Pistons, Piston Rings and Cylinder Liners |
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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. |
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998cc 1963-80 (not Cooper) |
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4 Ring Piston With 0.125" Thick Double Bevelled Oil Ring |
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Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
1 |
12A673STD |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, standard size. |
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12A673020 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.020" oversize. |
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12A673030 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.030" oversize. |
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12A673040 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.040" oversize. |
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12A673060 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.060" oversize. |
2 |
BHM1162STD |
RING SET, 4 piston set |
1 |
Standard size. |
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BHM1162020 |
RING SET, 4 piston set |
1 |
+0.020" oversize. |
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BHM1162030 |
RING SET, 4 piston set |
1 |
+0.030" oversize. |
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BHM1162040 |
RING SET, 4 piston set |
1 |
+0.040" oversize. |
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BHM1162060 |
RING SET, 4 piston set |
1 |
+0.060" oversize. |
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998cc 1980-84 (A Plus) |
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4 Ring Piston With 0.158" Thick Special Oil Ring |
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Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
3 |
ADU3920STD |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, standard size. |
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ADU3920020 |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, +0.020" oversize. |
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ADU3920030 |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, +0.030" oversize. |
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ADU3920040 |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, +0.040" oversize. |
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ADU3920060 |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, +0.060" oversize. |
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ADU3922STD |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, standard size. |
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ADU3922020 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.020" oversize. |
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ADU3922030 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.030" oversize. |
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ADU3922040 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.040" oversize. |
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ADU3922060 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.060" oversize. |
4 |
BHM1281STD |
RING SET, 4 piston set |
1 |
Standard size. |
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BHM1281020 |
RING SET, 4 piston set |
1 |
+0.020" oversize. |
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BHM1281030 |
RING SET, 4 piston set |
1 |
+0.030" oversize. |
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BHM1281040 |
RING SET, 4 piston set |
1 |
+0.040" oversize. |
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BHM1281060 |
RING SET, 4 piston set |
1 |
+0.060" oversize. |
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998cc 1984-88 (A Plus) |
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3 Ring Piston With Gudgeon Pin Retained By Circlips |
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Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
5 |
ADU3490STD |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, standard size. |
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ADU3490020 |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, +0.020" oversize. |
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ADU3490030 |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, +0.030" oversize. |
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ADU3490040 |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, +0.040" oversize. |
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ADU3490060 |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, +0.060" oversize. |
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ADU4203STD |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, standard size. |
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ADU4203020 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.020" oversize. |
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ADU4203030 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.030" oversize. |
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ADU4203040 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.040" oversize. |
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ADU4203060 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.060" oversize. |
6 |
BHM1415STD |
RING SET, 4 piston set |
1 |
Standard size. |
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BHM1415020 |
RING SET, 4 piston set |
1 |
+0.020" oversize. |
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BHM1415030 |
RING SET, 4 piston set |
1 |
+0.030" oversize. |
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BHM1415040 |
RING SET, 4 piston set |
1 |
+0.040" oversize. |
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BHM1415060 |
RING SET, 4 piston set |
1 |
+0.060" oversize. |
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998cc 1988 On (A Plus) |
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3 Ring Piston With Press Fit Gudgeon Pin |
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Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
7 |
