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Mercruiser Alpha One Replacement Upper Unit 1.81 w/ Short Yoke

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List Price: $1,169.99
Starting At: $974.99
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Sterndrive Engineering Mercruiser Alpha One Replacement Upper Unit 1.81 Ratio w/ Short Yoke

  • 1.81 ratio also replaces the 1.84 ratio
  • Comes with an [old style] 8-1/8" input yoke.
  • This drive is generally used on older inline 6 and 4 cylinder engines.
  • For Alpha One Gen I Sterndrives 1972-1990.
  • 3 Year Manufacturer's Warranty


  • Model: 470
    • Year Range: 1976-1982
    • Serial Range: 4208730-6225576
  • Model: 485
    • Year Range: 1980-1982
    • Serial Range: 4893835 and up

OE#: 5523A67

Item is subject to a 20% restocking fee (Boat Covers, Bimini Tops, Outdrives, Drop Ship Items and Special Order Parts)!

**Year, Serial Number, and Horsepower are required to order. Please contact us with this information after you place your order otherwise processing will be delayed.

How to Install Sterndrive Engineering Short Yoke

  • First, determine the length of your yoke. Newer styles are 9-9/16" and older styles are 8-1/8". Remove the clips that hold the u-joint together. You can use a screwdriver to push on it to make removing the slips easier. You may need to use the screwdriver on both sides.
  • After the clips are out, use a hammer to tap the u-joint in one direction until you can remove the cup on the opposite side. Use a suitable socket so you do not hit the yoke with the hammer. If the seal is stuck to the u-joint, use a small pick or screwdriver to remove it.
  • Using a socket of the appropriate size, pound the u-joint in the other direction. The purpose of the socket is so that you don't hit the u-joint post with a hammer. The socket should fit over the post and contact the body of the u-joint before the post.
  • With the yoke out of the way, you can start reassembly. Install both u-joint clips and the u-joint and check to make sure they rotate smoothly. If everything looks good, take them off. If you're experiencing rough rotation, your u-joint will most likely need to be replaced.
  • Install the yoke over the posts of the u-joint then insert both u-joint clips while centering the yoke.
  • Tap the u-joint together. You may be able to tap one side in all the way and put the clip in, or you may need to tap each side in a little bit at a time.
  • With both clips in, turn the yoke and see if it turns okay. If it is stiff, try hitting the opposite side.
  • You will need to grease the u-joints using a grease gun and grease that is approved for u-joints.

Sterndrive Engineering Model Chart

Refer to Sterndrive Engineering's model chart below to find your proper Mercruiser Sterndrive Replacement. These are typical applications; it is best to confirm your ratio by couting the teeth in the upper. Although great care was taken in the creation of this guide, its accuracy cannot be guaranteed.

 Model  Year Range  Serial Range  Notes (See Below)  Standard Rotation  Counter Rotation
 120,140  1967-1969  2062141-2791956  1,2,3,4,5,6  1.94  1.94 CR
 120,140  1970-1982  2791957-6225576  2,4,5,6  1.94  1.94 CR
 160  1967-1969  2065190-2763441  1,2,3,4,5,6  1.62  1.62 CR
 165  1970-1977  2763442 and up  2,4,5,6  1.62  1.62 CR
 225-S  1974  3856268-4200499  4,5,6  1.47  1.47 CR
 233  1975-1977  4200500  4,5,6  1.47  1.47 CR
 250  1977  4791300-4898729  4,5,6  1.47  1.47 CR
 260  1978-1982  4898730-6225576  4,5,6  1.47  1.47 CR
 470  1976-1982  4208730-6225576  2,4,5,6  1.81  1.81 CR
 485  1980-1982  4893835 and up  2,4,5,6  1.81  1.81 CR
 888  1971-1977  3106717 and up  4,5,6  1.47  1.47 CR
 898/228  1977-1982  4782330-622576  4,5,6  1.47  1.47 CR
 R/MR/Alpha One  1983-1990  6225577-OD469585  6,7    


    1. Unit has an 8 spline driveshaft on the lower unit. If your unit is original, you need to purchase a complete.
    2. Unit has a short yoke on the upper driveshaft. We refer to this as the “Old Style”
      • ***Applies to all inline 4 and inline six cylinder engines up until and including 1982***
    3. Unit must have trim and tilt for our Replacement to work. If it has two trim hoses going to each cylinder, it has trim and tilt.
    4. Unit has an eyelet on top cover. Replacement unit will not.
    5. Unit has a round cavitation plate on lower unit. Replacement unit will not.
    6. Unit may have an o-ring and/or a preload pin on lower unit driveshaft. The replacement will not.
    7. Gear Ratio must be confirmed. Chart below is typical applications, however there is no guarantee it is correct. To be safe it is best to remove the top cover and count the teeth on the upper gears.
 Engine Configuration  Horsepower  Gear Ratio  Tooth Count  Standard Rotation  Counter Rotation
 Inline 4 Cyl. 2.5L/3.0L  120,140  1.98/1.94  20/24  1.94  1.94 CR
 Inline 4 Cyl. 3.7L  170  1.84/1.81  17/19  1.81  1.81 CR
 Inline 6 Cyl.  160/165  1.65/1.62  24/24  1.62  1.62 CR
 V6 4.3L  185/190  1.84/1.81  17/19  1.81  1.81 CR
 V8 305 2 Barrel Carb.  200  1.65/1.62  24/24  1.62  1.62 CR
 V8 305/350  230/260  1.50/1.47  20/22  1.47  1.47 CR

pdficon.png Click Here to Download Short Yoke Installation Instructions

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