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Spun Prop Hub - Again-gctid390721

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    Spun Prop Hub - Again-gctid390721

    Last year about this same time, I spun a prop hub on my 1990 2556, 7.4L/B2.

    Did the same thing again this year.

    Something that the prop shop suggested I check is the proper amount of exhaust cooling water thru the center of the prop to cool the prop hub when under heavy load such as getting plane. Both times the hub spun was when getting on plane.

    Engine runs great and with normal water temp. Manifolds and risers don't seem to have excessive heat.

    I will be pulling the risers tonight and checking for restrictions, intact flappers etc.

    Other thought is the prop shop also said the Merc. props are famous for spun hubs.

    Any ideas?

    #2
    Sorry no help here but I do have a question. How do you know when you have spun a hub, what are the symptoms?

    Comment


      #3
      The symptoms are after throttling up say around 2000 rpm the boat seems to hit a wall and the rpm still advances.

      Doesn't the prop stay in the water i don't see spinning a prop can happen the way your so called mechanic describes it happening.

      The prop does not have any dings, scrapes. ?

      You hammering the throttle all the time ?
      Be good, be happy, for tomorrow is promised to no man !

      1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

      '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

      Manalapan N.J

      Comment


        #4
        I'm no expert, but wouldn't that also be when the prop is under the heaviest load?

        Was that a repaired or new prop? If repaired , maybe you need a new prop shop?

        Comment


          #5
          Sounds to me like your over torquing your prop hub. I would talk to some prop professionals before you go ripping your risers off. Tell them the brand and specs of the prop your presently spinning the hubs on. There are some different hub compositions and you may require one thats rated a little stronger for your hp.

          Comment


            #6
            Sounds like you might have too much prop for the load you are pushing. The prop shop should be able to help you best. It would help if you could tell them your RPM's at WOT and the approximate loaded weight of your boat. They should be able to tell you what you have there. Is it an OEM prop of something you or a prior owner put on there? Until you figure it out I would keep from WOT hole shots until you get those RPM WOT numbers and talk to the prop guys.

            Comment


              #7
              Buy a new prop and keep the re-hubbed one for a spare. Samething happened to me when I had my 3058 single engine boat. Spun the hub, prop shop re-hubbed it and it spun again on the first time out. I had them re-hub it, at the same time bought a new merc prop and just kept the re-hubbed one as a spare. I think once they go, the re-hubbed props are never as strong as the original.

              Comment


                #8
                driz wrote:
                Sounds like you might have too much prop for the load you are pushing. The prop shop should be able to help you best. It would help if you could tell them your RPM's at WOT and the approximate loaded weight of your boat. They should be able to tell you what you have there. Is it an OEM prop of something you or a prior owner put on there? Until you figure it out I would keep from WOT hole shots until you get those RPM WOT numbers and talk to the prop guys.
                I agree. I would also suggest you should use full tabs to help get her quickly out of the water which puts less strain on the prop. Actually the same strain but for half the time.

                I previously owned a 2855 with single 7.4 and Bravo 2 combo. Had everything including the kitchen sink in her and she was as butt heavy as they get. Never spun a prop in all the years I had here and actually never used tabs for hole shot either. Another possibility id the hub was defective from the get go.
                Cheers, Hans
                2007 Carver 41 CMY
                Twin Volvo D6-370
                Montreal, Canada
                Midnight Sun I Photos

                Comment


                  #9
                  Thanks for all the responses.

                  I've heard this from more then one source.

                  Theory on the exhaust heat is: The prop relies on the exhaust cooling water to keep the internal hub cool under heavy loads when the exhaust is hottest. The outside of the prop is in the seawater but the inside of a flow thru exhaust prop has the hot exhaust gas passing thru and not cold seawater.

                  This is a stock prop for this boat. 17.75 x 21P. Never had any issues with WOT, power, engine temps etc.

                  Yes, full tabs are used to get up on plane.

                  No, I'm not a full throttle Jockey. My engine is a 1990 raw water cooled and been in salt water all her life so I tend to baby her.

                  The intention is to purchase a new prop.

                  I'm leaning more towards the old prop not holding the hub. This is a very reliable prop shop doing the work and has stated these props are famous for spinning hubs due to high torque loads from heaver boats. They saw a lot of these when the Navy went to B2 drives on a lot of there boats.

                  I will continue to survey the risers. I pulled the stbd. side last night. Had a little blockage in the riser discharge tube at the boot. Nothing excessive. They were due for inspection anyway. I've been procrastinating on the inspection so this was a pressure point to get it done.

                  John

                  Comment


                    #10
                    Installed a new 17.75 x 21p Alum. prop. We'll see how she holds out. Engine was running a little on the rich side generating a little more heat but I wouldn't think enough to raise havoc with the bushing.

                    Ran great from the boat yard back to home port. Cruised about 25mph for about 40 minutes with no issues.

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