Somerford Mini Ltd. Ordering Parts Using This Catalogue

Internal Engine - 970, 1071 and 1275cc (Cooper S)
No. Part No. Description Qty. Remarks No. Part No. Description Qty. Remarks
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 ra tio, dished crown)
Original Equipment 3 and 4 Ring Pistons
Within a very short period after the end of 1071cc engine production, the factor y 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 sketch y 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.
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
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 ra tio, dished crown)
Replacement 3 Ring and Powermax Pistons
5 21253STD PISTON SET, replacement metric 3 ring 1 Set of 4, standard size.
type
21253020 PISTON SET, replacement metric 3 ring 1 Set of 4, +0.020" oversize.
type
21253040 PISTON SET, replacement metric 3 ring 1 Set of 4, +0.040" oversize.
type
21253060 PISTON SET, replacement metric 3 ring 1 Set of 4, +0.060" oversize.
type
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 1 4 piston set, standard size.
pistons
R41570020 RING SET, for replacement metric 3 ring 1 4 piston set, +0.020" oversize.
pistons
R41570040 RING SET, for replacement metric 3 ring 1 4 piston set, +0.040" oversize.
pistons
R41570060 RING SET, for replacement metric 3 ring 1 4 piston set, +0.060" oversize.
pistons
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:
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 appropriate both for the 1071 and 1275cc engines are
identical in design but can be distinguished by the forging numbers displayed: AEG177 or AEG521 for an
AEG520 rod,and AEG625 for an AEG624 rod. 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!
11 AEG520 ROD ASS’Y, connecting (marked AEG177 4 1071 and 1275cc; original EN24V
or AEG521)
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, 1 Set of 4 pairs , standard size.
(‘big end bearings’)
8G2399010 BEARING SET, connecting rod, 1 Set of 4 pairs, 0.010" undersize.
(‘big end bearings’)
8G2399020 BEARING SET, connecting rod, 1 Set of 4 pairs, 0.020" undersize.
(‘big end bearings’)
8G2399030 BEARING SET, connecting rod, 1 Set of 4 pairs, 0.030" undersize.
(‘big end bearings’)
8G2399040 BEARING SET, connecting rod, 1 Set of 4 pairs, 0.040" undersize.
(‘big end bearings’)
Crankshaft
Crankshafts shown here are either assemblies (including main bearings , connecting rod bearings and thr ust
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. A
new forged crankshaft incorporating the most popular combination of Cooper S features (cross-drilled,
81.33mm stroke for 1275cc, in EN40B material) has been reintroduced in recent years with only minor
detail differences from the original item and new cranks are also available for 1071 and 970cc engines,
but machined from billets, not forgings. All three are special orders - please contact us for details.
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.
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
EN40B, nitrided, not cross-drilled AEG316.
38G402 CRANKSHAFT ASS’Y, with bearings, 1 1275cc, 1966-69. Stamped AEG479 or
EN40B, nitrided, cross-drilled
AEG480.
8G2739 CRANKSHAFT ASS’Y, with bearings, 1 1275cc, 1969-71. Stamped AEG623 or
EN16T, tuftrided, cross-drilled 12G1505.
28G234 CRANKSHAFT ASS’Y, with bearings, 1 970cc. Stamped AEG330.
EN40B, nitrided, not cross-drilled
Tel. 01249 721421 Fax. 01249 721316 www.somerford-mini.co.uk
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