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Required for fitment review to confirm compatibility.
The OBR Mercury V6/V8 counter-rotation lower unit family on this page covers selected Mercury-Mariner four-stroke applications that require a 1.85:1 gear ratio. The 4.8-inch configurations are cataloged for selected 175–300 HP V6/V8 applications with 25-inch or 30-inch shafts. The 5.44-inch configurations are cataloged for selected 175 HP, 200 HP and 225 HP V6 applications with 20-inch, 25-inch or 30-inch shafts.
Configuration must be selected by exact engine and gearcase information—not horsepower alone. Confirm the engine serial number, current gearcase or OEM number, counter rotation, 1.85:1 ratio, housing size, shaft length, finish and condition before ordering. The 4.8-inch counter-rotation options on this page are new and available in black or silver. The 5.44-inch counter-rotation options are available in black as new or remanufactured assemblies.
Ideal Applications
Multi-Engine Offshore Configurations
Saltwater Fishing and Blue Water Cruising
Commercial Marine Duty
This listing contains two different counter-rotation gearcase families:
Submit the complete engine serial number and current gearcase/OEM number for verification before shipment.
Confirm all of the following before ordering:
Do not select a lower unit solely from horsepower, model year or port/starboard engine position. Mercury model families can use different gearcases, ratios and configurations.
Before shipment, the selected OBR SKU should be reviewed against the submitted Mercury engine serial number, engine model, current gearcase or OEM number, horsepower, 1.85:1 ratio, counter-rotation requirement, housing size, shaft length, condition and finish. If the submitted information is incomplete or conflicts with the selected configuration, shipment should be paused and the customer contacted for clarification.
The package and selected-SKU label should be inspected before release to the carrier. Do not describe the unit as bench-tested or water-tested unless that test is documented for the individual assembly.
OBR states that its gearcase assemblies ship without oil. Before installation or operation, the gearcase must be filled to the required level with the lubricant specified for the application. Installation, shift adjustment and initial operation should follow the engine manufacturer’s requirements and OBR’s lower-unit break-in procedure.
When the shipment arrives, inspect the carton for punctures, crushing, water exposure or other visible damage. Photograph any damage, retain the carton and packaging, and contact Mariners Warehouse before installing or operating the unit.
| Specification | Mercury V6/V8 4-Stroke Lower Unit | 1.85:1 |
|---|---|
| Manufacturer / Brand | OBR |
| Compatible Engine Make | Mercury-Mariner |
| Product Family | Replacement outboard lower unit / gearcase |
| 4.8-Inch Applications | Selected 175–300 HP V6/V8 four-stroke applications |
| 5.44-Inch Applications | Selected 175, 200 and 225 HP V6 four-stroke applications |
| Rotation | Counter rotation (C/R) |
| Gear Ratio | 1.85:1 |
| 4.8-Inch Shaft Options | 25-inch XL and 30-inch XXL |
| 5.44-Inch Shaft Options | 20-inch L, 25-inch XL and 30-inch XXL |
| 4.8-Inch Finish Options | Black or silver |
| 5.44-Inch Finish | Black |
| Condition | 4.8-inch: new; 5.44-inch: new or remanufactured |
| Model Years | Confirm by engine serial number; the exact OBR SKU pages do not publish a universal year range |
| 4.8-Inch SKUs | ME-G6-73B-N, ME-G6-73S-N, ME-G6-74B-N, ME-G6-74S-N |
| 5.44-Inch SKUs | ME-G6-79B-N/R, ME-G6-80B-N/R, ME-G6-81B-N/R |
| Not Covered | Standard rotation, 1.75:1 ratio, TorqueMaster and other housing configurations |
Selecting a Mercury counter-rotation lower unit requires more than matching horsepower. First confirm that the existing application uses counter rotation and a 1.85:1 gear ratio. Next identify whether the engine requires the 4.8-inch or 5.44-inch gearcase family and match the driveshaft length.
The 4.8-inch OBR configurations on this page are listed for selected 175–300 HP Mercury V6/V8 four-stroke applications. They are offered as new counter-rotation lower units with 25-inch or 30-inch shafts in black or silver. The 5.44-inch configurations are listed for selected 175, 200 and 225 HP V6 four-stroke applications. These are available in 20-inch, 25-inch and 30-inch shaft lengths, with new and remanufactured black options.
Do not assume that two Mercury outboards with the same horsepower use the same replacement gearcase. Match the engine serial number, existing gearcase or OEM number, housing size, shaft length, rotation and ratio to the selected OBR SKU before checkout.
Use CTRL + F or search below to find your engine model
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The product information made it easy to select the correct 1.85:1 lower unit configuration for my V8 250 HP FourStroke outboard. The 20-inch shaft length, 5.44-inch gearcase torpedo specs, and serial number requirements were clearly explained. Verifying fitment details before ordering made the replacement seamless.
I appreciated that the V6 3.4L 4-stroke lower unit options were clearly differentiated from older two-stroke models. The 25-inch shaft, 1.85:1 gear ratio, and serial-number guidance ensured I received the exact fit for my 200 HP outboard. Confirming exact prop shaft and gearcase dimensions prior to checkout is key.
The page clearly detailed the 1.85:1 ratio and shaft specs needed for modern Mercury V8 four-stroke engines. Identifying the 20-inch shaft model was simple with the provided guidelines. Packaging was solid in a high-density shipping container, and mechanical fitment was exact.
The most critical factor when replacing this Mercury V6 four-stroke lower unit was matching the original 1.85:1 gear ratio and right-hand rotation prop shaft. Comparing my engine model year and shaft length specs against the site guide took all the guesswork out of the process.
The technical breakdown helped distinguish this 1.85:1 gearcase configuration from other ratios used across the V6 and V8 platforms. The 175–300 HP four-stroke compatibility details were accurate, and verifying my engine serial number with support before shipping gave me full confidence.
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