Mercruiser Alpha One gearcase (New SEI lower unit)

Lower unit gear housing assembly replacement from SEI Marine aftermarket parts

Last updated on 12/08/2023, 01:17:46

  • New complete lower unit gear housing assembly replacement
  • Forward bearing size: O.D 3.500
  • Heavy duty construction replaces original Mercruiser and Alpha 1 (One) and Gen 2 lower units
  • OEM 1623-8951A43
  • SEI P/N SE106 for 1970-1990 models, and P/N SE116 for 1991 and up (Alpha Gen 2 models)
  • Gear ratio: 13:21
  • See our Alpha 1 lower unit page for all lower gear case parts and components with photos
  • Tech support exploded view drawings search by part number or description here

lower unit complete

prop shaft lower

P/N SE106 Mercruiser R/MR/Alpha One Gen 1 complete lower units. For 1970 – 1990 models, serial numbers 2791957-OD469858. 13 spline vertical driveshaft, up to 300 horsepower.

$1125.96 US
$1499.96 CDN

P/N SE116 Alpha 1 Generation 2 complete lower units. For 1991 and up models with metal water pump impeller housing, serial numbers OD470000-Up. For up to 300 horsepower. Will not replace 2.00 or 2.40 ratio units.

$1199.96 US
$1599.96 CDN

Mercruiser aftermarket Alpha one and
generation 2 upper gear cases

Alpha 1 generation 2 upper gear case

P/N SEI-106-198 Mercruiser R/MR/Alpha One Gen 1 complete upper unit. For 1970 – 1990 models, 4 cylinder with 1.94 / 1.98 gear ratios with a 20-24 tooth count.

Compatible with 120 to 140 horsepower models with a 2.5 or 3.0 liter motor, 1971 to 1990, serial numbers 2791957 to 6225576.

*Note – before ordering, please measure your output shaft that goes into the engine. Replacement upper units come with an output shaft that measures 9-9/16 inch. If your shaft is the ‘short style’ which measures 8-1/8 inches, please contact us for availability.

$1049.96 US

includes u-joints and output shaft

$949.96 US

does not include u-joints and output shaft

$1399.96 CDN

includes u-joints and output shaft

$1265.96 CDN

does not include u-joints and output shaft

P/N SE106-181 Mercruiser R/MR/Alpha One Gen 1 complete upper unit. For 1976 – 1982 models with 4 cylinder 470 / 485 models and 1986 – 1990 4.3 liter V6. 1.81 / 1.84 gear ratio with a 17-19 tooth count.

Compatible with inline 4 cylinder 3.7 liter motors serial numbers 4208730 to 6225576, and 4.3 liter 185 / 190 horsepower V6 motors serial numbers 6225577 to 0D469858.

*Note – before ordering, please measure your output shaft that goes into the engine. Replacement upper units come with an output shaft that measures 9-9/16 inch. If your shaft is the ‘short style’ which measures 8-1/8 inches, please contact us for availability.

$1049.96 US

includes u-joints and output shaft

$949.96 US

does not include u-joints and output shaft

$1399.96 CDN

includes u-joints and output shaft

$1265.96 CDN

does not include u-joints and output shaft

P/N SE106-165 Mercruiser R/MR/Alpha One Gen 1 complete upper unit. For 1970 – 1977 models with 165 horsepower inline 6 cylinder, 1.65 / 1.62 gear ratio with a 24-24 tooth count.

Compatible with 165 models serial numbers 2763442 and up.

*Note – before ordering, please measure your output shaft that goes into the engine. Replacement upper units come with an output shaft that measures 9-9/16 inch. If your shaft is the ‘short style’ which measures 8-1/8 inches, please contact us for availability.

$1049.96 US

includes u-joints and output shaft

$949.96 US

does not include u-joints and output shaft

$1399.96 CDN

includes u-joints and output shaft

$1265.96 CDN

does not include u-joints and output shaft

P/N SE106-150 Mercruiser R/MR/Alpha One Gen 1 complete upper unit. For 1974 – 1990 models with 205 / 230 / 260 horsepower V8 motors, 1.47 and 1.50 gear ratio with a 20-22 tooth count.

