SEI Marine

Mercury 3 and 4 Cylinder Outboard Lowers

( 3 Reviews )

Mercury 3 Cylinder and 4 Cylinder Outboard Lower Units

  • Mercury 3 Cylinder and Mercury 4 Cylinder Outboard lower units replace most 3 & 4 Cylinder Mercury 2-Stroke 1987 and New 70-125 HP.
  • This unit will not replace a 3 jaw lower unit unless you also replace the shift shaft in the midsection.
  • This unit will only work if you have the 4 1/4 Bullet Diameter.
  • This unit will not replace units with a plastic water pump housing.
  • Brand new with a 3 year fault free warranty
    • You must verify your Gear Ratio. See Gear Ratio / Cross Reference
    • 2.31 ratio is no longer available. 2.33 is the proper replacement.
    • You must verify your engine type, Two Stroke Carb, DFI (Direct Fuel Injection), or 4-stroke.
    • You must verify your shaft length. See Shaft Measurement Example Below
    • Your model # can also tell you the shaft size. An L is a 20" and an XL is a 25". If in doubt, please verify.
    • There is also an LL model which is a 22.5 Inch Shaft. We do not offer this shaft size.
    • If you have any questions about your application, please call us at 423-213-4471

Gear Ratio / Cross Reference

Gear ratio

Pinion tooth count

Fwd. and Rev. tooth count




2.31 (NLA Use 2.33)







Shaft Measurement Example




INSTALL KIT IS AVAILABLE (New Nuts and Washers to Install the unit)

Anode Kit is Available - New Zinc Fin and Blocks that attach to the unit to prevent corrosion.

Current stock: 0

3 Year fault free warranty
Typically ships in 24 hours
$0.00 (Fixed Shipping Cost)

3 Reviews

12th Oct 2015

SEI lower unit good job

4 day shipping impressive, nice packaging no free t-shirt Only have 5 hours on it , but very quite and very smooth Cannot believe how smooth the shifting is. So far very happy.

19th Nov 2014

easy to install, smooth and quiet.

It was a snap to install. My mercury 2002 125hp runs quiet and smooth with better hole shots and smooth positive shifts. Just make sure everything is in neutral when installing, and line up shift linkage, and water pump. And then the best Part, it was cheaper than a rebuild.

Add a Review