MerCruiser Alpha One Gen I complete standard-rotation sterndrive

Alpha OneĀ® Gen II Sterndrive Lower Applications

Shop Alpha One Gen II lower unit replacements for MerCruiser sterndrives, including standard SE116, high-altitude SE116-HA, and counter-rotation gearcase applications. Verify your existing drive configuration before ordering.

Alpha OneĀ® Gen II Sterndrive Lower Applications

Shop MerCruiser Alpha One Gen II lower-only gearcases (1991-present) ā€” replacement lower units for boaters who already have a serviceable upper gear case and only need the lower section replaced due to wear, corrosion, or impact damage.

Pair this Alpha One Gen II lower unit with your existing upper section for a cost-effective partial rebuild.

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  • Lower Unit | SE116 | Mercruiser Alpha One Gen II 1991+

    Lower Unit | SE116 | Mercruiser Alpha One Gen II 1991+ SKU: SE90-116-02
    MPN: 90-116-02

    $1,065.00
    $1,182.15
    $1,065.00
    Restore your driveā€™s reliability and propulsion efficiency with this Standard Rotation Lower Unit, a premium aftermarket replacement for Mercruiser Alpha One Gen II stern drives. Engineered to meet or exceed OEM standards, this unit features a heavy-duty housing and precision-machined internal gears designed for...
    $1,065.00
    $1,182.15
    $1,065.00
  • Lower Unit | SE116-HA | Mercruiser Alpha One Gen II

    Lower Unit | SE116-HA | Mercruiser Alpha One Gen II SKU: SE90-116-02H
    MPN: 90-116-02HA

    $1,065.00
    $1,182.15
    $1,065.00
    Restore your drive's reliability with this High-Altitude (HA) Lower Unit, a premium aftermarket replacement engineered specifically for Mercruiser Alpha One Gen II stern drives. Designed for precision power transmission, this unit features a heavy-duty housing and corrosion-resistant internals built to withstand demanding marine environments....
    $1,065.00
    $1,182.15
    $1,065.00
  • Counter Rotating Lower Unit | SE116 | Mercruiser Alpha One Gen II

    Counter Rotating Lower Unit | SE116 | Mercruiser Alpha One Gen II SKU: SE90-118-02
    MPN: 90-118-02

    $1,295.00
    $1,437.45
    $1,295.00
    Restore precision handling and smooth power delivery with this Counter Rotating Lower Unit, a premium aftermarket replacement for Mercruiser Alpha One Gen II stern drives. Engineered for high-torque applications up to 300HP, this unit features a heavy-duty housing and precision-cut internal gears designed to...
    $1,295.00
    $1,437.45
    $1,295.00

A Clearer Way to Select Your Replacement Drive

Compare the configuration details that matter before choosing a sterndrive.

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Coverage on select lower units

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How to Choose the Correct Alpha One Gen II Lower Unit

Choosing the correct Alpha One Gen II lower unit starts with identifying the drive you already have. Even when two gearcases look similar externally, the correct replacement can depend on the drive generation, overall gear ratio, upper-drive configuration and propeller rotation.

Before purchasing a MerCruiser Alpha One Gen II replacement lower unit, collect as much identification information as possible from your existing drive. If the original configuration has been changed in the past, do not rely on engine size or model year alone.

Verify These Details Before Ordering:

  • Record the engine model and serial number
  • Record the sterndrive serial number
  • Check the existing overall drive ratio
  • Identify the existing lower-unit part number
  • Verify standard or counter rotation
  • Determine whether the setup uses a standard or SE116-HA lower
  • Send photos of drive labels or identification markings if anything is unclear

Alpha One Gen II Gear Ratio & Lower Unit Guide

The overall Alpha One Gen II drive ratio is created by the upper and lower gear combination. When replacing only the lower unit, verify the existing ratio and matching upper-drive configuration rather than assuming that every Gen II lower will interchange.

Overall Drive Configuration Lower-Unit Selection
1.47 Standard ā€” SE116 / 90-116-02 ā€” Verify existing upper and complete-drive configuration
1.62 Standard ā€” SE116 / 90-116-02 ā€” Confirm current ratio before replacing only the lower
1.81 Standard ā€” SE116 / 90-116-02 ā€” Match existing Alpha One Gen II configuration
1.94 Standard ā€” SE116 / 90-116-02 ā€” Verify existing drive ratio and identification before ordering
2.00 High Altitude / HA ā€” SE116-HA / 90-116-02H ā€” Do not substitute the standard lower without verification
2.40 High Altitude / HA ā€” SE116-HA / 90-116-02H ā€” Used for the specific 2.40 drive configuration

Lower Unit, Upper Unit or Complete Sterndrive?

Before ordering, determine which portion of your Alpha One Gen II sterndrive actually needs replacement. A lower unit solves a different repair need than an upper unit or complete sterndrive assembly.

