initial vibration of inboard prop when put in fwd or rev

Discussion in 'Inboards' started by Northeaster, Jun 23, 2017.

  1. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    Finished installing new Moeller 27 gallon tank and connecting lines as well as new Baldwin fuel water separator housing and filter (picked up at Parts for Trucks store for 1/10th of the price of a marine/ racor unit...)

    Started engine for 1st time since fall, and quickly tried engaging fwd and rev with new prop on - did not run for long and squirted some water on cutlass bearing just to give it a bit of lube before running.

    Took a quick video of prop going in fwd and rev - if you use settings to slow video down it looks like some vibration at prop - visible at prop nut, but seems to really smooth out once running and revved up a bit.
    Just wondering if it looks normal due to the whipping action of being engaged abruptly in gear and having shaft and prop go from idle to quickly doing 800+rpm at idle???? (its a 1:1 gear).

    If folks have a minute to watch the short video and give feedback, I would appreciate it!


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  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    It may just be that the engine shakes when you first put it in gear, and once it settles gets realigned.
     
  3. rxcomposite
    Joined: Jan 2005
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    Location: Philippines

    rxcomposite Senior Member

    My first thought is shaft misalignment but I think the water you squirted is not enough. It should be immersed in water for the bearing to "lubricate" or fill up all the clearance in the cutlass bearing. Try running with the prop fully immersed. Has it been in storage for long? The rubber bearing could have deformed.
     
  4. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    thanks for all input.
    It was only stored for about 8 months, and the bearing was new last year.
    Will run in water soon - yes, the prop stops abruptly when put back in neutral, so I think there is a fair amount of "grab" in the bearing without being fully immersed in water.

    Note - I think it ran quite smooth last year - you can see it running in other videos - and I have recently had the prop balanced, so I have no reason to believe it will not run fairly smooth.... I just noticed what looked like wobble at low speed in the video, and hence asked for opinions.
     
  5. rxcomposite
    Joined: Jan 2005
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    rxcomposite Senior Member

    It is not the grab on the rubber but the principle of the water "wrapping around the shaft" and being incompressible, provides the bearing surface. Might be a good precaution to check all the clearances around the bearing and shaft before you put in in the water. These rubber bearing do get oval after years of sitting in the dock with the shaft pressing down on the lower bearing surface.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    How long is the shaft, as it could simply be a little shaft whip at startup, as it initially picks up the mass of the prop. The above answers should be addressed, check alignment, balance, shaft trueness and bearings.
     

  7. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    shaft is 6 ft long, and is 1 1/4" diameter. I will see how it runs in the water in about a week. there is no play in the cutlass bearing - it is only 1 year old and has had perhaps 20 hours of use... I aligned the engine to a dummy shaft when I built the boat, welding up the strut and shaft tube to keep the shaft in alignment and build engine girders and mount supports. Then installed the real shaft, cutlass bearing and stuffing box and aligned the engine to the shaft using the mount adjustments.
    I have done this alignment process previously with my old sailboat. I will say though that I know the engine needs to be aligned to the shaft so that the coupler faces meet and mate well. But, unlike some shafts that have 2 fixed points (ie a cutlass bearings and perhaps an intermediate bearing or pillow block style bearing) which would prevent the shaft from having any play...- in a setup like mine, with the only bearings being a rubber cutlass bearing almost 6 ft away from the gear coupler - one is able to move the engine end of the shaft up and down and side to side a couple of inches likely , as the rubber bearing gives somewhat. So, I picked the spot in the middle of the shaft log and supported it there, while I then aligned the engine to it so that the coupler faces mounted squarely.
    As mentioned, it ran smooth last year - I juts noticed some whip or whatever in the video so I appreciate the feedback.
     
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