Mercruiser Alpha One SE104 Counter Rotation is the older model short yoke. You may use the chart to determine your gear ratio. You can select the gear ratio from the drop down on this page. We can supply 1.62, 1.81, & 1.94
1. Replaces most Mercruiser Sterndrives from 120-260 HP 1967-1990
2. Your Mercruiser Sterndrive must have trim and tilt to be able to use our replacement drive.
3. If your Mercruiser Sterndrive is between 1967-1969 you must verify that you have 13 splines on your upper driveshaft .
4. Ships in two boxes. Comes with 9-9/16 input yoke.
5. Does not include Complete Install Kit or Anode Kit. Please see related items below.
6. To determine if you have a counter rotation unit on your twin engine boat it is easiest to look at the props.
If the props are identical orientation, then they are both standards. If the prop blades are opposite, then the port should be a counter rotation
7. Please refer to the model chart below to find your proper Mercruiser Sterndrive Replacement.
These are typical applications, it is best to confirm your ratio by counting the teeth in the upper.
Although great care was taken in the creation of this guide, SEI cannot guarantee its accuracy.
Model Year Range Serial Range Notes
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.
SEI does not make this gear ratio. You could substitute a 1.47 ratio, but it would not be covered
under our 3 year warranty as it is over our 300 HP Limit