Lower Unit

  • Choose an Alpha One Gen II lower unit when the required replacement is limited to the lower gearcase
  • Ensure the retained upper unit is confirmed to be serviceable and compatible

Upper Unit

  • Choose an Alpha One Gen II upper unit when the repair is isolated to the upper drive assembly
  • Ensure the existing lower unit remains suitable for the required configuration

Complete Sterndrive

  • Choose a complete Alpha One Gen II sterndrive when replacing both the upper and lower assemblies
  • Choose a complete Alpha One Gen II sterndrive when the condition of the existing drive makes a complete replacement the more appropriate path
An informational comparison graphic titled 'STANDARD VS COUNTER ROTATION' showing two outboard motors and two propellers, with text explaining the difference in propeller direction when viewed from behind. The background is a real marina scene with water and boats, but the image functions as an explanatory diagram rather than a straightforward product photo.

Standard vs Counter-Rotation Alpha One Gen II Lower Units

Propeller rotation is another critical selection point when replacing an Alpha One Gen II lower unit. Standard and counter-rotation gearcases are different applications and should be identified from the existing drive before ordering.

Standard Rotation

Choose the SE116 standard lower-unit path when your existing Alpha One Gen II drive uses the compatible standard-rotation configuration.

Counter Rotation

Choose the counter-rotating SE116 lower unit only when the existing Alpha One Gen II drive is configured for counter rotation. Counter-rotation gearcases are commonly encountered in specific multi-drive applications, but boat position alone should not be used as proof of rotation.

Shop Alpha One Gen II Lower Units by Gear Ratio

Use your existing Alpha One Gen II gear ratio as a starting point when selecting a replacement lower unit. Standard SE116 and SE116-HA lower units serve different drive configurations, so confirm the complete upper-and-lower setup before ordering.

  1. 1.47 Alpha One Gen II

    Shopping for an Alpha One Gen II 1.47 lower unit? Compatible 1.47 drive configurations use the standard SE116 lower-unit replacement path. Verify your existing drive identification and rotation before ordering.

    Shop 1.47 Lower Unit

  2. 1.62 Alpha One Gen II

    For a compatible Alpha One Gen II 1.62 drive configuration, start with the standard SE116 lower unit. Confirm the existing upper-drive ratio, lower configuration and rotation before purchasing.

    Shop 1.62 Lower Unit

  3. 1.81 Alpha One Gen II

    The Alpha One Gen II 1.81 lower-unit shopping path uses the standard SE116 replacement for compatible configurations. Match your current drive information rather than selecting by ratio alone.

    Shop 1.81 Lower Unit

  4. 1.94 Alpha One Gen II

    Compatible Alpha One Gen II 1.94 applications use the standard SE116 lower-unit replacement path. Verify your current drive ratio, identification and propeller rotation before ordering the gearcase.

    Shop 1.94 Lower Unit

  5. 2.00 Alpha One Gen II

    Alpha One Gen II 2.00 drive configurations require special attention when replacing only the lower unit. The applicable shopping path is the SE116-HA lower unit rather than the standard SE116.

    Shop 2.00 Lower Unit

Replacement Lower Units for MerCruiser Alpha One Gen II

A damaged or worn gearcase does not always require replacement of the entire sterndrive. For boats equipped with a compatible MerCruiser Alpha One Gen II drive, replacing only the lower assembly can provide a focused repair path when the existing upper remains serviceable.

This collection includes aftermarket Alpha One Gen II lower-unit options for standard SE116, SE116-HA high-altitude, and counter-rotation applications. Because these configurations are designed for different upper/lower combinations and rotation requirements, correct identification is essential. Compare your existing part number, overall gear ratio, rotation and sterndrive information before selecting a replacement.

What Customers Say

Direct replacement lower gearcase for 1998 Alpha Gen II

Replaced a damaged lower unit on my 1998 4.3L Mercruiser. The SE116 lower assembly bolted up directly to my upper gearcase without alignment issues. Having the pre-installed water pump impeller made the job much faster.
Gregory Vance Verified buyer
August 2026

Smooth shifting and reliable water pump flow

The product details on Mariners Warehouse made it easy to verify that this lower unit fits all Gen II models from 1991 to present. Shift linkage aligned properly right out of the box, and water pressure stays steady at high RPMs.
Eliana Frost Verified buyer
July 2026

Great fit for 2003 5.0L MPI standard rotation

Ordered this standard rotation Gen II lower gearcase to replace a cracked housing. The drive shaft splines matched the upper unit perfectly. Be sure to replace the quad ring seal between the upper and lower during installation.
Simon Sterling Verified buyer
June 2026

Clear fitment guidance for Gen I vs Gen II lower

I was unsure if my 1994 setup took a Gen I or Gen II lower unit, but the listing clearly highlighted the internal water pump design unique to Gen II. Fitment support confirmed my model specs before shipping.
Natalie Ross Verified buyer
May 2026

