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Required for fitment review to confirm compatibility.
The OBR Mercury V8 counter-rotation lower unit is a remanufactured replacement gearcase for selected Mercury 250 HP and 300 HP V8 four-stroke applications requiring a 5.44-inch housing and 1.75:1 gear ratio. Counter-rotation versions are available with 25-inch XL or 30-inch XXL driveshaft lengths and black or silver finishes.
This page is limited to the four remanufactured ME-G8 counter-rotation configurations. Standard-rotation ME-G8 gearcases should be selected from the separate standard-rotation product page. Do not assume the engine’s position on a multi-engine boat confirms the required rotation; verify the current gearcase and propeller rotation directly.
Horsepower and model year alone cannot confirm fitment. Before ordering, match the complete Mercury engine serial number, engine family, original ratio, gearcase size, driveshaft length, rotation and selected SKU. The unit ships without gear lubricant and must be filled with the lubricant specified for the application before installation or operation.
Ideal Applications
Multi-Engine Offshore Configurations
Saltwater Fishing and Blue Water Cruising
Commercial Marine Duty
This ME-G8 counter-rotation series is offered for selected Mercury 250 HP and 300 HP V8 four-stroke outboards using a 5.44-inch gearcase and 1.75:1 ratio.
Available configurations are:
Provide the complete Mercury engine serial number before shipment. The selected configuration must also match the engine family, original gear ratio, housing size, driveshaft length, propeller-shaft specification and required rotation.
Compatibility with specific FourStroke, Verado, Pro XS, SeaPro or Mercury Racing model designations must not be assumed unless OBR confirms the engine serial number and application.
Before shipment, the selected SKU should be reviewed against the customer’s complete Mercury engine serial number, model designation, horsepower, model year, original gear ratio, gearcase size, driveshaft length, required rotation and finish. If any submitted detail conflicts with the selected configuration, the shipment should be paused and the customer contacted for clarification.
The carton, product label, shaft length, rotation and selected SKU should be inspected before release to the carrier. Do not state that the gearcase was bench-tested, pressure-tested or water-tested unless that process is documented for the individual unit.
OBR states that its gearcase assemblies ship without oil. Before installation or operation, fill the unit to the required level with the lubricant specified for the application and confirm proper shift adjustment. During break-in, avoid full-throttle starts, vary engine speed, do not exceed 75% throttle during the first five hours and avoid sustained full throttle during the following five hours.
On arrival, inspect the carton and gearcase before installation. Photograph punctures, crushing, water exposure or visible product damage, retain all packaging and contact Mariners Warehouse before installing or operating the unit.
| Specification | Mercury V8 Counter-Rotation Lower Unit | 250–300 HP |
|---|---|
| Manufacturer | OBR Parts & Marine |
| Product Family | ME-G8 Counter-Rotation Gearcase |
| Condition | Remanufactured |
| Compatible Engine Make | Mercury |
| Engine Architecture | Selected V8 Four-Stroke Applications |
| Horsepower | 250 HP and 300 HP |
| Application Window | Selected 2018–2026 applications; complete serial verification required |
| Rotation | Counter / Left-Hand Rotation |
| Gear Ratio | 1.75:1 |
| Gearcase | 5.44-inch Housing |
| Shaft Options | 25-inch XL and 30-inch XXL |
| Finish Options | Black and Silver |
| Counter-Rotation SKUs | ME-G8-24B-R, ME-G8-24S-R, ME-G8-25B-R and ME-G8-25S-R |
| Major Exclusions | Standard rotation, 20-inch counter rotation, 1.85:1 ratio and unverified Pro XS, TorqueMaster, SeaPro, Verado or Racing configurations |
Start with rotation, not horsepower. This page covers a remanufactured Mercury V8 counter-rotation lower unit for selected 250 HP and 300 HP four-stroke applications. A similar-looking standard-rotation gearcase is not interchangeable simply because the horsepower, color or housing appears the same.
Next, confirm the existing gearcase uses a 1.75:1 ratio and the larger 5.44-inch housing. Ratio changes can affect engine load and propeller speed even when a gearcase physically bolts to the midsection. The current counter-rotation ME-G8 options use either a 25-inch XL or 30-inch XXL driveshaft, so the existing shaft configuration must also be matched.
Finally, select the correct black or silver finish and verify the SKU against the complete Mercury engine serial number. Do not assume every FourStroke, Verado, Pro XS, SeaPro or Racing V8 uses the same gearcase. If any detail conflicts with the existing unit, pause the order and request a fitment review before installation.
Use CTRL + F or search below to find your engine model
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The product information made it easy to confirm the correct SE216 counter-rotation lower unit for the port side of my twin V8 300 HP setup. The left-hand rotation specs and serial number requirements were clearly explained. Verifying the exact configuration before ordering prevented any installation issues.
I appreciated that the counter-rotation lower unit options were clearly distinguished from the standard right-hand models. The fitment guidance for the 250 HP V8 4-stroke made selecting the SE216 replacement straightforward. Confirming your port engine's exact specs before checkout is essential.
The product page clearly detailed the heavy-duty housing and counter-rotation setup required for Mercury 250–300 HP V8 outboards. Identifying the correct shaft length for my port engine was simple with their fitment assistance. The packaging was incredibly secure for such a heavy item.
The most critical factor when replacing this unit was ensuring I ordered the left-hand counter-rotation model for my 300 HP V8. Comparing my engine model year and serial number against the site guide took all the guesswork out. Highly recommend using the fitment support.
The technical breakdown helped distinguish this SE216 counter-rotation gearcase from standard V8 units. The 250-300 HP compatibility details were accurate. I've had it in service for a while now, and verifying my engine serial number prior to shipping gave me full confidence in the purchase.
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