SE228 counter-rotation gearcase opposite-side profile
SE228 counter-rotation gearcase opposite-side profile

Mercury SE228 Outboard Lower Unit | Counter-Rotation V6 |SE90-228

$1,865.00
$2,051.00
$1,865.00
SKU: 90-228-A25
Product type: Lower Unit

Product Condition: New

Key Features :
  • Premium Marine Grade Cast Construction
  • Precision Machined Internal Gears
  • Counter Rotation Specialized Performance
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Subtotal: $1,865.00

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New SEI aftermarket counter-rotation gearcase
Seven verified engine, ratio and shaft configurations
15-spline propeller-shaft application
Three-year SEI fault-free limited warranty
Pre-shipment fitment review available
SE228 counter-rotation gearcase opposite-side profile

Mercury SE228 Outboard Lower Unit | Counter-Rotation V6 |SE90-228

$2,051.00 $1,865.00
SE228 counter-rotation gearcase opposite-side profile

Mercury SE228 Outboard Lower Unit | Counter-Rotation V6 |SE90-228

$2,051.00 $1,865.00
Engine Family, Gear Ratio and Driveshaft Length: 3.0L V6 2-Stroke | 1.75:1 C.R. | 25-inch XL | 90-228-A25

    The SEI SE228 counter-rotation lower unit is a new aftermarket replacement gearcase for selected Mercury 3.0L V6 two-stroke and legacy Mercury Verado applications using the 4.8-inch torpedo-style gearcase. Seven configurations are available across three engine families, so the correct unit must be selected using more than horsepower alone.

    Selected 3.0L V6 two-strokes use a 13-spline driveshaft, 15-spline propeller shaft and 1.75:1 gear ratio. Selected 2.6L inline-six Verado four-strokes use a 20-spline driveshaft and either a 1.75:1 or 1.85:1 ratio. The supported 1.7L inline-four application is a supercharged Verado using a 20-spline driveshaft and 2.08:1 ratio.

    Every SE228 variant on this page is counter rotation. Do not choose the unit solely by assuming a particular engine position always determines rotation. Confirm the existing gearcase and propulsion configuration before ordering.

    The SE228 does not replace a standard-rotation SE221, the larger 5.44-inch Verado gearcase, or Torque Master, Torque Master 2 and Sport Master applications using the 19-spline fat propeller shaft. Later V6 and V8 engines carrying the Verado name also use different gearcases.

    • Manufacturer: SEI Marine / Sterndrive Engineering
    • Product family: SE228
    • Condition: New aftermarket replacement
    • Rotation: Counter rotation
    • Gearcase family: 4.8-inch torpedo style
    • Individual SEI diameter specification: Approximately 4.88 inches
    • Propeller shaft: 15-spline
    • 3.0L V6 driveshaft: 13-spline
    • Verado driveshaft: 20-spline
    • Available ratios: 1.75:1, 1.85:1 and 2.08:1
    • Available driveshaft lengths: 25-inch XL and 30-inch XXL, depending on engine family
    • V6 application: Selected 3.0L V6 two-stroke, 200–300 HP
    • Inline-six applications: Selected 2.6L Verado four-stroke
    • Inline-four application: Selected 1.7L supercharged Verado four-stroke, 135–200 HP
    • Installation kit: Not included
    • Anode kit: Not included
    • Core return: No core requirement found; verify with operations
    • Warranty: SEI three-year fault-free limited warranty, subject to full terms

    Selected 3.0L V6 two-stroke applications

    • 200–300 HP
    • Counter rotation
    • 13-spline driveshaft
    • 15-spline propeller shaft
    • 1.75:1 gear ratio
    • 25- and 30-inch configurations
    • 4.8-inch/approximately 4.88-inch torpedo-style gearcase
    • SE218-to-SE228 transition occurs around serial number 1B504989
    • Exact serial-boundary treatment must be confirmed

    Selected 2.6L inline-six Verado applications

    • Four-stroke, supercharged inline-six architecture
    • Counter rotation
    • 20-spline driveshaft
    • 15-spline propeller shaft
    • 1.75:1 applications identified by SEI for 300 HP
    • 1.85:1 applications identified by SEI for 200–275 HP
    • 25- and 30-inch configurations
    • 4.8-inch/approximately 4.88-inch torpedo-style gearcase

    Selected 1.7L inline-four Verado applications

    • Four-stroke, supercharged inline-four architecture
    • Selected 135–200 HP applications
    • Counter rotation
    • 20-spline driveshaft
    • 15-spline propeller shaft
    • 2.08:1 gear ratio
    • 25-inch driveshaft only in the current SE228 family
    • Engine must be a supercharged Verado application
    • Counter rotation only: Every 90-228 variant on this page is counter rotation. Standard-rotation applications use a different product family.
    • Do not order by engine position alone: Confirm the required propeller rotation and existing gearcase configuration.
    • 4.8-inch torpedo family only: The SE228 does not replace the larger 5.44-inch Verado gearcase.
    • Check the propeller shaft: The SE228 uses a 15-spline propeller shaft. A 19-spline fat shaft indicates an excluded performance application.
    • Performance gearcases excluded: The SE228 does not replace Torque Master, Torque Master 2 or Sport Master gearcases.
    • Not every Verado fits: Later V6 and V8 Verado engines use different gearcases even when the exterior appears similar.
    • Inline-four limitation: The supported 1.7L inline-four must be a supercharged Verado. Similar non-supercharged inline-four engines are excluded.
    • Driveshaft splines differ: Supported 3.0L V6 applications use 13 splines; supported Verado applications use 20 splines.
    • Match the original ratio: Do not choose between 1.75:1, 1.85:1 and 2.08:1 using horsepower alone.
    • Serial number required: V6 applications near serial number 1B504989 require special verification.
    • Installation and anode kits are separate: These kits are not included with the SE228.

