OMC Parts Drawing *Cobra *Mercruiser *Alpha SEI Outdrives
- SEI upper / lower unit Alpha outdrive
New aftermarket SEI outdrive replacement lower stern drives
for 4 cylinder, V6 and V8 engines
Updated April 17th 2026
- Sterndrive engineering aftermarket replacement lower gearcase comes with full 3 year fault-free warranty on SEI replacement sterndrives
- Replacement sterndrives and parts compatible with years 1970 to present models
- SEI aftermarket Mercruiser, MR, Alpha one and gen ii lower units and replacement upper units. All gear ratios available for all motors, 4 cylinder, V6 and V8 on Mercruiser Alpha one and gen ii lower units
- No core charge required on new lower/upper gearcases
- New Johnson/Evinrude replacement outboard lower units
Mercruiser -Alpha one lower unit 1970 to 1990
Replacement sterndrives
Description OEM number
Price
(USD)
Price (Canadian)
SEI Mercruiser lower unit 1623 - 8951 A43
SEI 106 stern drive
P/N SE106
New aftermarket SEI Marine replacement lower unit gear case, replaces Mercruiser lower units up to 1990.
Lower units compatible with 1.94, 1.98, 1.81, 1.65 and 1.50 gear ratios, 4 cylinder, 6 cylinder and V8 motors, up to 300 hp.
SEI lower units have a three year warranty on stern drives.
Note anode is not included with replacement lower unit purchase.
Years 1970 to 1990, Models Mercruiser 1, R MR and Alpha One with serial numbers
2791957 – OD 469858
Mercruiser Alpha one replacement lower unit has spline count of 13 on the driveshaft, the pinion tooth count of 13 and drive or reverse gear of 21 teeth.
OEM number
1623 – 8951 A43
$1399.99 US
$1999.99 CDN
Alpha one Gen II lower unit 1991 and up
SEI Marine aftermarket outdrive
Prop shaft bearing carrier
- Alpha one Gen ii replacement lower unit.
- For 1991 and up replacement lower unit with metal water pump impeller housing, serial numbers OD 470000 Up.
- Up to 300 horsepower. Will not replace 2.00 or 2.40 ratio units.
$1499.99 US
$2149.99 CDN
Mercruiser / Alpha One 1970-1990 Upper Gear Cases
SEI Marine aftermarket outdrive
Description / OEM #
Price
(USD)
Price (Canadian)
OEM numbers
1547 – 9412 A20,
1547 – 9412 A21,
1547 – 9412 A22,
1547 – 9412 A23,
1547 – 9412 A19
6 Cyl. 165 hp.
P/N SEI 106 – 1.65
SEI Marine aftermarket Mercruiser replacement upper unit.
Compatible with 1970 – 1977 models, 165 horsepower inline 6 cylinder motors, 1.65 / 1.62 gear ratio with a 24-24 tooth count.
Compatible with 165 models serial numbers 2763442 and up.
*Note please measure your output shaft that goes into the engine.
Replacement upper units come with an output shaft that measures 9-9/16 inch.
Short is the style’ which measures 8-1/8 inches, please contact us for availability.
$1249.99 US includes u-joints and output shaft
$1799.99 CDN includes u-joints and output shaft
4 cylinder 120 140 chevy
P/N SEI 106 – 1.98
Mercruiser and Alpha One aftermarket replacement upper unit.
SEI marine upper gearcase compatible with years 1970 to 1990 models, 4 cylinder engines with 1.94 / 1.98 gear ratios with a 20-24 tooth count.
Works with 120 to 140 horse power models with a 2.5 or 3.0 liter motor, 1971 to 1990, serial numbers 2791957 to 6225576.
*Note measure your output shaft that goes into the engine.
Replacement upper units come with an output shaft that measures 9-9/16 inch.
Old shaft is 8-1/8 inches, contact us for availability.
$1249.99 US includes u-joints and output shaft
$1799.99 CDN includes u-joints and output shaft
SEI marine 470 model V6 185 horsepower 17-19 ratio
P/N SEI 106 – 1.81
Mercruiser R/MR/Alpha One 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 horse power V6 motors serial numbers 6225577 to 0D 469858.
