MerCruiser Alpha One Gen I complete standard-rotation sterndrive

MERCRUISER-COMPATIBLE COMPLETE DRIVES

Alpha OneĀ® Gen I Sterndrive Applications; Counter Rotation

Shop complete aftermarket Alpha One Gen I counter-rotation sterndrives in 1.47, 1.62, 1.81 and 1.94 ratios, with selected short-yoke and regular/new-style input-yoke configurations. Verify fitment before ordering.

Alpha OneĀ® Gen I Sterndrive Applications; Counter Rotation

Shop MerCruiser Alpha One Gen I counter-rotation lower units and complete sterndrives, purpose-built for twin-engine port-side installations (1972-1990). Counter-rotation gearcases spin opposite to standard rotation to cancel out prop torque steer in dual-engine boats.

Find the correct counter-rotation Alpha One Gen I sterndrive for your port-side engine below.

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  • Alpha One Gen I Complete Drive | 1.47 Ratio | Counter Rotation

    Alpha One Gen I Complete Drive | 1.47 Ratio | Counter Rotation SKU: SE90-106-01D,90-108-02
    MPN: SE108COMPLETE-D

    $2,165.00
    $2,403.15
    $2,165.00
    Restore high-speed propulsion and balanced handling with this Complete Counter Rotation Sterndrive engineered for 1.47 Gear Ratio configurations. Designed as a Premium Aftermarket Replacement for Alpha One Gen I systems, this unit features the 9-9/16" New Style Input Yoke to ensure seamless power delivery...
    $2,165.00
    $2,403.15
    $2,165.00
  • Alpha One Gen I Complete Sterndrive | 1.62 Ratio | Counter Rotation

    Alpha One Gen I Complete Sterndrive | 1.62 Ratio | Counter Rotation SKU: SE90-106-01C,90-108-02
    MPN: SE108COMPLETE-C

    $2,165.00
    $2,403.15
    $2,165.00
    Upgrade your drivetrain with this Complete Counter Rotation Sterndrive precision-engineered for 1.62 Gear Ratio configurations. Designed as a Premium Aftermarket Replacement for Alpha One Gen I systems, this unit features a 9-9/16" New Style Input Yoke to ensure seamless power delivery and reduced vibration....
    $2,165.00
    $2,403.15
    $2,165.00
  • Alpha One Gen I Complete Sterndrive | 1.81 Ratio | Counter Rotation

    Alpha One Gen I Complete Sterndrive | 1.81 Ratio | Counter Rotation SKU: SE90-106-01B,90-108-02
    MPN: SE108COMPLETE-B

    $2,165.00
    $2,403.15
    $2,165.00
    Restore your drivetrain's peak efficiency with this Complete Counter Rotation Sterndrive engineered for 1.81 Gear Ratio configurations. Specifically designed as a direct replacement for Alpha One Gen I units, this assembly features a 9-9/16" New Style Input Yoke to ensure a precise fit and...
    $2,165.00
    $2,403.15
    $2,165.00
  • Alpha One Gen I Complete Upper & Lower | 1.94 Ratio | Counter Rotation

    Alpha One Gen I Complete Upper & Lower | 1.94 Ratio | Counter Rotation SKU: SE90-106-01A,90-108-02
    MPN: SE108COMPLETE-A

    $2,165.00
    $2,403.15
    $2,165.00
    Restore precision handling and drivetrain reliability with this Complete Counter Rotation Sterndrive engineered for 1.94 Gear Ratio applications. This premium aftermarket replacement is designed specifically for Alpha One Gen I systems, providing a durable, cost-effective solution to replace aging or damaged units. Built with...
    $2,165.00
    $2,403.15
    $2,165.00
  • Complete Sterndrive | SE104 | 1.62 Ratio | Counter Rotation

    Complete Sterndrive | SE104 | 1.62 Ratio | Counter Rotation SKU: SE90-104-01C,90-108-02
    MPN: SE106COMPLETE-SYC

    $2,165.00
    $2,403.15
    $2,165.00
    Restore balanced handling and eliminate steering torque with this Complete Counter-Rotating Sterndrive, a premium aftermarket replacement for Alpha One Gen I style drives. Engineered with a 1.62 gear ratio, this unit is optimized for high-horsepower V8 and high-output V6 engines, providing smooth power transmission...
    $2,165.00
    $2,403.15
    $2,165.00
  • Complete Sterndrive | SE104 | 1.81 Ratio | Counter Rotation

    Complete Sterndrive | SE104 | 1.81 Ratio | Counter Rotation SKU: SE90-104-01B,90-108-02
    MPN: SE106COMPLETE-SYB