TAM2052STD |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, standard size. |
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TAM2052020 |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, +0.020" oversize. |
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TAM2052030 |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, +0.030" oversize. |
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TAM2052040 |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, +0.040" oversize. |
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TAM2052060 |
PISTON SET, set of 4, flat piston crown |
1 |
10.3:1 compression ratio, +0.060" oversize. |
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TAM2054STD |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, standard size. |
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TAM2054020 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.020" oversize. |
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TAM2054030 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.030" oversize. |
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TAM2054040 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.040" oversize. |
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TAM2054060 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.060" oversize. |
8 |
BHM1629STD |
RING SET, 4 piston set |
1 |
Standard size. |
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BHM1629020 |
RING SET, 4 piston set |
1 |
+0.020" oversize. |
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BHM1629030 |
RING SET, 4 piston set |
1 |
+0.030" oversize. |
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BHM1629040 |
RING SET, 4 piston set |
1 |
+0.040" oversize. |
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BHM1629060 |
RING SET, 4 piston set |
1 |
+0.060" oversize. |
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998cc 1963-69 (Cooper) |
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4 Ring Piston |
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Note that the 9:1 compression ratio Cooper pistons have been out of production for many years and supply of this type is therefore almost non-existant. The Powermax pistons listed further down the page are most often supplied as replacements. |
Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
9 |
12A674STD |
PISTON SET, set of 4, raised 'D' piston crown |
1 |
9:1 compression ratio, standard size. |
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12A674020 |
PISTON SET, set of 4, raised 'D' piston crown |
1 |
9:1 compression ratio, +0.020" oversize. |
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12A674030 |
PISTON SET, set of 4, raised 'D' piston crown |
1 |
9:1 compression ratio, +0.030" oversize. |
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12A674040 |
PISTON SET, set of 4, raised 'D' piston crown |
1 |
9:1 compression ratio, +0.040" oversize. |
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12A674060 |
PISTON SET, set of 4, raised 'D' piston crown |
1 |
9:1 compression ratio, +0.060" oversize. |
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12A593STD |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, standard size. |
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12A593020 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.020" oversize. |
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12A593030 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.030" oversize. |
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12A593040 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.040" oversize. |
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12A593060 |
PISTON SET, set of 4, dished piston crown |
1 |
8.3:1 compression ratio, +0.060" oversize. |
10 |
BHM1162STD |
RING SET, 4 piston set |
1 |
Standard size. |
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BHM1162020 |
RING SET, 4 piston set |
1 |
+0.020" oversize. |
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BHM1162030 |
RING SET, 4 piston set |
1 |
+0.030" oversize. |
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BHM1162040 |
RING SET, 4 piston set |
1 |
+0.040" oversize. |
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BHM1162060 |
RING SET, 4 piston set |
1 |
+0.060" oversize. |
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998cc 1963-69 (Cooper) |
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3 Ring Powermax Piston |
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Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
11 |
20950STD |
PISTON SET, set of 4, flat piston crown |
1 |
9.7:1 compression ratio, standard size. |
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20950020 |
PISTON SET, set of 4, flat piston crown |
1 |
9.7:1 compression ratio, +0.020" oversize. |
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20950040 |
PISTON SET, set of 4, flat piston crown |
1 |
9.7:1 compression ratio, +0.040" oversize. |
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20950060 |
PISTON SET, set of 4, flat piston crown |
1 |
9.7:1 compression ratio, +0.060" oversize. |
12 |
R39400STD |
RING SET, 4 piston set |
1 |
Standard size. |
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R39400020 |
RING SET, 4 piston set |
1 |
+0.020" oversize. |
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R39400040 |
RING SET, 4 piston set |
1 |
+0.040" oversize. |
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R39400060 |
RING SET, 4 piston set |
1 |
+0.060" oversize. |
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1098cc 1975-80 |
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4 Ring Piston With 0.125" Thick Double Bevelled Oil Ring |
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Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
13 |
12G758STD |
PISTON SET, set of 4, dished piston crown |
1 |
8.5:1 compression ratio, standard size. |
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12G758020 |
PISTON SET, set of 4, dished piston crown |
1 |
8.5:1 compression ratio, +0.020" oversize. |
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12G758030 |
