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OMC Parts Drawing *Cobra *Mercruiser *Alpha SEI Outdrives

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  • Mercruiser Alpha One lower unit parts drawing

Lower gear case housing component drawing 1 - 25

Updated April 26 2026

  • Mercruiser and Alpha One (up to 1990) lower unit drawing
  • Water pump components, seals and shafts
  • Manufactured by GLM, and SEI Marine .
  • Easy to identify photos with OEM Mercury numbers
Mercruiser outdrive parts drawing 51-77, Mercruiser Alpha One lower unit parts, Mercruiser outdrive components #26-50

Photo

Description / OEM #

Price
(USD)

Price (Canadian)

Mercruiser Alpha One lower unit parts

12110 Water pump

Item A
P/N 12120 Complete water pump kit (1984 – 1990, MR and Alpha One, serial numbers 6854393-OD469858). Click on picture for older MC-1, R and 1991 and up Gen 2 models.

$42.99

$ 63.89

Mercruiser Alpha One lower unit parts

51220 GM manifold

Item B
P/N 51220 GM 4.3L V6 exhaust manifold, center rise for 1986 and up models. Click on photo for all other engines.

99746 A17

$397.99

$556.99

Mercruiser Alpha One lower unit parts

SEI Marine Mercruiser

Lower Unit 1623 - 8951 A43

Item C
SE106

Aftermarket SEI lower unit Mercruiser / Alpha One Gen 1 complete lower units.

Years 1970 to 1990 models

Serial numbers 2791957 – OD469858 with 13 spline drive shaft, for up to 300 horse power.

OEM 1623 – 8951 A43

$1229.99

$1799.99

Mercruiser Alpha One lower unit parts

12410 Housing

Item 1

12410

Upper water pump housing

Years 1966 to 1990

#46 – 96148T1

$29.00

$ 54.89

12810 Pump cup

Item 2

12810

Pump cup

Included in upper housing and in P/N 12110 and 12120

#48752

$5.00

$ 8.89

Mercruiser Alpha One lower unit parts, 89840 Impeller for 1983-1990

89840 Impeller

Item 3

89840

Impeller

Years 1966 to 1990

#47 – 89984T4

$15.00

$ 24.89

21720

12 – 36001

$4.00

$4.89

12821 Screw OEM 10-30720

Item 5

12821

Screw

12 – 36001

$4.00

$ $ 6.89

21180

11 – 35888

$7.00

$4.89

12830 Seal

Item 7

12830

 Seal

26 – 38970

$4.00

$4.89

12820 Tube guide

Item 8

12820

Tube guide

23 – 29804T

$4.00

$ $ 6.89

81160 O-ring

25 – 30613 

$4.00

$4.89

21190 Lock nuts

Item 10

21190 

Nut (5 units)

 

$9.00

$4.89

21490 Washers

Item 11

21490

 Washer (5 units)

12 – 29245

$6.00

$4.89

11070 water pump impeller key.

11070 Key

Item 12

11070

Key

28 – 56654

$4.00

$4.89

31020 Gasket

Item 13

31020

Gasket

27 –  858524

$4.00

$4.89

Mercruiser Alpha One lower unit parts

12510 Wear plate

Item 14

12510

Wear plate

32435 – 1

$4.00

$ 6.89

31010

Item 15

31010 

Gasket

27 – 85608 – 1

$4.00

$4.89

Mercruiser Alpha One lower unit parts

12310 Base

Item 16

12310

Water pump base (1970 – 1983 only)

46  – 57234A1

$25.00

$ 44.89

oil seal

85040 Oil seal

Item 17

85040

Oil seal

26 – 16977

$8.00

$ 16.89

oil seal

85070 Oil seal

Item 18

85070

Oil seal

26 – 89238

$9.00

$ 19.89

Mercruiser Alpha One lower unit parts

82260 O ring 25-33145

Item 19

82260

O-ring (5 units)

25 – 33145

$7.00

$4.89

31040

31040

Item 20

31040

Gasket

27 – 856704

$4.00

$4.89

Mercruiser Alpha One lower unit parts

21570 Roller bearing

Item 21A

21570

Bearing

Years 1970 to 1983 only

31 – 53079A1

$23.00

$ 39.89

Mercruiser Alpha One lower unit parts

21580

Item 21B

21580

Bearing

Years 1984 to 1997 only

31 – 36387A1

$32.00

$ 66.89

23300

23300 Shims

Item 22

 23300

Shims

15 – 57007A1

$6.00

$ 10.89

21800

21800

Item 23

21800 

Washers (5 units)

12 – 29395

$5.00

$4.89

Mercruiser Alpha One lower unit parts

30010

Item 24

30010

Washers (5 units)

12 – 31266

$4.00

$4.89

85581

85581 Oil seal

Item 25

85581

Oil seal

26 – 816464 – 1

$7.00

$ 13.89

Numbers 26-50