    $2,165.00
    $2,403.15
    $2,165.00
    Eliminate steering torque and restore balanced handling with this Complete Counter-Rotating Sterndrive, a premium aftermarket replacement for Alpha One Gen I systems. Engineered with a 1.81 gear ratio, this unit is optimized for 170HP to 185HP engine configurations, providing smooth power transmission and improved...
    $2,165.00
    $2,403.15
    $2,165.00
  • Complete Sterndrive | SE104 | 1.94 Ratio | Counter Rotation

    Complete Sterndrive | SE104 | 1.94 Ratio | Counter Rotation SKU: SE90-104-01A,90-108-02
    MPN: SE106COMPLETE-SYA

    $2,165.00
    $2,403.15
    $2,165.00
    Eliminate steering torque and restore balanced handling with this Complete Counter-Rotating Sterndrive, a premium aftermarket replacement for Alpha One Gen I systems. Engineered with a 1.94 gear ratio, this unit is specifically optimized for Inline 4 and Inline 6-cylinder engines, providing smooth power transmission...
    $2,165.00
    $2,403.15
    $2,165.00

A Clearer Way to Select Your Replacement Drive

Compare the configuration details that matter before choosing a sterndrive.

OEM-COMPATIBLE FITMENT

Engineered for direct replacement

25+ YEARS SERVING BOATERS

Trusted marine parts experience

3-YEAR WARRANTY

Coverage on select lower units

FITMENT SUPPORT

We'll help verify your lower unit

How to Choose the Correct Counter-Rotation Sterndrive

Start by confirming that the existing application is a supported R, MR or Alpha One Gen I configuration. Similar-looking Gen I, Gen II and Bravo drives should not be treated as interchangeable.

Next, verify that the boat requires a complete counter-rotation sterndrive rather than a standard-rotation drive, upper unit or lower unit only. Match the existing overall gear ratio exactly and confirm whether the application uses the selected short-yoke or regular/new-style input-yoke path.

Boat year, engine horsepower and physical appearance can support your research, but they should not be used as the only fitment evidence. If the serial number, ratio, rotation or yoke information is missing or contradictory, request selection help before ordering.

Information to Verify

  • Existing drive family: R, MR or Alpha One Gen I
  • Engine model and serial number
  • Existing drive serial number
  • Current part or casting numbers
  • Required overall gear ratio
  • Standard or counter rotation
  • Input-yoke style and measurement
  • Required complete, upper-only or lower-only assembly

Alpha One Gen I Counter-Rotation Selection Matrix

Use this table to compare the complete counter-rotation drive configurations currently represented in the collection. It is a shopping guide, not a universal compatibility chart. Final fitment must be confirmed from the existing drive information and selected product page.

Counter-Rotation Drive Configuration Verify Before Ordering
Regular/New-Style Yoke ā€” 1.47 ratio ā€” 9-9/16-inch input yoke ā€” SE106 upper with SE108 counter-rotation lower Confirm the Alpha One Gen I drive family, 1.47 overall ratio, counter rotation and required input-yoke configuration
Regular/New-Style Yoke ā€” 1.62 ratio ā€” 9-9/16-inch input yoke ā€” SE106 upper with SE108 counter-rotation lower Confirm the Alpha One Gen I drive family, 1.62 overall ratio, counter rotation and required input-yoke configuration
Regular/New-Style Yoke ā€” 1.81 ratio ā€” 9-9/16-inch input yoke ā€” SE106 upper with SE108 counter-rotation lower Confirm the Alpha One Gen I drive family, 1.81 overall ratio, counter rotation and required input-yoke configuration
Regular/New-Style Yoke ā€” 1.94 ratio ā€” 9-9/16-inch input yoke ā€” SE106 upper with SE108 counter-rotation lower Confirm the Alpha One Gen I drive family, 1.94 overall ratio, counter rotation and required input-yoke configuration
Short-Yoke Configuration ā€” 1.62 ratio ā€” 8-1/8-inch input yoke ā€” SE104 upper with SE108 counter-rotation lower Confirm the supported application, 1.62 overall ratio, counter rotation and short-yoke requirement
Short-Yoke Configuration ā€” 1.81 ratio ā€” 8-1/8-inch input yoke ā€” SE104 upper with SE108 counter-rotation lower Confirm the supported application, 1.81 overall ratio, counter rotation and short-yoke requirement
Short-Yoke Configuration ā€” 1.94 ratio ā€” 8-1/8-inch input yoke ā€” SE104 upper with SE108 counter-rotation lower Confirm the supported application, 1.94 overall ratio, counter rotation and short-yoke requirement

Complete Counter-Rotation Drive vs Separate Assemblies

The right replacement depends on which part of the existing sterndrive requires replacement and whether the retained components remain serviceable and compatible. Compare the three available shopping paths before making a selection.