PISTON SET, set of 4, dished piston crown |
1 |
8.5:1 compression ratio, +0.030" oversize. |
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12G758040 |
PISTON SET, set of 4, dished piston crown |
1 |
8.5:1 compression ratio, +0.040" oversize. |
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12G758060 |
PISTON SET, set of 4, dished piston crown |
1 |
8.5:1 compression ratio, +0.060" oversize. |
14 |
BHM1162STD |
RING SET, 4 piston set |
1 |
Standard size. |
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BHM1162020 |
RING SET, 4 piston set |
1 |
+0.020" oversize. |
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BHM1162030 |
RING SET, 4 piston set |
1 |
+0.030" oversize. |
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BHM1162040 |
RING SET, 4 piston set |
1 |
+0.040" oversize. |
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BHM1162060 |
RING SET, 4 piston set |
1 |
+0.060" oversize. |
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1098cc 1980-81 (A Plus) |
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4 Ring Piston With 0.158" Thick Special Oil Ring |
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Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
15 |
BAU4418STD |
PISTON SET, set of 4, dished piston crown |
1 |
8.5:1 compression ratio, standard size. |
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BAU4418020 |
PISTON SET, set of 4, dished piston crown |
1 |
8.5:1 compression ratio, +0.020" oversize. |
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BAU4418030 |
PISTON SET, set of 4, dished piston crown |
1 |
8.5:1 compression ratio, +0.030" oversize. |
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BAU4418040 |
PISTON SET, set of 4, dished piston crown |
1 |
8.5:1 compression ratio, +0.040" oversize. |
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BAU4418060 |
PISTON SET, set of 4, dished piston crown |
1 |
8.5:1 compression ratio, +0.060" oversize. |
16 |
BHM1465STD |
RING SET, 4 piston set |
1 |
Standard size. |
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BHM1465020 |
RING SET, 4 piston set |
1 |
+0.020" oversize. |
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BHM1465030 |
RING SET, 4 piston set |
1 |
+0.030" oversize. |
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BHM1465040 |
RING SET, 4 piston set |
1 |
+0.040" oversize. |
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BHM1465060 |
RING SET, 4 piston set |
1 |
+0.060" oversize. |
17 |
CCN210 |
CIRCLIP, gudgeon pin |
8 |
Not 998cc 1988 on. |
18 |
12G164 |
LINER, cylinder |
4 |
Standard size. |
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Connecting Rods and Crankshaft |
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Connecting Rods 1963-88 |
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(Gudgeon Pin Retained By Circlips) |
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In 1981 the connecting rod big end cap screw was changed to an improved stretch bolt design which no longer required a lock tab to ensure it was secured in place. New connecting rod assemblies are most likely to include stretch bolts, although 'new old stock' rods with bolts and lock tabs that have been gathering dust in a corner of a store for many years may still surface from time to time. When reassembling an engine, make sure all big end caps are secured by the same bolt design. |
Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
19 |
12G123 |
ROD ASS'Y, connecting, nos 2 and 4 |
2 |
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20 |
12G126 |
ROD ASS'Y, connecting, nos 1 and 3 |
2 |
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21 |
12G125 |
BUSH, small end |
4 |
Included in rod assembly. |
22 |
12G2217 |
BOLT, connecting rod cap ('big end') |
8 |
1963-81; see note above. |
23 |
2A660 |
LOCK TAB, bolt |
4 |
1963-81; see note above. |
24 |
CAM6126 |
BOLT, connecting rod cap ('big end') |
8 |
1981-88; see note above. |
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Connecting Rods 1988 On |
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(Press Fit Gudgeon Pin) |
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Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
25 |
12A1997 |
ROD ASS'Y, connecting, nos 2 and 4 |
2 |
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26 |
12A1999 |
ROD ASS'Y, connecting, nos 1 and 3 |
2 |
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27 |
12G125 |
BUSH, small end |
4 |
Included in rod assembly. |
28 |
CAM6126 |
BOLT, connecting rod cap ('big end') |
8 |
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29 |
8G2198STD |
BEARING SET, connecting rod ('big end bearings') |
1 |
Set of 4 pairs, standard size. |
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8G2198010 |
BEARING SET, connecting rod ('big end bearings') |
1 |
Set of 4 pairs, 0.010" undersize. |
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8G2198020 |
BEARING SET, connecting rod ('big end bearings') |
1 |
Set of 4 pairs, 0.020" undersize. |
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8G2198030 |
BEARING SET, connecting rod ('big end bearings') |
1 |
Set of 4 pairs, 0.030" undersize. |
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8G2198040 |
BEARING SET, connecting rod ('big end bearings') |
1 |
Set of 4 pairs, 0.040" undersize. |
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Crankshaft |
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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. |
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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 or the 'Automatic Transmission - Torque Converter and Housing' section in the Transmissions area of the Somerford Mini catalogue. |
Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
30 |
8G2733 |
CRANKSHAFT ASS'Y (with 1963-83 main bearings) |
1 |
998cc 1963-83. Stamped no. 12A595 or 12A1451. |
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BHM1436 |
CRANKSHAFT ASS'Y (with 1983 on main bearings) |
1 |
998cc 1983 on. Stamped no. 12A1451. |
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8G2732 |