Compatible with 888, 898, 228, 225-S, 233, 250, 260, 5.0 liter 305 and 5.7 liter 350 models serial numbers 2763442 and up.

$1049.96 US

includes u-joints and output shaft

$949.96 US

does not include u-joints and output shaft

$1399.96 CDN

includes u-joints and output shaft

$1265.96 CDN

does not include u-joints and output shaft

P/N SE116-147 Mercruiser Alpha One Gen 2 complete upper unit. For 1991 – up models with 230 / 260 horsepower V8 motors, 1.47 gear ratio with a 20-22 tooth count.

Compatible with 5.0 liter 305 and 5.7 liter 350 models serial numbers 0D470000 and up.

*Note – does not work with the 305 V8 200 horsepower model.

$1049.96 US

includes u-joints and output shaft

$949.96 US

does not include u-joints and output shaft

$1399.96 CDN

includes u-joints and output shaft

$1265.96 CDN

does not include u-joints and output shaft

P/N SE116-194 Mercruiser Alpha One Gen 2 complete upper unit. For 1991 – up models with 4 cylinder motors, 1.94 gear ratio with a 20-24 tooth count.

Compatible with 3.0L and 3.0LX models serial numbers 0D470000 and up.

$1049.96 US

includes u-joints and output shaft

$949.96 US

does not include u-joints and output shaft

$1399.96 CDN

includes u-joints and output shaft

$1265.96 CDN

does not include u-joints and output shaft

P/N SE116-181 Mercruiser Alpha One Gen 2 complete upper unit. For 1991 – up models with 4.3 liter V6 motors, 1.81 gear ratio with a 17-19 tooth count.

Compatible with 4.3L and 4.3LX models serial numbers 0D470000 and up.

$1049.96 US

includes u-joints and output shaft

$949.96 US

does not include u-joints and output shaft

$1399.96 CDN

includes u-joints and output shaft

$1265.96 CDN

does not include u-joints and output shaft

WARRANTY. All products manufactured by (“SEI”) are covered by warranty for either a period of one (1) year for upper gear cases purchased without u-joints and output shafts, or two (2) years for lower units and upper gear cases purchased with u-joints and output shafts from the date of actual purchase. A condition of qualification of these warranties is proof of purchase of the SEI product. Proof of purchase must be supplied by customer prior to warranty application and/or receiving warranty benefits. These one (1) year and two (2) year warranties against manufacturing defects in workmanship and components are the sole and exclusive warranty provided by SEI and all other warranties and potential damages are limited and excluded. These warranties commence on the shipment date of products to the customer sold by TC Electronics to the purchaser. Please see SEI limited sterndrive warranty or service information

 

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51140 Exhaust manifold elbow

P/N 51140 Mercruiser Alpha One exhaust manifold elbow/riser $143.95

Includes:
P/N 30240 Elbow/riser gasket
P/N 21892 plug
P/N 22379 plug
P/N 22381 x 4 mounting bolts

12120 water pump 46-44292A5

P/N 12120 Mercruiser Alpha One water pump kit with housing – years 1984 – 1990 Serial numbers 6854393 – OD469858 $35.95

Includes:
P/N 12322 / 46-44292A3 Pump base
P/N 89840 / 47-89984T4 Impeller
P/N 12410 / 46-96148T1 Housing
P/N 12510 / 32435 Wear plate
P/N 12820 / 23-29804T Guide tube
P/N 11070 / 28-56654 Key
P/N 12810 / 48752 Cup
P/N 31010 / 27-85608-1 Gasket

21950 Bellows kit

P/N 21950 Transom Mercruiser Alpha One bellows kit (1973-1990), serial numbers 3469428 – 0D469800. 30-803097T1 $145.95

Includes:
P/N 89100 exhaust bellow
P/N 89050 drive shaft bellow
P/N 21906 Gimbal bearing
P/N 39622 bell housing gasket
P/N 47110/47120 water hoses
P/N 89080 shift cable bellow
P/N 85910 oil seal

