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The OBR Mercury L4 lower unit is a replacement gearcase for selected Mercury and U.S. Mariner four-cylinder two-stroke outboards. Separate configurations are available for 3-jaw applications from 1988–1997 and 6-jaw applications from 1998–2006, with 20-inch L and 25-inch XL shaft choices.
New and remanufactured versions are offered under the ME-G4-02, ME-G4-03, ME-G4-04, and ME-G4-05 SKU families. The correct unit depends on more than the horsepower shown on the engine cover. The complete engine serial number, model number, jaw style, shaft length, gear ratio, and rotation must be confirmed before purchase.
A 6-jaw gearcase may replace selected earlier 3-jaw applications only when the correct updated shift rod and conversion procedure are used. Do not assume the two jaw styles are directly interchangeable.
The gearcase ships without gear oil. It must be filled with the engine manufacturer’s specified marine gear lubricant and installed, adjusted, and broken in according to the applicable service information before operation.
Lower units are heavy, application-specific assemblies. Before shipment, the selected SKU and the customer’s engine information should be reviewed for consistency. Delivery estimates begin after order processing and do not include delays caused by incomplete fitment information, carrier disruptions, or address corrections.
| Specification | Mercury 110–125 HP L4 Lower Unit | 3-Jaw & 6-Jaw |
|---|---|
| Product | Replacement outboard lower-unit / gearcase assembly |
| Manufacturer / Brand | OBR Parts & Marine, Inc. / OBR |
| Compatible engine make | Selected Mercury and U.S. Mariner applications |
| Engine family | Four-cylinder inline (L4) two-stroke |
| Condition options | New or remanufactured |
| 3-jaw applications | 110, 115 and 125 HP applications listed for 1988–1997; verify the ME-G4-03 horsepower conflict before publishing |
| 6-jaw applications | 110, 115 and 125 HP applications listed for 1998–2006 |
| Shaft lengths | 20-inch L and 25-inch XL |
| 20-inch L 3-jaw SKUs | ME-G4-02-N (new) and ME-G4-02-R (remanufactured) |
| 25-inch XL 3-jaw SKUs | ME-G4-03-N (new) and ME-G4-03-R (remanufactured) |
| 20-inch L 6-jaw SKUs | ME-G4-04-N (new) and ME-G4-04-R (remanufactured) |
| 25-inch XL 6-jaw SKUs | ME-G4-05-N (new) and ME-G4-05-R (remanufactured) |
| Gear ratio | VERIFY BEFORE PUBLISHING — confirm from the complete engine serial number and selected OBR SKU |
| Rotation | VERIFY BEFORE PUBLISHING — confirm from the engine serial number and existing gearcase |
| 3-to-6-jaw conversion | A 6-jaw replacement may be used on selected earlier 3-jaw applications only with the correct updated shift rod and written fitment confirmation |
| Gear oil | Ships without oil; fill with the manufacturer-required marine gear lubricant before operation |
| Warranty | OBR two-year limited gearcase warranty; terms and exclusions apply |
| Required fitment data | Complete engine serial number, model number, horsepower, year, jaw style, shaft length, existing gear ratio and rotation |
| Core charge | VERIFY BEFORE PUBLISHING — confirm the charge, refund amount, deadline and return freight for each SKU |
| Major exclusions | Do not use for three-cylinder, V6, Optimax/DFI, four-stroke, BigFoot, Command Thrust or high-performance gearcase families without written fitment confirmation |
Choosing a Mercury L4 lower unit requires matching the complete gearcase configuration, not simply selecting 110, 115 or 125 HP. Start with the engine serial number and model number, then identify the clutch style and shaft length already used on the engine.
The earlier 1988–1997 application group generally uses a 3-jaw gearcase. The later 1998–2006 group uses the 6-jaw configuration. Twenty-inch L applications use the ME-G4-02 or ME-G4-04 SKU families, while 25-inch XL applications use ME-G4-03 or ME-G4-05. Each family is available in new and remanufactured condition.
A 6-jaw unit may be used on selected earlier applications only when the correct updated shift rod and an approved conversion procedure are used. It should not be treated as an automatic bolt-on replacement.
Before ordering, confirm the serial number, model, year, horsepower, jaw style, shaft length, gear ratio and rotation. The replacement gearcase also ships without gear oil, so the required marine lubricant and installation supplies should be prepared before the unit is operated.
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The product information made it easy to determine the correct clutch jaw configuration for my 1996 Mercury 115 HP L4 inline-4 outboard. The 2.07:1 ratio, 20-inch shaft length, and serial number checks were clearly detailed. Verifying the clutch jaw count before ordering is crucial.
I appreciated that the product page explained the differences between the 3-jaw and 6-jaw lower unit designs for 110-125 HP L4 engines. Mariners Warehouse fitment assistance confirmed my engine year and serial range prior to purchase, saving me time.
The unit arrived securely boxed with heavy-duty foam protection. The drive shaft splines and 20-inch shaft lined up perfectly on my L4 engine. Shifts cleanly and runs quiet after following the gear lube fill and break-in guidelines.
Matching the gear ratio and checking the jaw type was straightforward for my 120 HP outboard. The gearcase functions smooth on the water, though unbolting the shipping bracket and lining up the shift shaft took a little extra patience during installation.
Replaced the worn gearcase on my 1994 Mercury 115 HP L4. The product listing clearly detailed fitment warnings and shaft length parameters. After filling with high-performance gear lube and following break-in hours, it has performed flawlessly.
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