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Volvo Penta AQ series Duo Prop gear ratio questions

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    Volvo Penta AQ series Duo Prop gear ratio questions

    Have an 82 Bayliner 2450 and swapped my 5.0 for a 5.7 efi vortec engine. I now want to swap my 270 outdrive for Volvo Penta AQ series Duo Prop 280 outdrive. There are some issues. (1) Gear Ratios. How do I identify the gear ratio of the duo prop? (2) What modifications are required. I understood that the transom might require some cutting for the 280 but not sure. If anyone has done this I would certainly appreciate the benefit of your experience.
    San Diego
    1982 Bayliner 2450
    GM 5.7 fuel injected Vortec Engine/Duo Prop
    1989 Wellcraft 170
    GM 181/Alpha Outdrive
    1986 Hunter H31 Sailboat
    Yanmar 20GM20
    1963 Wards Sea King 12'
    1963 Evinrude 5.5 hp

    #2
    ..................
    Originally posted by wufibugs View Post
    Have an 82 Bayliner 2450 and swapped my 5.0 for a 5.7 efi vortec engine.
    I now want to swap my 270 outdrive
    In 1982, you most likely have a 275 drive. Can you post a few photos of it?

    The 275 and later 280 transom shields are extremely similar.
    Both use the large shaft collar steering fork.
    Both will accept the AQ series 270, 280, 275, 285, SP suspension fork.


    for Volvo Penta AQ series Duo Prop 280 outdrive.
    By 1983, Volvo Penta had introduced the Duo Prop stern drive. Some called it a 280 Duo Prop.
    If you are buying an actual 280 DP, I would suggest pulling the prop shaft bearing carrier so that you can examine the insides!
    (there were some issues with the early DP that caused bearing adjustment shims to spin and cause damage)



    There are some issues. (1) Gear Ratios. How do I identify the gear ratio of the duo prop?
    Keep in mind that this is an "over-all" gear reduction, or a "final drive" reduction!
    In other words, it is a result of the reduction in both the transmission and the lower gear unit!

    Very simple. Remove the propellers, remove the ring anode, wire brush the AFT-most end of the bearing carrier housing, and expose the stamped-in numbers.
    You will want to see 1.95:1.

    NOTE: the 1.78:1 or 2.30:1 will not work with your engine!

    (2) What modifications are required. I understood that the transom might require some cutting for the 280 but not sure.
    Again, post a few photos of your stern drive and "transom shield".

    If you have the 275 transom shield, nothing will require modification.
    Plus, the 275 transmission can be used with the Duo Prop lower unit.... so you do not need to change transmission......... only the lower gear unit must be changed.


    If anyone has done this I would certainly appreciate the benefit of your experience.
    I have installed many Duo Prop drives over the years.


    NOTES:

    When removing the suspension fork hinge pins, use caution!
    These pins are soft, and can easily be expanded if driven on with a steel drift punch.
    Use heat to expand the aluminum bosses, and use a brass drift punch ONLY.


    if mixing/matching components, (such as installing a transmission onto a different Intermediate housing, or installed a lower gear unit onto a different Intermediate housing),
    you MUST go through the proper shimming procedure.

    Rick E. Gresham, Oregon
    2850 Bounty Sedan Flybridge model
    Twin 280 HP 5.7's w/ Closed Cooling
    Volvo Penta DuoProp Drives
    Kohler 4 CZ Gen Set

    Comment


      #3
      Rick, that was incredibly helpful and will do as you suggest. If the gear ratio is correct, will probably elect to install the entire unit. BTW, why will the other two ratio's you mention not work with the 5.7?
      San Diego
      1982 Bayliner 2450
      GM 5.7 fuel injected Vortec Engine/Duo Prop
      1989 Wellcraft 170
      GM 181/Alpha Outdrive
      1986 Hunter H31 Sailboat
      Yanmar 20GM20
      1963 Wards Sea King 12'
      1963 Evinrude 5.5 hp

      Comment


        #4
        ....................
        Originally posted by wufibugs View Post
        Rick, that was incredibly helpful and will do as you suggest.
        You are welcome!

        If the gear ratio is correct, will probably elect to install the entire unit.
        When we install a complete drive (i.e., the transmission, Intermediate housing and lower gear unit), we remove the transmission.
        We then hang the suspension fork (Intermediate housing and lower attached) and then install the transmission last!
        Trust me on this one..... it makes it so much easier!
        It will cost you two additional O-rings ONLY!



        BTW, why will the other two ratio's you mention not work with the 5.7?

        With the 2.30:1...
        It will be numerically too high..... and/or the reduction will be too low.
        The 2.30:1 "drive gear" (what some think is a pinion gear) will be smaller. Being smaller equals less gear tooth contact with the two "driven gears", of which makes this gear set not nearly as stout.
        Your 5.7L engine's torque will be too much for this gear set.
        The other issue would be propping it correctly!

        With the 1.78:1...
        It will be numerically too low..... and/or the reduction will not be enough for the 5.7L engine.
        The 1.78:1 "drive gear" will be larger of which is in our favor...... but the engine will not have the torque for the lessor reduction.
        The other issue would be propping it correctly!

        Rick E. Gresham, Oregon
        2850 Bounty Sedan Flybridge model
        Twin 280 HP 5.7's w/ Closed Cooling
        Volvo Penta DuoProp Drives
        Kohler 4 CZ Gen Set

        Comment


          #5
          One more suggestion....... make sure that you can remove both props (if the drive comes with props). If the B series props have not been removed, cleaned, greased and reinstalled routinely, they might be stuck!
          Stuck DPs can be a bitch to remove...... often requiring them to be cut off.


          .
          Rick E. Gresham, Oregon
          2850 Bounty Sedan Flybridge model
          Twin 280 HP 5.7's w/ Closed Cooling
          Volvo Penta DuoProp Drives
          Kohler 4 CZ Gen Set

          Comment


            #6
            Thanks, Rick. They were off when I got the drive. I will post pics of the current drive and get the ratio off the due prop. Been real rainy here in arid San Diego [something we're not used to] and I had the Bayliner battened down. Will undo the jumble of tarps when we get a break in the weather.
            San Diego
            1982 Bayliner 2450
            GM 5.7 fuel injected Vortec Engine/Duo Prop
            1989 Wellcraft 170
            GM 181/Alpha Outdrive
            1986 Hunter H31 Sailboat
            Yanmar 20GM20
            1963 Wards Sea King 12'
            1963 Evinrude 5.5 hp

            Comment

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