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3 Cylinder 4 Cylinder 1987 and up

Outboard Lower Unit - Mercury - 3 Cylinder 4 Cylinder 1987 and up

$USD 1,099.00

Replaces most Mercury Outboard lower unit 3&4 Cylinder 2-Stroke 1987 and newer 70-125 HP

Ratio/Type / Shaft

SKU: SEI-90-205 Category:

Product Description

Sterndrive Replacement, your marine products partner, holds Mercury Outboard 3 Cylinder, 4 Cylinder 1987 and up Lower Unit (Replaces most Mercury lower unit 3 Cylinder, 4 Cylinder 1987 and up 2-Stroke 1987 and newer 70-125 HP) from the aftermarket at a very reasonable price throughout the marine industry.
You can also obtain a warranty with your purchase, giving you access to 3 years of full coverage. All this, at your marine products Partner: Sterndrive Replacement.

  1. This unit will not replace a 3 jaw lower unit unless you also change the shift shaft in the midsection.Click Here for shaft installation instructions.
  2. Replaces most Mercury lower unit 3 Cylinder, 4 Cylinder 1987 and up 2-Stroke 1987 and newer 70-125 HP.
  3. Also replaces most Mercury lower unit 75-115 HP 4-Stroke below Serial #1B366822.
  4. This Replacement Mercury lower unit will only work if you have a 4-1/4 bullet diameter.
  5. This Replacement Mercury lower unit will not replace models with a plastic water pump housing.
  6. You must verify your lower unit Gear Ratio.
  7. 2.31 ratio is no longer available. 2.33 is the proper replacement.
  8. You must verify your Mercury engine type: Two Stroke Carb, DFI (Direct Fuel Injection), or 4-stroke.
  9. You must verify your shaft length.
  10. Your model # also indicates the shaft size. An L is a 20″ and an XL is a 25″. When in doubt, please verify.
  11. There is also an LL model which is a 22.5 Inch Shaft. We do not offer this shaft size.

2006 and up models may use a shif shaft system. The easiest way to identify it is by the amount of shift shaft sticking out from the shift bushing. If it measures 7/8 or 5-7/8, our unit will work. If the measurements are 3/4 inch long, our unit will not work. In the late 90’s, Mercury marine made a change to metric in line gear case.

The reverse gears and clutches were changed from 3 jaw to 6 jaw engagement. As a result, the distance between the forward and reverse gears increased. The existing shift linkage could not account for the increased clutch travel needed. The shift shaft and the linkage in the mid section were redesigned to compensate.

When replacing a 3 jaw gear case with a 6 jaw gear case, the shift shaft and linkage must be replaced. SEI parts number SEI-92-205-07K has a shift shaft and link as well as applicable bushing and nuts. Since the powerhead needs to be removed to replace the shift shaft in the mid section, our kit also includes a new powerhead base gasket. It is a universal kit that includes two powerhead gaskets, so use only the appropriate one for your motor.

This kit will work for 75 HP-125 HP. Tiller models do not require any modifications.

The OE case marking for 3- or 6-jaw units. You will notice on the 6 jaw units that there is a 45 degree machined line just foward of the trim tab bolt hole. A 3 jaw case will not have a 45 degree line. All SEI units are 6 jaw; however, they do not have a 45 degree machined line.

 Figure 1(Below):
Photo of 205 Measurements.


Gear ratio



Pinion tooth count



Fwd. and Rev. tooth count












2.31 (NLA Use 2.33)

















Additional information

Weight 55.0000 lbs