Spun hub or?????

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by SCORPIO, Aug 18, 2019.

  1. SCORPIO

    SCORPIO Well-Known Member SILVER Sponsor

    Apr 7, 2008
    Delaware
    1989 300 DA
    Twin 5.7 Merc Alpha I
    Last week took boat out for a run, first run in a few weeks. As I was bringing up the rpms to get on plane, at about 2000 rpm the port engine began to rev suddenly as if I shifted to neutral. I backed off to 1000 and all seemed normal and I repeated the process three more times, each time I got to 2000 or so the port revved with no noticeable increase in thrust. Boat is an 89 300 DA with twin 5.7s and Merc Alpha one gen one drives. Port drive is counter rotation. I removed prop when we got out of the inlet to our swimming spot. It has a rubber press in hub ( Rubex). It didn't look bad and I could not get it to slip with boat in gear and me pulling hard on a blade, but I'm not a 320 hp engine either. I smelled NO rubber odor while accelerating and the drive shaft seemed to be increasing in speed when engine free revved while trying to plane. Boat never heated. I'm hoping it's a spun hub and not the coupler
    BTW coupler is 4 yrs old and alignment in spring was perfect. I have not hit anything with either prop. Back in spring on initial launch, the shift cable which was new, was a bit out of adjustment and that drive didn't engage forward right away and revs built up and she slammed into gear hard. I adjusted cable at dock and been fine since. I'm wondering if that shock broke the hub free? Only thing I can think of unusual that happened. Aside from hub or coupler, what else should I check? I bought a new prop and a replacement hub and will try that next time I'm down.
     
    Last edited: Aug 18, 2019
  2. Lazy Daze

    Lazy Daze Well-Known Member TECHNICAL Contributor GOLD Sponsor

    Apr 21, 2009
    PA
    Various
    Various
    Hub or coupler are about the only two things that can cause that - other than internal gear damage. If you wrapped some weeds around the drive, though, that can cause ventilation.

    Any evidence of rubber dust/pieces in the bilge - by the coupler?

    Mark the rubber hub in relation to the center portion of the prop. See if the mark moves.
     
  3. SCORPIO

    SCORPIO Well-Known Member SILVER Sponsor

    Apr 7, 2008
    Delaware
    1989 300 DA
    Twin 5.7 Merc Alpha I
    Didn't notice any rubber dust in bilge, need to put an inspection camera in by coupler and look around. Prop did have s number of small barnacles on the blades even though its AF painted. It did sound like cavitation but other stbd prop has same growth and performed normally. Could growth on the bottom in front of drives produce any effect like this? It's hard to paint under trailer bunks and wondering if I have a bunch of fouling taking place? That didn't occur to me until now. I think I'll install new prop, check for coupler damage and try the boat and see what happens.
    Wouldn't damaged gears cause issues at all rpm ranges? Boat shifts fine, has normal operation in forward and reverse as long as you dont rev up above 2000.
     
  4. Lazy Daze

    Lazy Daze Well-Known Member TECHNICAL Contributor GOLD Sponsor

    Apr 21, 2009
    PA
    Various
    Various
    Most likely, yes. Once it's in gear, it's in gear. I was only mentioning that as a general statement.

    Yes, growth on the bottom of the hull or the prop could cause ventilation - cavitation is a different thing, centering around pressure.
     
    SCORPIO likes this.
  5. SCORPIO

    SCORPIO Well-Known Member SILVER Sponsor

    Apr 7, 2008
    Delaware
    1989 300 DA
    Twin 5.7 Merc Alpha I
    Yes ventilation.
     
  6. SCORPIO

    SCORPIO Well-Known Member SILVER Sponsor

    Apr 7, 2008
    Delaware
    1989 300 DA
    Twin 5.7 Merc Alpha I
    Finally got down to boat with good weather and installed new prop and hub, PROBLEM SOLVED! Boat ran great, got out of the hole and on plane just like its should. The old prop and hub look fine but obviously were slipping. I'll clean up the old prop, press out the old hub and install a new hub and carry as a spare.
     
    Little Ducky likes this.
  7. Lazy Daze

    Lazy Daze Well-Known Member TECHNICAL Contributor GOLD Sponsor

    Apr 21, 2009
    PA
    Various
    Various
    Good deal - easy fixes are nice. I would recommend having a prop shop do the rehab on your prop, though. They'll make sure it's balanced, too.
     
    SCORPIO likes this.

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