    Before shipment, the selected SE228 configuration is reviewed against the engine information provided with the order. Submit the complete engine serial number, model number, horsepower, engine architecture, existing gear ratio, driveshaft length and required rotation.

    The review should confirm:

    • 3.0L V6 two-stroke, 2.6L inline-six Verado or 1.7L inline-four supercharged Verado
    • Counter-rotation requirement
    • 13- or 20-spline driveshaft application
    • 15-spline propeller shaft
    • 4.8-inch torpedo-style gearcase
    • 25- or 30-inch driveshaft
    • Correct 1.75:1, 1.85:1 or 2.08:1 ratio
    • No 5.44-inch, Torque Master, Torque Master 2, Sport Master or later V6/V8 Verado conflict

    When the shipment arrives:

    • Inspect the carton for punctures, crushing, moisture or other damage.
    • Photograph visible packaging damage before opening the carton.
    • Retain the carton and internal packaging until the unit has been inspected.
    • Confirm the received SKU against the order.
    • Inspect the housing, skeg, driveshaft, propeller shaft and mounting surfaces.
    • Confirm the ratio, driveshaft length and rotation before installation.
    • Report visible transit damage before the unit is installed.
    • Do not install, fill, disassemble or operate a damaged or incorrect unit.
    • Have a qualified marine technician complete the final fitment and installation inspection.

    A pre-shipment review helps identify application conflicts but does not replace final verification by the installer.

    Quick Fitment Summary

    Specification Mercury SE228 Outboard Lower Unit | Counter-Rotation V6 |SE90-228
    Product New aftermarket counter-rotation replacement gearcase
    Manufacturer SEI Marine / Sterndrive Engineering
    Product family SE228
    Rotation Counter rotation
    Gearcase style 4.8-inch torpedo family; approximately 4.88 inches on individual SEI listings
    Propeller shaft 15-spline
    Engine family 1 Selected Mercury 3.0L V6 two-strokes with 13-spline driveshaft
    Engine family 2 Selected Mercury 2.6L inline-6 Verado four-strokes with 20-spline driveshaft
    Engine family 3 Selected Mercury 1.7L inline-4 supercharged Verado four-strokes with 20-spline driveshaft
    V6 serial transition SE218-to-SE228 transition occurs around serial 1B504989; verify exact boundary
    Gear ratios 1.75:1, 1.85:1 and 2.08:1 depending on engine family
    Driveshaft options 25-inch XL and 30-inch XXL; availability depends on engine family
    SEI SKUs 90-228-A25, 90-228-A30, 90-228-A25F, 90-228-A30F, 90-228-B25F, 90-228-B30F and 90-228-C25F
    Major exclusions Standard rotation, 5.44-inch torpedo, Torque Master, Torque Master 2, Sport Master and later V6/V8 Verado
    Not included Installation kit and anode kit

    How to Select the Correct SE228 Counter-Rotation Lower Unit

    Start by confirming that the existing application genuinely requires a counter-rotation lower unit. Counter rotation is common in multi-engine installations, but engine position alone should not be treated as final proof. Confirm the existing propeller and gearcase configuration.

    Next, identify the engine architecture. A selected Mercury 3.0L V6 two-stroke uses a 13-spline driveshaft and 1.75:1 ratio. The supported 2.6L inline-six Verado uses a 20-spline driveshaft and may require either 1.75:1 or 1.85:1. The supported 1.7L inline-four supercharged Verado uses a 20-spline driveshaft and 2.08:1 ratio.

    Confirm that the existing gearcase belongs to the 4.8-inch torpedo family and has a 15-spline propeller shaft. The SE228 does not replace a 5.44-inch Verado gearcase or a 19-spline Torque Master, Torque Master 2 or Sport Master unit.

    Finally, match the original driveshaft length. The SE228 family currently offers 25-inch and 30-inch configurations, but not every engine family receives both choices. Submit the complete serial number before ordering, particularly for 3.0L V6 engines near the SE218-to-SE228 transition.

