Mercruiser Alpha 1 Gen 2 lower unit parts drawing

Alpha One lower unit gearcase

Updated April 18th 2026

• MerCruiser and Alpha One up to 1990
• Lower unit parts drawing
• Water pump components, seals, shafts and gear sets
• Manufactured by GLM, California.
• Easy to identify photos with OEM Mercury numbers

Mercruiser Alpha 1 Gen 2 lower unit

Upper Housing

Description
OEM number

Price
(USD)

Price (Canadian)

SEI Mercruiser Alpha 1 Gen 2 lower unit

Item 1
SEI-SE116

SEI lower unit Mercruiser Alpha One Gen 2 lower unit. Years 1991 and up models only.

Serial numbers OD470000 and up.

4 cyl., V6 and V8 models up to 300 horse power. Will not replace 2.00 or 2.40 ratio units.

$1499.99

$2149.99

85590 Face seal

#2

Face seal

26 – 816575 A2

$4.95

$6.89

89630 Mercruiser water pump impeller

#3

Impeller

47 – 43026T2

$15.95

$26.89

31240 Gasket

#4

Gasket

27 – 817277 – 1

$4.95

$4.89

12500 Face plate

#5

Face plate

817276 – 1

$6.95

$10.89

30090 Gasket

#6

Gasket

27 – 43033 – 1

$4.95

$4.89

81390 O-ring

#7

O ring

25 – 90011

$4.95

$4.89

85011 Oil seal

#8

Oil seal

26 – 66302

$8.95

$11.89

23200 Mercruiser Retainer

#9

Retainer

824519 – 1

$4.95

$6.89

21580 Roller bearing

#10

Roller bearing

Years 1991 to 1997

31 – 36387 A1

$40.95

$ 66.89

21584 Roller bearing

#10

Roller bearing

(1998 & up)

31 – 33138 A1

$41.95

$ 57.89

23210 Shim

#11

Shim

15 – 42637 A1

$16.95

$37.89

11140 Drive shaft

#12

Drive shaft

45 – 816919

$529.95

$700.89

85581 Oil seal

#13

Oil seal

26 – 816464 – 1

$7.95

$13.89

81175 O-ring

#14

O ring

25 – 896522

$4.95

$4.89

85140 Seal

#15

Seal

26 – 45577 – 1

( 5 pack )

$9.99

$12.99

31170 Gasket

#16

Gasket

12 – 19183 – 3

( 5 pack )

$10.99

$14.99

21731 Draining Screw

#17

Screw

22 – 8M 0058389

$4.95

$7.89

21610 Pinion bearing

#18

Roller bearing

31 – 42647A1

$35.95

$46.89

11091 Alpha 1 Gen 2 Forward gear set

#19

Forward gear set

Years 1991 to 1995

$ 528.89

$629.95

11092 Alpha1 Gen2 Forward gear set

#19

Forward gear set

Years 1996 and up

43 – 878087 A2

$ 573.89

$686.95

32800 Washer

#20

32800

Washer

$4.95

$4.89

11190 Pinion nut

#21

Pinion nut

11 – 35921

$4.95

$5.89

12710 Trim tab anode

#22 

Trim tab anode

76214 Q5

$16.95

$27.89

11040 Shift crank

#23

Shift crank

76865

$67.95

$111.89

11030 Mercruiser Alpha 1 Gen 2 Shift spool

#24

Shift spool

818349 T1

$86.95

$141.89

23220 Mercruiser Shim

#25 Shim

Years 1991 to 1995

3.500 O.D.

15 – 47397 A1

$11.95

$ 23.89

23221 Alpha 1 Gen 2 Shim

#25

Shim

1996 and up

 3.265 O.D.

15 – 44491 A1

$5.95

$ 9.89

21590 Bearing

#26

Bearing

1.875 I.D.
3.500 O.D.

31 – 35928 T1

$59.95

$82.89

21591 Mercruiser Bearing

#26

Bearing

1.750 I.D.
3.500 O.D.

31 – 828437 A2

$67.89

$115.95

21593 Bearing

#26 

Bearing

1.875 I.D.

3.265 O.D.

31 – 828439 A2

$128.95

$176.89

21820 Bearing

#26

Bearing

1.750 I.D.

3.265 O.D.

31 – 30894 A1

$35.95

$61.89

11420 Roller bearing

#27

Roller bearing

31 – 30895 T

$14.95

$24.89

11050 Spring

#28

Spring

24 – 30893

$4.95

$4.89

21131 Cross pin

#29

Cross pin

17 – 8M 0020941

$4.95

$6.89

11060 Clutch

#30

Clutch

52 – 853594 T

$225.95

$297.89

11155 Alpha 1 Gen 2 Prop shaft

#31

Prop shaft

43 – 850308

$630.89

$660.95

11013 Mercruiser Reverse gear

#32

Mercruiser Reverse gear

43 – 828073 A1

$ 154.89

$250.95

23140 Thrust ring

#33

Thrust ring

68100 – 1

$11.95

$15.89

21620 Ball bearing

#34

Ball bearing

30 – 88957 T

$37.95

$56.89

83445 O-ring

#35

O-ring

25 – 896524

$4.95

$4.89

11410 Roller bearing

#36

Roller bearing

31 – 30956 T

$9.95

$12.89

85130 Oil seal

#37

Oil seal

26 – 14077

$7.95

$ 13.89

85700 Oil seal

#38

Oil seal

26 – 12224

$12.95