Securely packaged with new anode kit included

The lower unit arrived double-boxed with foam inserts to prevent shipping damage. Driveshaft and prop shaft came well-greased and ready. It eliminated the lower gear whine on my 5.7L bowrider.
Julian Hayes Verified buyer
April 2026

Flawless mate with existing Gen II upper unit

Installed this replacement lower on my 2001 3.0L Alpha One setup. The studs aligned easily with the upper housing. Shifting into forward and reverse is crisp with no hesitation.
Camila Thorne Verified buyer
March 2026

Solid build quality for twin 350 Mag port side

Purchased the counter-rotating lower gearcase configuration for our port engine. The propshaft, seals, and paint finish matched OEM quality. Remember to follow the proper 10-hour gear lube break-in period.
Dominic Wright Verified buyer
February 2026

Saved thousands compared to OEM Mercruiser lower

Replaced my unit after striking a submerged log. The fitment instructions on Mariners Warehouse made ordering simple, and the drive has performed flawlessly through its first 20 hours on the water.
Audrey Miller Verified buyer
January 2026

Helpful Guides

Use these guides to identify your MerCruiser drive, understand gear-ratio selection and decide whether you need a complete sterndrive, upper unit or lower unit.

Marine technician holding an Alpha One Gen II lower unit gearcase next to the drive housing to check fitment details

How to Choose an Alpha One Gen II Lower Unit: SE116 Fitment Guide

How to Choose an Alpha One Gen II Lower Unit: SE116 Fitment Guide A lower unit replacement only fits correctly...

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Two Alpha One Gen II lower unit gearcases labeled standard and high altitude configuration side by side on a workshop bench

SE116 vs SE116-HA: Which Alpha One Gen II Lower Unit Fits?

SE116 vs SE116-HA: Which Alpha One Gen II Lower Unit Fits? Comparing SE116 vs SE116 HA is one of the...

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Standard and counter-rotating Alpha One Gen II lower unit gearcases side by side on a workshop bench for comparison

Alpha One Gen II Standard vs Counter-Rotation Lower Units?

Alpha One Gen II Standard vs Counter-Rotation Lower Units Standard and Alpha One Gen II counter rotation lower units may...

Read More ā†’

Frequently Asked Questions

How do I know which Alpha One Gen II lower unit I need?

Start by confirming that your sterndrive is an Alpha One Gen II, then identify the existing overall gear ratio, propeller rotation and lower-unit or gearcase part number. Standard SE116, SE116-HA and counter-rotation lower units serve different configurations, so do not select a replacement by appearance alone.

What is the difference between the SE116 and SE116-HA lower units?

The standard SE116 and SE116-HA are intended for different Alpha One Gen II drive configurations. The SE116-HA 90-116-02H is used for specific 2.00 and 2.40 configurations, while the standard 90-116-02 serves the standard lower-unit application group.

Which lower unit is used with a 2.00 Alpha One Gen II drive?

A 2.00 Alpha One Gen II drive can require the SE116-HA 90-116-02H lower-unit configuration. Because the overall ratio depends on the upper and lower combination, verify the existing drive before replacing only the lower unit.

Which lower unit is used with a 2.40 Alpha One Gen II drive?

The SE116-HA 90-116-02H is the replacement path associated with the 2.40 Alpha One Gen II drive configuration. Confirm that your existing drive is actually configured as 2.40 before ordering.

Can I use a standard SE116 lower unit instead of an SE116-HA?

Not when the existing drive requires the HA lower configuration. The standard and high-altitude lower units use different gearing, so the existing upper/lower combination must be verified before substituting either assembly.

What is an Alpha One Gen II counter-rotation lower unit?

A counter-rotation lower unit is designed for an Alpha One Gen II drive configured to turn the propeller in the counter-rotating direction. The SE116 counter-rotation replacement listed in this collection is 90-118-02.

Can I determine rotation by which side of the boat the drive is on?

Do not rely on drive position alone to identify rotation. Confirm the existing gearcase, part number and propeller rotation before choosing a standard or counter-rotation Alpha One Gen II lower unit.

Will an Alpha One Gen II lower unit fit an Alpha One Gen I drive?

Do not assume Gen I and Gen II lower units are interchangeable. This collection is specifically intended for compatible Alpha One Gen II applications, so confirm your sterndrive generation before ordering.

Should I replace the lower unit or the complete Alpha One Gen II sterndrive?

A lower-unit replacement may be appropriate when the repair is isolated to the gearcase and the existing upper assembly is still serviceable and compatible. If both major assemblies are damaged or their compatibility cannot be confirmed, compare the complete sterndrive replacement path.

What information should I send for Alpha One Gen II lower-unit fitment help?

Send the engine model and serial number, sterndrive serial number, existing gearcase part number, overall drive ratio, rotation and clear photos of available identification labels. The more information available, the easier it is to narrow down the correct Alpha One Gen II replacement lower unit.

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