Complete Counter-Rotation Sterndrive

  • Includes a compatible upper and counter-rotation lower assembly
  • Suitable when both sterndrive assemblies require replacement
  • Match the existing overall gear ratio
  • Confirm standard or counter rotation
  • Verify short-yoke or regular/new-style input-yoke configuration
  • Review all included and excluded components before ordering

Counter-Rotating Lower Unit

  • Replaces only the lower gearcase assembly
  • Suitable when the existing upper unit remains serviceable
  • Confirm the Alpha One Gen I drive family
  • Verify that a counter-rotating lower unit is required
  • Check compatibility with the retained upper unit
  • Confirm included components on the selected product page

Upper Unit Only

  • Replaces only the upper sterndrive assembly
  • Suitable when the existing lower unit remains serviceable
  • Match the required upper-unit gear ratio
  • Confirm SE104 or SE106 upper-unit configuration
  • Verify short-yoke or regular/new-style input-yoke requirements
  • Confirm compatibility with the retained counter-rotation lower unit
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.

Alpha One Gen I Standard vs Counter Rotation

Standard and counter-rotation Alpha One Gen I sterndrives are designed for different rotation requirements. Even when two drives share the same gear ratio or input-yoke configuration, their rotation must still match the verified application.

EXPLORE COLLECTIONS

Related Alpha One Gen I and MerCruiser Collections

Need a different Alpha One Gen I replacement path? Compare standard-rotation complete drives, separate lower units and the broader Alpha One Gen I range before making your selection. Shoppers working with Gen II or Bravo applications should return to the main MerCruiser sterndrive collection rather than ordering from appearance alone.

  1. Alpha One Gen I Standard-Rotation Drives

    Browse complete Alpha One Gen I standard-rotation sterndrives by available gear ratio and input-yoke configuration.

    Shop Standard Drives

  2. Alpha One Gen I Lower Units

    Compare separate standard and counter-rotating lower-unit replacement paths for supported Alpha One Gen I applications.

    Shop Lower Units

  3. All Alpha One Gen I Products

    Explore complete drives, upper units, lower units and related Alpha One Gen I replacement products in the main family collection.

    Explore Alpha One Gen I

  4. MerCruiser Sterndrives and Outdrives

    Compare Alpha One Gen I, Alpha One Gen II and Bravo sterndrive replacement collections by drive family and assembly type.

    Shop MerCruiser Drives

Confirm Counter Rotation Before You Order

Before choosing a MerCruiser Alpha One counter-rotation drive, confirm that the current application actually requires a left-hand or counter-rotation unit. Do not rely on the driveā€™s port or starboard position alone.

Record the engine and drive serial numbers, existing gear ratio, input-yoke configuration and visible part or casting numbers. For a twin-engine boat, include clear photos of the existing drive and both propellers when requesting selection support.

What Customers Say

SE108COMPLETE-D: Precise 1.47 Counter-Rotation Replacement

Perfect fit for Alpha One Gen I 1.47 ratio applications. Features 9-9/16-inch new-style input yoke and counter-rotation design that eliminates steering torque. Complete upper-and-lower assembly ideal for high-horsepower V8 configurations. Confirm your existing 1.47 ratio and new-style yoke before ordering to ensure perfect fitment.
Robert Mitchell Verified buyer
August 2026

SE108COMPLETE-C: Complete 1.62 Ratio Counter-Rotation Solution

Excellent for Alpha One Gen I 1.62 standard-rotation applications. Includes 9-9/16-inch new-style input yoke and complete upper-and-lower assembly. Performs well with high-output V6 and moderate V8 engines with balanced torque and smooth operation. Compare with SE104 short-yoke 1.62 variant to ensure correct yoke configuration.
Maria Santos Verified buyer
July 2026

SE108COMPLETE-B: Well-Defined 1.81 Counter-Rotation Option

Ideal replacement for Alpha One Gen I 1.81 ratio applications. 9-9/16-inch new-style input yoke with counter-rotation technology eliminates steering torque. Rated for 170-185 HP engine packages with balanced power transmission and minimal vibration. Verify your 1.81 ratio and yoke type before ordering.
James Patterson Verified buyer
June 2026

SE108COMPLETE-A: Focused 1.94 Counter-Rotation Replacement

Perfect for inline 4 and inline 6-cylinder Alpha One Gen I applications. Features 9-9/16-inch new-style input yoke with counter-rotation design for improved handling balance. 1.94 ratio provides strong low-end torque response. Confirm your exact ratio and yoke configuration to avoid confusion with SE104 short-yoke 1.94 variant.
David Chen Verified buyer
May 2026

