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Thread: Boat vibration - not what you think it is

  1. #1

    Default Boat vibration - not what you think it is

    I took my boat (24-ft Bayliner, Mercruiser engine, Bravo 1 outdrive) to the mechanic a few days ago. Main reason was because I was starting to feel a vibration on the boat at idle, whether in gear or in neutral. I told them, as part of their checking into this problem, to remove the outdrive and check the ujoints and gimbal bearing. Something they would have probably done any way. Before they did that, they said they noticed a grinding (slight) sound that increased lots when the wheel was turned all the way or near all the way left and right. They found that the ujoints needed replacing and they did that. Said the gimbal bearing felt smooth and recommended not replacing it. Checked the alignment of the drive shaft and then put it back together and started it up. No change. Took the outdrive off again to re-check and also checked the gears which looked good. I asked if they checked the engine coupler and they said yes it looked fine. I asked if the bellows were dry and they said yes. They'd run out of ideas. I said to go ahead and replace the gimbal bearing just in case. Did that and still no change. Since they had no idea what to do to find the problem, I hauled the boat home. I put the muffs on the outdrive and started it up. Couldn't hear the grinding they were talking about, but the vibration was still there. At around 600-800 rpm the boat at times would even rock slowly on the trailer. This was in neutral. I looked where the outdrive drive shaft fits into the engine coupler while the engine was running. I could see the drive shaft, coupler, and flywheel all turning but seems like something didn't look right. Wasn't smooth, like something was not in line or maybe not balanced. Could be my imagination.

    I winterized the engine so now I've got to try over the winter to figure out what the problem could be. I really don't want to take it out next spring only to have something crater on me. The only thing out of the ordinary I'd done before the vibration started was that I launched the boat and after I'd warmed it up several minutes noticed that the outdrive was still in the trailer position. Never done that in 17 years. The intake was still in the water, so no overheating (had the impeller replaced by the mechanic just in case). Didn't hear any clanking or feel any vibration at the time. And didn't notice the boat vibrate until the following weekend. Would it have been possible to have bent the outdrive drive shaft when I'd run the engine with the outdrive all the way up in the trailer position? There are only so many moving parts that could be the problem I'd think. The two mechanics together have about 80 years experience, and I've always gotten excellent service there. Am open to any and all ideas.

  2. #2
    Supporting Member iofthetaiga's Avatar
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    Broken engine mount?
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  3. #3
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    did you try to run the engine without the drive connected? which mercrusier engine? oil pressure? aka a main failure? comp test? burnt valve at idle can be source. backed out flywheel bolts. dial indicator the crank run out. i would think shop dudes would have noticed a bent shaft when replacing the u joints.

  4. #4

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    The problem is the yoke spline shaft worn where the gimle rides on the shaft. Pull the drive and mic it. I'll try to remember to post what the OD of a new one is.

    I see this all the time after 600-1000 hours on my bravo drives. The wear is excellerated if the alignment is off and it's not really noticeable unless you measure or have a new one to compare it to. Takes only about an hour to swap and you can still keep the u-joint. Bring it by if it's something you don't want to tackle yourself. Replace the spline shaft and gimble and your vibrations will be gone.


    Hopefully this helps.
    Mel
    North River and Phantom Boat Dealer
    Mecury, FNM Diesel Engine, Hagglund sales and service
    Prop, Impeller & Alumimum boat repair, customization, & metal fabrication.
    Visit www.akfrontierfab.com

  5. #5

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    I'll check the engine mount tonight.

    I'll have to ask the mechanic if they ran the engine without the outdrive on it, plus the other possibilities.

    Mel - The outdrive has about 800 hours on it, so it falls within the range you provided. I'll ask the mechanic if he checked that wear point. He's out hunting for a few more days. Does your shop do outdrive work? If the mechanic didn't check for wear on the shaft and you guys do this kind of work I might see if I can bring it by. I've not taken the outdrive off before and would rather leave it to the professionals. Thanks.

  6. #6
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    i dont know a darn thing about the drive. engines are my thing, so disregard my thoughts.

  7. #7

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    Quote Originally Posted by skydiver View Post
    I'll check the engine mount tonight.

    I'll have to ask the mechanic if they ran the engine without the outdrive on it, plus the other possibilities.

    Mel - The outdrive has about 800 hours on it, so it falls within the range you provided. I'll ask the mechanic if he checked that wear point. He's out hunting for a few more days. Does your shop do outdrive work? If the mechanic didn't check for wear on the shaft and you guys do this kind of work I might see if I can bring it by. I've not taken the outdrive off before and would rather leave it to the professionals. Thanks.
    yes we do and can check and repair. I know I have Bravo X drive spline yokes in stock but may need to order your model unless they happen to be the same. X models have a larger u-joint OD so may not be the same. I'm 95% confident this is the problem especially if the unjoints have been replaced. Before you bring it in please call to verify if I have it in stock. I'll check tomorrow and if not I'll get one coming and once it's in we can schedule you in and have it done that day.

    Mel
    357-9323
    North River and Phantom Boat Dealer
    Mecury, FNM Diesel Engine, Hagglund sales and service
    Prop, Impeller & Alumimum boat repair, customization, & metal fabrication.
    Visit www.akfrontierfab.com

  8. #8

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    Mel - sent you a PM.

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