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Required for fitment review to confirm compatibility.
The OBR Mercury V6/V8 4-stroke lower unit is a replacement gearcase cataloged for selected 175–300 HP applications requiring a 1.85:1 gear ratio, 4.8-inch gearcase and standard rotation. New and remanufactured options are available.
Buyers can select a 20-inch L, 25-inch XL or 30-inch XXL shaft configuration in black or silver. Each configuration uses a separate OBR SKU so the chosen condition, shaft length and finish can be matched to the order.
Horsepower and model year alone cannot confirm compatibility. Before ordering, verify the engine model and serial number, original gear ratio, gearcase size, shaft length and rotation. This product should not be selected for a counter-rotation, 5.44-inch, 1.75:1 or TorqueMaster application.
Ideal Applications
High-Horsepower Offshore Boating
Deep-V Hull Recreation
Commercial Marine Duty
Saltwater and Freshwater Navigation
This lower unit is cataloged for selected Mercury V6 and V8 FourStroke applications in the 175–300 HP range that originally use a 4.8-inch gearcase, 1.85:1 gear ratio and standard rotation.
Select the shaft length that matches the original configuration:
Black and silver are finish options and do not determine mechanical compatibility. Exact engine model suffixes and serial-number ranges are not currently documented on the public product page. Submit the complete Mercury engine model and serial number for verification before the order is released.
Do not order by horsepower alone.
Before shipment, the selected OBR SKU should be reviewed against the submitted Mercury engine model and serial number, original gear ratio, gearcase size, shaft length and rotation. If the submitted information is incomplete or conflicts with the selected configuration, the shipment should be paused and the customer contacted for clarification.
The shipping carton and SKU label should be inspected before release to the carrier. Do not state that the unit was bench-tested or water-tested unless the exact testing process is documented for that SKU.
OBR gearcase assemblies ship without gear oil. Before installation or operation, fill the unit with the lubricant specified for the exact Mercury application. Proper shift adjustment is required. Follow OBR’s lower-unit break-in procedure: avoid full-throttle starts, vary engine speed, remain below 75% throttle during the first five hours, and avoid extended full throttle during the following five hours. OBR break-in instructions
When the shipment arrives, inspect the carton for punctures, crushing, moisture exposure or other visible damage. Photograph any damage, retain all packaging and report the issue before installing or operating the unit.
| Specification | Mercury V6/V8 4-Stroke Lower Unit | 1.85:1 |
|---|---|
| Manufacturer | OBR Parts |
| Compatible Engine Make | Mercury |
| Product Type | Replacement outboard lower unit / gearcase |
| Condition Options | New or remanufactured |
| Cataloged Engine Range | Selected 175–300 HP V6 and V8 FourStroke applications |
| Application Years | Selected applications beginning in 2018; exact model and serial verification required |
| Gear Ratio | 1.85:1 |
| Gearcase Size | 4.8-inch |
| Rotation | Standard rotation; confirm with supplier before publishing |
| Shaft Options | 20-inch L, 25-inch XL and 30-inch XXL |
| Finish Options | Black or silver |
| OBR SKU Series | ME-G6-70, ME-G6-71 and ME-G6-72 |
| Major Exclusions | Counter rotation, 5.44-inch gearcases, 1.75:1 gearcases and TorqueMaster configurations |
| Required Fitment Information | Engine model, serial number, original ratio, shaft length and rotation |
Selecting a Mercury V6/V8 replacement lower unit requires more than matching the engine horsepower. First, confirm that the original gearcase uses a 1.85:1 gear ratio and the 4.8-inch housing. Mercury V6 and V8 engines may use other gearcase designs, ratios or performance configurations even when the horsepower and model year appear similar.
Next, match the original shaft length. The OBR ME-G6-70 series is cataloged for 20-inch L applications, the ME-G6-71 series for 25-inch XL applications and the ME-G6-72 series for 30-inch XXL applications. Black and silver are finish choices; they do not change mechanical compatibility.
This product is intended for the standard-rotation configuration. If the existing unit is counter rotating, uses a 5.44-inch housing, has a 1.75:1 ratio or is a TorqueMaster gearcase, select the corresponding alternative product instead. Submit the complete Mercury model and serial number so these details can be checked before shipment.
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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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