	8G2391020	BEARING SET, main bearings, set of 3 pairs	1	0.020" undersize.
	8G2391030	BEARING SET, main bearings, set of 3 pairs	1	0.030" undersize.
	8G2391040	BEARING SET, main bearings, set of 3 pairs	1	0.040" undersize.

Thrust washers are supplied as a pair; i.e. one upper and one lower thrust washer. Two pairs are required per engine, fitted selectively to obtain the correct amount of end float on the crankshaft.
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
19	BHM1293STD	THRUST WASHERS, crankshaft, pair	A/R	Standard size.
	BHM1293003	THRUST WASHERS, crankshaft, pair	A/R	+0.003" oversize.
	BHM1293005	THRUST WASHERS, crankshaft, pair	A/R	+0.005" oversize.
	BHM1293030	THRUST WASHERS, crankshaft, pair	A/R	+0.030" oversize.
20	6K836	KEY, Woodruff, crankshaft	1
21	AEA695	GEAR, steel, timing chain, crankshaft	1	1963-70.
	12G1699	GEAR, iron, timing chain, crankshaft	1	1970-71.
22	6K628	WASHER, packing	A/R
23	12A1148	OIL THROWER, crankshaft	1
24	88G561	OIL SEAL, timing cover	1	Included in timing cover assembly.

Crankshaft Pulley
The 1071, 1275 and 970cc Cooper S engines used two different vibration damper pulleys during their production lives. The original design was a separate
pulley with a damper screwed to it; eventually a one-piece damper pulley was offered as a replacement and was also in fact fitted to all 1969-71 engines.
Both set ups remained available as spares for many years. If you want the original pulley, it is still available today from Somerford Mini.

Crankshaft Pulley 1963-69
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
25	AEG454	PULLEY, crankshaft	1	Separate pulley and damper fitment.
26	12A367	DAMPER	1	Separate pulley and damper fitment.
27	SH605051	SCREW, damper to pulley	4	Separate pulley and damper fitment.
28	LWZ305	WASHER, locking	4	Separate pulley and damper fitment.
29	AEA312	BOLT, pulley to crankshaft	1	Separate pulley and damper fitment.
30	12A398	LOCK TAB, pulley bolt	1	Separate pulley and damper fitment.
31	88G305	PULLEY, crankshaft, with damper	1	One-piece damper pulley fitment.
32	12A283	BOLT, pulley to crankshaft	1	One-piece damper pulley fitment.
33	12A398	LOCK TAB, pulley bolt	1	One-piece damper pulley fitment.

Crankshaft Pulley 1969-71
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
34	88G305	PULLEY, crankshaft, with damper	1
	CAM4929	PULLEY, crankshaft, with damper	1	May be used to replace 88G305.
35	12A283	BOLT, pulley to crankshaft	1
36	12A398	LOCK TAB, pulley bolt	1

Camshaft and Tappets
A range of uprated camshafts and other engine tuning components are also available from Somerford Mini, but are not listed here. Please contact us for details.

Camshaft
The standard fitment Cooper S camshafts can be easily distinguished from each other. AEG542 alone is designed for a 'star' drive oil pump and accepts the
necessary drive flange in its end. The other two ('pin drive') cams can be told apart by AEG510 having a single machined identification ring standing proud from
the shaft, one lobe up from the distributor gear; AEG148 does not have this ring. AEG542 also has a single, but broader, identification ring. All Cooper S
camshafts, in common with most other high performance A Series camshafts, have 1/2" wide lobes.
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
37	AEG148	CAMSHAFT, for 'pin drive' oil pump	1	1071cc and 970cc. 1275cc 1964-66.
	AEG510	CAMSHAFT, for 'pin drive' oil pump	1	1275cc 1966-69.
	AEG542	CAMSHAFT, for 'star drive' oil pump	1	1275cc 1969-71.
38	2A299	PIN, oil pump drive	1	Included in 'pin drive' type camshafts.
39	CHM108	FLANGE, for 'star drive' oil pump (flange also known as 'spider')	1	Use with 'star drive' type camshaft.
40	12G4499	SPINDLE, distributor drive	1
41	2A13	TAPPET, without oil hole	8	1963-68; standard size.
	2A13010	TAPPET, without oil hole	8	1963-68; +0.010" oversize.
	AEG584	TAPPET, with oil hole	8	1968-71; standard size.
	AEG584010	TAPPET, with oil hole	8	1968-71; +0.010" oversize.
	AEG584020	TAPPET, with oil hole	8	1968-71; +0.020" oversize.
Tappets with or without oil holes are interchangeable, but only in full engine sets.

Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
42	2A14	PUSH ROD	8	1071cc and 970cc. Alternative to 12A250 when replaced in sets.
	12A250	PUSH ROD	8	1071cc and 970cc. Alternative to 2A14 when replaced in sets.
	AEG314	PUSH ROD	8	1275cc.

Timing Chain
Ill. No.	Part No.	Description	Qty. Rqd.	Remarks
43	2H4905	CHAIN, timing, duplex (double row)	1
44	AEA696	GEAR, steel, duplex timing chain, camshaft	1	1963-70.
	12G1397	GEAR, iron, duplex timing chain, camshaft	1	1970-71.
45	WKN505	KEY, Woodruff	1
46	6K629	NUT, gear to camshaft	1
47	2A759	LOCK TAB, nut	1

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

USE: 21253020

USE: 21253010

CRANKSHAFT EN40B NITRIDED NOT X DRILLED 1275 'S' '64-'66

CAMSHAFT-970 & 1071 'S' AND 1275 'S' '64-'66

NUT-BIG END CAP- COOPER 'S'

GEAR-STEEL-CAMSHAFT-DUPLEX TIMING CHAIN genuine bmc

GEAR-STEEL-DUPLEX TIMING CHAIN-CRANKSHAFT-COOPER 'S'

BOLT-PRESSED & TWO PIECE CRANKSHAFT PULLEYS

CRANKSHAFT & BEARINGS EN16T TUFTRIDED X DRILLED 1275 S 69-71

USE: BHM1628STD

USE: BHM1628060

USE: BHM1628040

We accept