Mercury Lower Unit SE205 | 3 & 4 Cylinder Outboard Replacement (70–125HP)

If your Mercury outboard is losing performance or showing signs of wear, replacing the lower unit is the smartest move. The SE205 lower unit is engineered as a dependable aftermarket replacement for most Mercury 3 and 4 cylinder outboards, delivering smooth power transfer, improved durability, and long-lasting performance on the water.

Built for reliability, this unit supports multiple configurations including 2-stroke carb, DFI, and 4-stroke engines. Whether you're upgrading an older setup or replacing a worn-out lower unit, the SE205 ensures consistent performance across a wide range of applications.

Designed for marine enthusiasts who demand durability and precision, this lower unit is a trusted solution for restoring engine efficiency without the high cost of OEM replacements.

 Key Features

• Fits most Mercury 3 & 4 cylinder outboards (1987 & newer)

• Compatible with 70–125 HP engines

• Supports 2-stroke (Carb & DFI) and 4-stroke engines

• Available in multiple gear ratios (2.07:1, 2.33:1)

• Multiple shaft options: 20” and 25”

• Heavy-duty construction for long-lasting use

• Ideal aftermarket replacement for worn lower units

 Technical Specifications

Compatibility Notes

• Replaces most Mercury 3 & 4 Cylinder 2-Stroke engines (1987 & newer)

• Also compatible with 75–115 HP 4-Stroke engines (below Serial #0T801000)

• Will NOT replace 3-jaw lower units unless shift shaft is changed

• Not compatible with models using plastic water pump housing

• Requires correct gear ratio verification before purchase

 Application Guide (Important)

• 2.31 gear ratio is discontinued → use 2.33 as replacement

• Verify engine type: Carb, DFI (Direct Fuel Injection), or 4-stroke

• Shaft length:

  • L = 20"

  • XL = 25"

• Some models may have 22.5" shaft (not supported)

• Must have 4-1/4" bullet diameter

 Variants (Clear Explanation)

Each variant includes:
👉 Gear Ratio + Engine Type + Shaft Length

Example:

• 2.07 / 2-Stroke Carb / 20"

• 2.07 / 2-Stroke DFI / 25"

• 2.07 / 4-Stroke / 20"

• 2.33 / 2-Stroke Carb / 20"

• 2.33 / 2-Stroke DFI / 25"

• 2.33 / 4-Stroke / 25"

• 2.33 / Bigfoot 40–60HP / 20"

 Choose based on:

• Engine type

• Shaft length

• Required gear ratio

 What’s Included

• Complete Lower Unit Assembly

• Pre-installed internal components

• Ready-to-install design

 Important Notes

• Always verify engine serial number before ordering

• Professional installation recommended

• Contact support for fitment confirmation

• Incorrect selection may cause compatibility issues