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Diagnose Alpha 1 Problem

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  • Diagnose Alpha 1 Problem

    My friend's boat uses an alpha 1 outdrive, and there appears to be a serious problem---the motor runs fine but the prop doesn't turn. How can we diagnose what's broken?

  • #2
    There are several things that can go wrong between the engine and the propeller.
    1. Spun propeller hub. If you have an older style prop with the rubber hub it is a little harder to tell, but remove the prop and see if it looks okay. Newer style props have a plastic hub. Those are very easy to see if they are in good shape. Normally when a hub spins you are able to idle in gear with no problems, then when you accelerate you will notice the rpm's go up, but you will lose thrust.
    2. Engine coupler. The engine coupler is a splined aluminum tube surrounded by rubber. If the rubber has spun you might notice a burning rubber smell. You can also look inside the boat behind the engine and see if their are small pieces of burnt rubber by the input shaft. The splines could also strip out. The easiest way to know if that is the problem is to pull the drive and visually inspect the splines, both on the input shaft and on the coupler itself. With the drive removed you will be able to shine a flashlight in the gimble bearing area to see the slpines.
    3. Upper gearset. These will fail quickly if the drive runs low on gearlube. With the drive off, turn the input shaft clockwise (while standing in front of the drive). You should be able to feel if there are any problems. If it is locked up tight then you will need to separate the drive to isolate the problem. If it turns, look thru the exhaust passage at the verticle driveshaft and see if that is also turning. If it is not, then the upper gear set is bad, or the driveshaft broke right below the splines where it engages in the upper gearset.
    4. Lower gearset. With the drive separated, turn the verticle shaft clockwise (while looking down at it). It will be a little hard to turn if you still have the water pump on it. If it feels smooth then try to put it in gear. The shift shaft is in front of the verticle shaft. Turn it all the way clockwise for forward and all the way counterclockwise for reverse. If the prop shaft is turning smoothly while in gear, It should be fine. If it is not turning then you know you have a problem with the lower gearset, or the verticle driveshaft has broke above the pinion gear.

    Any further diagnostics will require special tools. If we can be of more help to you, please post or give us a call.
    Tech Support
    Brunswick Corporation is the original equipment manufacturer (OEM). Sterndrive Engineering, Inc. (or SEI) is not affiliated with the Brunswick Corporation and is not authorized to sell or service Brunswick products.