    Application / Compatibility Guide

    Use CTRL + F or search below to find your engine model

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    What Customers Say

    Clear fitment process for Mercury V8 300 HP FourStroke

    The product details made it simple to confirm that the SEI SE228 lower unit was the correct replacement for my 2021 Mercury 300 HP V8. The 1.75:1 gear ratio, 20-inch shaft length, and serial-number verification steps were clearly outlined. Always verify your gear ratio before placing an order.
    Derek Sterling Verified buyer
    August 2024

    Helpful options for high-horsepower Verado setup

    I appreciated how clearly the SE228 lower unit options specified compatibility for late-model Mercury high-horsepower engines. The 25-inch XL shaft, 1.85:1 gear ratio, and serial-number guidance made the selection straightforward. Confirming your shaft rotation type in advance is a must.
    Trevor Callahan Verified buyer
    November 2023

    Useful information for late-model Mercury 250 HP V6

    The SEI Mercury SE228 page provided clear guidance on drive shaft lengths and mounting bolt alignment for my 2019 Mercury 250 HP. The 20-inch standard rotation unit was easy to identify, and the item arrived safely in heavy-duty foam packaging.
    Nathaniel Cross Verified buyer
    May 2022

    Easy to verify 1.75:1 ratio for offshore motor

    Matching the 1.75:1 gear ratio was the most critical step for this replacement lower unit. Mariners Warehouse made cross-referencing my engine year and horsepower very easy. I recommend double-checking your full serial number before buying.
    Julian Mercer Verified buyer
    September 2021

    Smooth packaging and performance for twin setup

    The SE228-specific documentation made it easy to choose the correct counter-rotation unit for my offshore boat. The shipment arrived without any damage. Installation was direct, and after completing the required 10-hour break-in period, performance has been rock solid.
    Gavin Rhodes Verified buyer
    April 2020

    Frequently Asked Questions

    What engines does the SEI SE228 lower unit fit?
    The SE228 fits selected counter-rotation Mercury 3.0L V6 two-strokes, selected 2.6L inline-6 Verado four-strokes and selected 1.7L inline-4 supercharged Verado four-strokes. Confirm the complete engine serial number, original ratio, driveshaft length, spline counts and torpedo diameter before ordering.
    Is every SE228 variant counter rotation?
    Yes. The 90-228 variants on this page are counter-rotation gearcases. A standard-rotation application requires a different product, such as the corresponding SE221 configuration when otherwise compatible.
    Does the engine position determine whether I need an SE228?
    No. Counter-rotation gearcases are commonly used in multi-engine installations, but engine position alone should not be treated as final proof. Confirm the existing propeller rotation and complete gearcase application before ordering.
    What is the difference between the SE221 and SE228?
    The SE221 covers supported standard-rotation applications, while the SE228 covers supported counter-rotation applications in the related 4.8-inch gearcase family. Engine architecture, ratio, shaft length and rotation must all match.
    What is the difference between the SE218 and SE228?
    The SE218 covers earlier selected Mercury 3.0L V6 counter-rotation applications, while the SE228 covers the later-style counter-rotation family and also includes selected legacy Verado applications. SEI identifies a transition around serial number 1B504989, but the exact boundary should be confirmed before ordering.
    Does the SE228 fit every Mercury Verado?
    No. The supported Verado applications are selected legacy 2.6L inline-6 and 1.7L inline-4 supercharged engines using the 4.8-inch torpedo family. Later V6 and V8 Verado engines use different gearcases.
    Does the SE228 replace a 5.44-inch Verado gearcase?
    No. The SE228 is intended for the 4.8-inch torpedo family, specified at approximately 4.88 inches on individual SEI listings. It does not replace the larger 5.44-inch gearcase.
    Does the SE228 replace Torque Master or Sport Master gearcases?
    No. The SE228 does not replace Torque Master, Torque Master 2 or Sport Master gearcases. These performance applications may use a 19-spline fat propeller shaft, while the SE228 uses a 15-spline propeller shaft.
    What gear ratios are available for the SE228?
    The SE228 family includes 1.75:1, 1.85:1 and 2.08:1 configurations. The correct ratio depends on the engine family and original application and should not be selected from horsepower alone.
    What driveshaft lengths are available for the SE228?
    The current SE228 family includes 25-inch and selected 30-inch configurations. The 1.7L inline-4 supercharged Verado configuration is currently represented only by a 25-inch option.
    How many splines does the SE228 use?
    Supported 3.0L V6 applications use a 13-spline driveshaft. Supported 2.6L inline-6 and 1.7L inline-4 Verado applications use a 20-spline driveshaft. SE228 applications use a 15-spline propeller shaft.
    Are the installation kit, anode kit and gear lubricant included?
    SEI confirms that the installation kit and anode kit are not included. Gear-lubricant inclusion must be confirmed by Mariners Warehouse before publishing a definitive answer.
    How do I verify my SE228 configuration before ordering?
    Provide the complete engine serial number, model number and horsepower, then confirm counter rotation, engine architecture, existing gear ratio, driveshaft length, driveshaft spline count, 15-spline propeller shaft and 4.8-inch torpedo-style housing.
    What warranty applies to the SE228?
    The assembled SE228 outboard lower unit carries SEI's three-year fault-free limited warranty, subject to the manufacturer's complete warranty terms, exclusions, documentation requirements and claim procedure.
    Can I return the SE228 after installation?
    No. Under the current Mariners Warehouse return policy, products that have been assembled, installed, used or rented are not eligible for a standard return. Inspect and confirm the unit before installation.

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