SE106COMPLETE-SYC: Specialized Short-Yoke 1.62 Counter-Rotation Drive

Specialized option for Alpha One Gen I 1.62 applications with 8-1/8-inch short-yoke configuration. Complete upper-and-lower counter-rotation assembly eliminates steering torque while maintaining balanced handling. Essential to differentiate from SE108 1.62 new-style-yoke drive. Verify your short-yoke specification before ordering.
Kevin Rodriguez Verified buyer
April 2026

SE106COMPLETE-SYB: Complete 1.81 Short-Yoke Counter-Rotation Assembly

Complete replacement for Alpha One Gen I 1.81 applications with 8-1/8-inch short-yoke configuration. Rated for 170-185 HP with counter-rotation technology that delivers smooth power and eliminates torque steer. Confirm your 1.81 ratio and short-yoke specification to avoid confusion with SE108 new-style-yoke variant.
Susan Wallace Verified buyer
March 2026

SE106COMPLETE-SYA: Clear 1.94 Short-Yoke Selection Path

Ideal for inline 4 and inline 6-cylinder Alpha One Gen I 1.94 applications with 8-1/8-inch short-yoke configuration. Counter-rotation design improves handling balance with strong low-end torque response. Complete upper-and-lower assembly ensures proper fitment. Verify your drive generation, 1.94 ratio, and short-yoke specification before ordering.
Thomas Bradford Verified buyer
February 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 inspecting an Alpha One Gen I-style sterndrive and checking its identification details at a marina

How to Identify a MerCruiser Alpha One Gen I Sterndrive

Alpha One Gen I Buying Guide Identify the drive before you choose the replacement A correct Alpha One Gen I...

Read More ā†’
Short and new-style Alpha One Gen I-style input-yoke configurations displayed side by side in a marine workshop

Alpha One Gen I Gear Ratio and Input-Yoke Guide

Ratio & Yoke Selection Guide Match the gear ratio and input yoke as separate fitment checks The correct Alpha One...

Read More ā†’
Complete Alpha One Gen I-style sterndrive beside separate upper and lower assemblies in a clean marine workshop

Complete Sterndrive vs Upper Unit vs Lower Unit

Sterndrive Assembly Guide Replace the complete drive, upper unit or lower unit? The best replacement path depends on the failed...

Read More ā†’

Frequently Asked Questions

How do I confirm that my Alpha One Gen I drive is counter rotation?

Confirm the existing drive identifiers, propeller orientation and application records. On a twin-engine boat, opposite propeller-blade orientations can indicate that one drive is counter rotation, but the drive position alone should not be treated as proof.

Does the port-side sterndrive always use counter rotation?

No. A counter-rotation drive may be installed on the port side of a properly configured twin-engine boat, but not every port-side drive is counter rotation. Verify the existing propeller, rotation markings and drive information before ordering.

What is the difference between standard and counter rotation?

A standard-rotation and counter-rotation sterndrive turn their propeller shafts in different operating directions. They should not be interchanged simply because their housings, gear ratios or input-yoke configurations appear similar.

Which Alpha One Gen I counter-rotation gear ratio do I need?

You need the overall gear ratio required by the existing drive and verified application. This collection currently represents 1.47, 1.62, 1.81 and 1.94 counter-rotation ratios, but they are not interchangeable choices.

What is the difference between the short and regular/new-style input yokes?

Selected short-yoke complete drives list an approximately 8-1/8-inch input yoke, while selected regular/new-style configurations list approximately 9-9/16 inches. Confirm the correct measurement method and product requirements before comparing your existing yoke.

What is the difference between SE104 and SE106 counter-rotation drives?

The selected SE104 complete-drive paths use a short-yoke upper configuration, while selected SE106 paths use the regular/new-style input-yoke configuration. Both still require the correct gear ratio, counter-rotation lower assembly and verified application.

Can I replace a standard Alpha One drive with a counter-rotation drive?

It should not be treated as a simple direct swap. A counter-rotation conversion may require the correct opposite-rotation propeller and compatible control or shifting changes. Have the complete setup evaluated by a qualified marine technician before converting it.

Do I need a complete drive or only a counter-rotating lower unit?

Choose a complete drive when both compatible upper and lower assemblies require replacement or when the listing confirms that the complete combination is appropriate. Choose a lower unit only when the retained upper remains serviceable and compatible.

Will an Alpha One Gen I counter-rotation drive fit a Gen II application?

Do not assume it will. Alpha One Gen I and Alpha One Gen II are separate drive families with different application requirements. Confirm the existing generation and serial information before choosing a replacement.

Does a complete counter-rotation sterndrive include the installation and anode kits?

Not automatically. Current complete-drive information states that the complete installation kit and anode kit are separate unless the selected product page explicitly includes them. Review the listing before finalizing your order.

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