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  1. #1
    Join Date
    Jun 2002
    Location
    co.Wicklow, Ireland
    Posts
    506

    Default Can anyone diagnose this sound from alternator area / alternator belt ?

    Once or twice recently we've noticed an unusual high pitched sound for a short period after starting the engine. The other day, after starting the engine to get across a shipping lane, we noticed the same noise for a longer period (that's when this video was taken), shut the engine down and sailed back to port. On restarting the engine, same noise, but found it diminished at low revs (800-100 revs), so got back into harbour OK. I called the local mechanic who was on the marina to take a look, and about an hour or two later, he came over & I started it for him ... and no noise. He tightened the belt anyway (he said it was a bit loose - and it was a bit).

    The recent history is that the boat has had 800 mile delivery trip, and the belt was really, really loose when she arrived (with a lot of black dust in the area). I tightened it considerably after arrival, but it has obviously slackened a bit more.

    However, I'm not sure if this is the belt ?
    • I've never had a belt screeching before on car or boat, so I'm not really familiar with the noise , though a belt noise seems more like a squeal from what I can gather
    • Although I didn't find/show him the video until after tightening the belt, and was dubious about whether the sound would translate accurately on phone video , the mechanic didn't seem convinced that this was a belt noise.
    • The noise has been intermittent - sometimes after startup (diminishing after, or at low revs), and sometimes not - she ran for hours without a noise the other day back to our home port. Why would a belt noise be intermittent ?


    I've become aware that spraying water/wd40 on a noisy belt confirms a belt issue if the noise goes away when sprayed - will try that at next opportunity ?
    Another suggestion someone made locally was alternator bearings, does that sound a likely candidate ? Our summer cruise is only a number of weeks away, should I pick up a spare alternator as a precaution, or take it out for inspection at an auto shop or go ahead and replace it ? (£100-£120)

    Hopefully this video & sound will play.... many thanks for any input.

    https://photos.google.com/share/AF1Q...B1RVVVaXMtSS1n
    Last edited by aidancoughlan; 10-05-19 at 06:09.

  2. #2
    Join Date
    Aug 2016
    Location
    On a boat
    Posts
    407

    Default Re: Can anyone diagnose this sound from alternator area / alternator belt ?

    Alternator belt slipping a little under heavy load. Mine would do it occasionally when the batteries were down. Happen once on passage at night. I wasn't about to stop the engine at silly o'clock in the morning, so just gave it a little spray from time to time stop the squeak. Once at my destination I changed the belt, and all was right with the world.
    Last edited by Mikedefieslife; 10-05-19 at 06:28.

  3. #3
    Join Date
    Oct 2007
    Location
    Central Scotland
    Posts
    2,308

    Default Re: Can anyone diagnose this sound from alternator area / alternator belt ?

    The video is really short, doesn't make it easy, but this sounds to me more than a belt, perhaps a bearing in the alternator. Take the belt off and hand turn the alternator slowly to feel for roughness in the bearing. (not foolproof test, but if rough there's a problem). Try changing the belt if its been slipping and there's rubber off then its worn anyway, so a new one won't cost a lot. Tighten properly and run again to see.
    Geoff. C.: Galvanizer and anchor manufacturer.

  4. #4
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,181

    Default Re: Can anyone diagnose this sound from alternator area / alternator belt ?

    Quote Originally Posted by aidancoughlan View Post
    Once or twice recently we've noticed an unusual high pitched sound for a short period after starting the engine.
    Hopefully this video & sound will play.... many thanks for any input.
    The circumstances you describe suggest a slipping alternator belt but a cogged belt produces an unmistakable squeal ( like a piglet) if it slips. That is not what I hear in your video. You dont say if it is a cogged belt or not.

    If it keeps going slack after tightening beware........ It'll break soon!

    Take the belt off and spin the alternator by hand to feel and listen to the bearings.

    Its not driving the raw water pump so run the engine for a shot while with the belt off and listen , but watch the temperature.

    Run the engine and listen to various likely points like water pump and alternator bearings etc with a "listening stick" or an engineers stethoscope.

    Eventually replace the belt with a cogged one if its not already cogged. ( they last for ever and squeal like a piglet if they slip.)
    Last edited by VicS; 10-05-19 at 07:26.

  5. #5
    Join Date
    Nov 2009
    Location
    Home UK Midlands / Boat Croatia
    Posts
    18,621

    Default Re: Can anyone diagnose this sound from alternator area / alternator belt ?

    Quote Originally Posted by MM5AHO View Post
    The video is really short, doesn't make it easy, but this sounds to me more than a belt, perhaps a bearing in the alternator. Take the belt off and hand turn the alternator slowly to feel for roughness in the bearing. (not foolproof test, but if rough there's a problem). Try changing the belt if its been slipping and there's rubber off then its worn anyway, so a new one won't cost a lot. Tighten properly and run again to see.
    I agree with Geoff ... 110%.

    Richard

  6. #6
    Join Date
    Apr 2018
    Location
    Mooring, Faro
    Posts
    1,337

    Default Re: Can anyone diagnose this sound from alternator area / alternator belt ?

    That's not belt squeal, which usually only happens on acceleration or when heavy alternator loads come on. I would have the alternator checked by an auto electrical repairer, they can run them up to speed in test rig. If you want to rule out the alternator and check the engine water pump bearings, get an emergency fan belt and cut it to fit just from the crankshaft pulley to the water pump pulley.

  7. #7
    Join Date
    Apr 2005
    Location
    Shropshire
    Posts
    8,628

    Default Re: Can anyone diagnose this sound from alternator area / alternator belt ?

    Sounds like bearings to me but could be alternator or water pump. I it were the belt slipping, you'd see some black powder around probably.

  8. #8
    Join Date
    Jan 2015
    Location
    Live in Fareham Area, Boat in Gosport
    Posts
    859

    Default Re: Can anyone diagnose this sound from alternator area / alternator belt ?

    I have to agree it doesnt sound like belt slip, if it has been dusting then it would be worth gettting another belt anyway and changing it to see if it makes a difference, cogged are good as Vic has suggested. That is cheap and quick and will rule out the belt.

    It does however sound more like its a worn/dry bearing lets hope were wrong.

  9. #9
    Join Date
    Jun 2015
    Posts
    1,437

    Default Re: Can anyone diagnose this sound from alternator area / alternator belt ?

    Late to the party as usual, but I had an alternator sound exactly like that when a bearing failed. Cheap fix if you can find a convenient practitioner.

  10. #10
    Join Date
    Aug 2016
    Location
    On a boat
    Posts
    407

    Default Re: Can anyone diagnose this sound from alternator area / alternator belt ?

    If it's not belt sleep though, then why did it magically stop when the OP sprayed the belt?

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