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Thread: Harmonics ?

  1. #1

    Question Harmonics ?

    To the folks here that know something about this.

    I had a new 40hp fitted to my 4.2 tinnie. Upon testing there was a specific noise at about 8kph. Sounded very much like a dry bearing.

    It was worse when backing off the throttle.

    One dealer has told me it is Harmonics, being a vibration between motor and transom. I have added extra backing plates, with no difference.

    The motor has had its 20 hour service, yesterday and the noise is still there.

    My question is, has anyone here heard of this " harmonics " being an issue ?

    Oh, the dealers re-greased the thrust bearing and also replaced the thrust washer.

    Video here and turn up the volume to hear it.


    cheers

    Last edited by Lucky_Phill; 13-04-2021 at 07:58 AM.
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  2. #2

    Re: Harmonics ?

    Funny enough, my old Merc 2 stroke used to rattle/vibrate/buzz bad enough to make things rattle in the side pockets, but, only at low speed, when crabbing I have quite a distance at 4 knot speed limit, which is right at the vibration speed, so I had to speed (only a bit) or go idle slow, it was perfect above or below that certain RPM/speed, never heard of it on a 4 stroke though.

  3. #3
    Ausfish Silver Member
    Join Date
    May 2004
    Location
    cooloola cove

    Re: Harmonics ?

    while you at the speed where it at its worst get some one to move around to find the area where the noise come from. my ols stessel used to make a sound like that and it was at a frame near my feet.jammed a rag in there and it stopped,
    forgot about the rag one day and it started again,funny though when I changed the prop no more noise

  4. #4

    Re: Harmonics ?

    Is there a owners group on Facebook to ask other owners if they have had the issue too ?

    had to deal with harmonics in car race engines
    holden 6s valiant 6s all have points you couldnt hold revs at while racing or could snap cranks
    had some very high comp cortina motors and no harmonic balancer, use to rattle the shit out the gear stick at certain revs

  5. #5

    Re: Harmonics ?

    I've had the marine retailer out in the boat. We have pinpointed the noise to around the engine area.

    On that note, I might borrow a stethoscope and try to listen to find it.

    I was 99.9% certain it was within the motor somewhere, like the drive shaft.


    LP
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  6. #6

    Re: Harmonics ?

    Phill do you feel a noticeable vibration go through the tiller or the boat when it happens? Or is it just the noise? If the latter I would suggest its not a harmonics issue. Usually when you hit that point SteveJ was talking about you get a balance issue that will be a really noticeable vibration.
    Democracy: Simply a system that allows the 51% to steal from the other 49%.

  7. #7

    Re: Harmonics ?

    Hey Phill, had this happen recently on a quintrex. Sounded like it was coming from inside around tge floor near the engine. Sounded like a cracked weld. Ended up finding it was a little speed fitting thing on the transom. If you reached over the back and grabbed it the noise would stop. Might not be your issue but might not hurt to reach over and grab any transducers etc hanging off the back to rule it out

    Sent from my VOG-L09 using Tapatalk

  8. #8

    Re: Harmonics ?

    Quote Originally Posted by Lovey80 View Post
    Phill do you feel a noticeable vibration go through the tiller or the boat when it happens? Or is it just the noise? If the latter I would suggest its not a harmonics issue. Usually when you hit that point SteveJ was talking about you get a balance issue that will be a really noticeable vibration.

    No vibration through the tiller...


    cheers
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  9. #9

    Re: Harmonics ?

    Quote Originally Posted by wahoofishingcrew View Post
    Hey Phill, had this happen recently on a quintrex. Sounded like it was coming from inside around tge floor near the engine. Sounded like a cracked weld. Ended up finding it was a little speed fitting thing on the transom. If you reached over the back and grabbed it the noise would stop. Might not be your issue but might not hurt to reach over and grab any transducers etc hanging off the back to rule it out

    Sent from my VOG-L09 using Tapatalk
    I don't have a speed fitting.

    cheers
    Kingfisher Painting Solutions:- Domestic and Commercial.

    For further information, contact details, quotes or advice - Click Here





  10. #10

    Re: Harmonics ?

    I don't know if the smaller motors have them but I had to replace the cluster bearing on my 150hp, fortunately under warranty. Same thing, only came in at certain revs.

  11. #11

    Re: Harmonics ?

    There's an App for that Phil, see post #6.
    http://www.ausfish.com.au/vforum/sho...50#post1636550

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