87511 Seal kit 26-816575A3

P/N 87511 Mercruiser Alpha One seal kit, replaces 26-816575A3 Alpha 1 Generation 2 (1991 and up) Serial numbers OD469859 – up. $35.95

12043 Impeller kit

P/N 12043 Alpha One Gen 2 impeller kit with coupling for Gen 2 Alpha 1 Generation 2 (1991 and up) Serial numbers OD469859 and up. *Does not include housing. $37.95

Included:
P/N 89630 / 47-43026T2 Impeller
P/N 12824 / 816597A1 Coupling assembly
P/N 85590 / 26-816575A2 Seal
P/N 12500 / 817276-1 Wear plate
P/N 30090 / 27-43033-1 Gasket
P/N 82110 / 25-21836 O Ring
P/N 31240 / 27-817277 Gasket

89100 Exhaust bellow 18654A1

P/N 89100 Mercruiser Alpha One exhaust bellow with hose clamps and grounding clips. Replaces 18654A1 or Sierra 18-2750 $22.95

21450 Shift cable 865436A03

P/N 21450 Mercruiser Alpha One shift cable. Updated cable with larger core wire. Compatible with 1967 – present Mercruiser and Alpha 1 and Gen 2 models. OEM 865436A03 $79.95

88010 Mercruiser rebuild kit

P/N 88010 Outdrive service kit for MC-1/R 1970 – 1983 $99.95

Parts included:
P/N 12110 Water pump impeller kit
P/N 87500 Upper housing seal kit
P/N 87510 Lower unit seal kit

88020 Alpha One rebuild kit

P/N 88020 Outdrive service kit for MR/Alpha 1 1984-1990 $99.95

Parts included:
P/N 87500 Upper housing seal kit
P/N 12120 Water pump impeller kit
P/N 87510 Lower unit seal kit

87510 Mercruiser Alpha One seal gasket kit 26-33144A2

P/N 87510 Mercruiser Alpha One outdrive seal kit for 1967-1990 (s/n 2062141 – 0D469800) $38.95

Includes:
P/N 21330 Slinger 25-30271
P/N 21010 bushing assembly 23-30617A2
P/N 85040 Oil seal 26-16977
P/N 12830 Seal 25-39970
P/N 81160 O-ring 25-30613
P/N 85070 Oil seal 26-89238
P/N 81390 O-ring 25-90011
P/N 81180 O-ring 25-25439
P/N 31020 Gasket 25-858524
P/N 31050 Gasket 27-42631-1
P/N 31010 Gasket 27-85608-1
P/N 85700 Oil seal 26-12224
P/N 85581 Oil seal 26-816464
P/N 85140 Seal 26-45577-1

87500 Seal kit 26-32511A1

P/N 87500 Alpha One upper gearcase seal kit. Replaces 26-32511A1. For M1 / R / MR / Alpha 1 (1964 – 1990) serial numbers 1684188 – OD469858 $24.95

Includes:
P/N 85150 Grommet
P/N 85020/85060/85030 Oil seals
P/N 80420 O-ring P/N 80190 O-ring
P/N 81180 O-ring P/N 82380 O-ring
P/N 31150 Gasket

39622 Mercruiser Alpha One bell housing gasket 27-94996T2

P/N 39622 Mercruiser bell housing gasket set (1983 and up, s/n 6225577 – up). For R / MR / Alpha 1 and Gen 2. $9.95

12110 Mercruiser Water pump kit 46-57234A3

P/N 12110 Mercruiser water pump kit with housing. For years 1970 – 1983 Serial numbers 2763442 – 6854392 $39.95

Includes:
P/N 12410 / 46-96148T1 Pump housing
P/N 89840 / 47-89984T4 Impeller
P/N 12820 / 23-29804T Guide tube
P/N 11070 / 28-56654 Key
P/N 12310 / 46-57234T1 Pump base
P/N 12810 / 48752 Cup
P/N 12510 / 32435 Wear plate
P/N 31010 / 27-85608-1 Gasket