Direct Replacement Mercruiser Sterndrives

SEI Aftermarket Sterndrives

SEI Marine Products manufactures direct replacement aftermarket Sterndrives for Mercruiser R, MR, Alpha One and Alpha Gen ll drives. All current SEI Replacement Drives come with a three-year, Fault-Free warranty even if the failure is due to lack of lubrication for engines not exceeding 300 hp.

*Note* your current Mercruiser Drive must have both trim and tilt to use a SEI replacement Drive Unit. If you are not sure about this look at one of the Hydraulic Cylinders on your drive. If the hydraulic cylinder has two trim hoses connected to it, you have trim and tilt. (Some early model Mercruisers only have one hose connected to the Hydraulic Cylinder and SEI Marine Products does not make a replacement Drive Unit for these applications.)

Early Mercruiser Sterndrives (pre 1983) with inline 4- & 6-cylinder engines require a shorter yoke size of 8-1/8” vs. the later style yoke measuring 9-9/16”. This is not a problem as SEI offers replacements for these models as well.

MerCruiser sterdrive yoke dimensions
Chart of MerCruiser sterdrive yoke dimensions

Do you need help Identifying your Drive Model?

The easiest way to determine your Drive Model is by the Drive Serial Number. However, that is not always an option.

The Mercruiser Pre Alpha, R, MR and Alpha one (with Trim and Tilt) were manufactured between 1975 -1990. The Alpha One Gen ll started production in 1991 to current date. If you are not sure because of modifications that may have been performed by a previous owner here are a couple ways to identify your drive:

  1. Gearcase shape:
    • On Pre Alpha and Alpha One Drives the top cap on the Gearcase is square in shape
    • On Gen ll the top cap is rectangular in shape
  2. Note the mounting location for the Hydraulic Trim/Tilt Cylinders
    • On the Mercruiser Alpha One & SE106 Drives they are located at the very Back of the gearcase
    • On the Mercruiser Gen ll & SE116 Drive Units the mounting location is approximately 6” from the end of upper gearcase

Twin Engine Applications for Mercruiser Alpha One / SE106 & Mercruiser Gen ll / SE116 Drive Units

If you have a twin-engine boat, there is a good chance the port drive is a counter (LH/left hand) rotation drive. SEI Marine Products makes counter rotation replacement lower units that can be ordered separately as well as completer counter rotation replacement Drives.

The best way to determine if you have a counter rotation drive is to compare the port side propeller to the starboard side propeller. Looking closely at the propellers you will notice the port propeller twist to the left and the starboard propeller twist to the right on counter rotating drives. If you do happen to have two propellers that twist to the right, you have two standard rotation drives. This is not uncommon on early twin engine applications.

Gear Ratios

Drive units come in different gear ratios to best match power output of your boat’s engine.

If you can’t read the gear ratio off the drive, there are a couple ways of determining the gear ratio. One way is by the engine model and hp. The other way is to remove the upper cap on the drive and count the teeth on the two gears. Below is a chart to help you find the gear ratio for your boat’s drive.

If you have any questions, call a specialist at Go2marine for assistance before ordering by engine or tooth count.

RatioDrive Gear TeethDriven Gear TeethOriginal Ratio Was
1.94 20 24 1.98
1.81 17 19 1.84
1.62 24 24 1.65
1.47 22 20 1.50

Accessories sold separately for installation:

Other Accessories:


Go2marine is ready to help you find the right replacement Sterndrive Unit for your boat along with the accessories to install it and keep it running for years.

For a limited time, we are offering Free Shipping to the contiguous (lower 48) states.

Call us today at (800) 998-9508 to get your boat outfitted with a new SEI Marine Products/Sterndrive Engineering aftermarket Drive

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