Replacement upper units come with an output shaft that measures 9-9/16 inch.
Short style’ which measures 8-1/8 inches, please contact us for availability.
$1249.99 US includes u-joints and output shaft
$1799.99 CDN includes u-joints and output shaft
1974 - 1990 models
SEI 106 1.50 and 1.47 ratio
Mercruiser and Alpha One Gen 1 replacement upper unit.
For 1974 to 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.
$1249.99 US includes u-joints and output shaft
$1799.99 CDN includes u-joints and output shaft
Mercruiser Alpha One Gen 2 1991-Up Upper Gear Cases
4 cylinder 3 litre engine
Alpha 1 Gen 2 aftermarket replacement upper unit for years 1991 and up.
Models with 4 cylinder motors, 1.94 gear ratio with a 20-24 tooth count.
Compatible with 3.0 liter and 3.0 LX models serial numbers 0D469859 – 0K999999.
*Note – Will NOT work for 1998 and newer models with the 3.0L 4 cyl. with serial numbers OL000040-Up. For those newer models and serial numbers use the 24-24 tooth count 2.0 ratio upper unit.
Upper Gear Housing Sterndrive OEM numbers
1547 – 861063 A6
1547 – 861063 A12
1547 – 861063 A10
1547 – 861063 A8
$1249.99 US includes u-joints and output shaft
$1799.99 CDN includes u-joints and output shaft
1991 and up models with 230 / 260
Mercruiser Alpha 1 Gen ii aftermarket replacement upper unit.
For years 1991 and 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 0D 470000 and up.
Stern drives have 2 year fault free warranty
*Note – does not work with the 305 V8 200 horse power model.
$1249.99 US includes u-joints and output shaft
$1799.99 CDN includes u-joints and output shaft
BP SE116 V6 Chevy motor 17-19 ratio
Mercruiser Alpha 1 Generation 2 replacement upper unit.
For 1991 – up models with 4.3 liter V6 motors, 1.81 gear ratio with a 17-19 tooth count.
Works with 4.3L and 4.3LX models serial numbers
0D 470000 and up.
$1249.99 US includes u-joints and output shaft
$1799.99 CDN includes u-joints and output shaft
Sterndrive Installation Hardware Parts
SEI now have Mercury Johnson/Evinrude outboard lower units for sale.
Contact order desk and ask about free shipping in Canada
Alpha Gen 2 sterndrive installation parts
P/N 90 106 03K
SEI 106
Mercruiser / Alpha One Gen 1 outdrive installation parts
Includes:
- bell housing lock nuts
- washers
- mounting gasket
- intermediate shift shaft
- water pump plastic water passage tube
- stern drive lock nuts
$99.96
US
$131.89 CDN
Gen 1 installation parts
P/N 90 – 116 – 03K
SEI 106 Alpha 1 Gen 2 outdrive hardware installation parts
Includes stern drive parts:
- bolts with lock nuts
- stern drive washers
- mounting gasket
- bell housing lock nuts
- water pump plastic water passage tube
$80.96
US
$104.89 CDN
People who purchased the above also purchased the following:
Photo
Description / OEM #
Price
(USD)
Price (Canadian)
508235 OMC Johnson Compound - 4 OZ
P/N 508235 Gasket sealing compound – 4 FL. OZ (118 ml). Sealant is used on the o-rings and gaskets.
$29.95
$38.89
Please note warranty provided by SEI
WARRANTY. All products manufactured by SEI are covered by warranty for either a period of one year. Upper gear cases purchased with out u joints and output shafts.
Two years for lower units and upper gear cases purchased with u joints and output shafts from the date of actual purchase.
Qualification of warranties is proof of purchase of the SEI product. Proof of purchase by customer.
These one (1) year and three 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 Boatparts.ca to the purchaser.
In the event of a warranty claim, all warranty issues must go directly through SEI, Florida. For more information, see SEI marine sterndrive warranty or limited service or warranty information tel (813) 925-7127 warranty@sterndrive.cc