CRANKSHAFT ASS'Y (with 1963-83 main bearings) |
1 |
1098cc. Stamped no. 12G82. |
31 |
12A1451 |
CRANKSHAFT, bare |
1 |
998cc. Stamped 12A1451. |
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12G82 |
CRANKSHAFT, bare |
1 |
1098cc. Stamped no. 12G82. |
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There are two distinct main bearing designs: 8G2332 bearings have locating lugs on the edge of both upper and lower halves, whereas BHM1573 bearings have lugs on the edge of the upper halves and in the centre of the lower halves. They cannot be interchanged in engines because the engine main bearing caps are unique for each design. |
Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
32 |
8G2332STD |
BEARING SET, main bearings, set of 3 pairs |
1 |
998cc 1963-83 and 1098cc; std. size. |
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8G2332010 |
BEARING SET, main bearings, set of 3 pairs |
1 |
998cc 1963-83 and 1098cc; 0.010" undersize. |
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8G2332020 |
BEARING SET, main bearings, set of 3 pairs |
1 |
998cc 1963-83 and 1098cc; 0.020" undersize. |
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8G2332030 |
BEARING SET, main bearings, set of 3 pairs |
1 |
998cc 1963-83 and 1098cc; 0.030" undersize. |
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8G2332040 |
BEARING SET, main bearings, set of 3 pairs |
1 |
998cc 1963-83 and 1098cc; 0.040" undersize. |
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BHM1573STD |
BEARING SET, main bearings, set of 3 pairs |
1 |
998cc 1983 on; std. size. |
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BHM1573010 |
BEARING SET, main bearings, set of 3 pairs |
1 |
998cc 1983 on; 0.010" undersize. |
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BHM1573020 |
BEARING SET, main bearings, set of 3 pairs |
1 |
998cc 1983 on; 0.020" undersize. |
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BHM1573030 |
BEARING SET, main bearings, set of 3 pairs |
1 |
998cc 1983 on; 0.030" undersize. |
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BHM1573040 |
BEARING SET, main bearings, set of 3 pairs |
1 |
998cc 1983 on; 0.040" undersize. |
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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 |
33 |
BHM1292STD |
THRUST WASHERS, crankshaft, pair |
A/R |
Standard size. |
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BHM1292003 |
THRUST WASHERS, crankshaft, pair |
A/R |
+0.003" oversize. |
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BHM1292030 |
THRUST WASHERS, crankshaft, pair |
A/R |
+0.030" oversize. |
34 |
6K836 |
KEY, Woodruff, crankshaft |
1 |
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35 |
8G725 |
GEAR, timing chain, crankshaft |
1 |
998cc (not Cooper) and 1098cc. |
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AEA538 |
GEAR, timing chain, crankshaft |
1 |
998cc (Cooper). |
36 |
6K628 |
WASHER, packing |
A/R |
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37 |
12A1148 |
OIL THROWER, crankshaft |
1 |
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38 |
88G561 |
OIL SEAL, timing cover |
1 |
Included in timing cover assembly. |
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Crankshaft Pulley |
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The 998cc (not Cooper) engine was not fitted with a vibration damper type pulley, whereas the 1098cc engine used a one-piece damper pulley. The 998cc Cooper unit also received one, or in fact two different ones. The original design was a separate pulley with a with a damper screwed to it; eventually a one-piece damper pulley was offered as a replacement but in fact both set ups remained available as spares for many years. If you want the original pulley, it is still available today from Somerford Mini. |
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Note that the bolt retaining the pulley to the crankshaft is specific to the type of pulley being fitted. Later 998cc and 1098cc engines from 1980 approximately onwards received pulleys with strobe timing plates attached as part of the A Plus modification programme. |
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998cc (not Cooper) Crankshaft Pulley |
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Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
39 |
2A940 |
PULLEY, crankshaft |
1 |
1963-70, dynamo fitted models. |
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12A1380 |
PULLEY, crankshaft |
1 |
1963-70, alternator fitted models. |
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CAM6323 |
PULLEY, crankshaft |
1 |
1970-80; may be used on earlier engines. |
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CAM6497 |
PULLEY, crankshaft |
1 |
1980 on; A Plus type with timing plate. |
40 |
AEA312 |
BOLT, pulley to crankshaft |
1 |
1963-87. |
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TAM2019 |
BOLT, pulley to crankshaft |
1 |
1987 on. |
41 |
12A398 |
LOCK TAB, pulley bolt |
1 |
1963-87. |
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TAM2020 |
LOCK TAB, pulley bolt |
1 |
1987 on. |
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998cc (Cooper) Crankshaft Pulley |
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Ill. No. |
Part No. |
Description |
Qty. Rqd. |
Remarks |
42 |
AEG454 |
PULLEY, crankshaft |
1 |
Separate pulley and damper fitment. |
43 |
12A367 |
DAMPER |
1 |
Separate pulley and damper fitment. |
44 |
SH605051 |
SCREW, damper to pulley |
4 |
Separate pulley and damper fitment. |
45 |
LWZ305 |
WASHER, locking |
4 |
Separate pulley and damper fitment. |
46 |
AEA312 |
BOLT, pulley to crankshaft |
1 |
Separate pulley and damper fitment. |
47 |
12A398 |
LOCK TAB, pulley bolt |
1 |
Separate pulley and damper fitment. |
48 |
88G305 |
PULLEY, crankshaft, with damper |
1 |
One-piece damper pulley fitment. |
49 |
12A283 |
BOLT, pulley to crankshaft |
1 |
One-piece damper pulley fitment. |
50 |
12A398 |
LOCK TAB, pulley bolt |
1 |
One-piece damper pulley fitment. |
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1098cc Crankshaft Pulley |
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