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  1. #1

    Default NS3.5A vibration shaking the whole boat

    I have an old NS3.5A on an American 18' sailboat.
    It seems to have a lot of vibration that it didn't used
    to have. Shakes the bracket and the whole boat.
    Changing the throttle setting doesn't seem to help.

    Motor starts and runs well....plenty of horsepower.

    Could one of the magnets on the flywheel be shifted?
    Or, something else?

  2. #2
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    3,309

    Default Re: NS3.5A vibration shaking the whole boat

    If the flywheel magnet came loose, the motor would be severely off time, so that's doubtful, since it runs well. More likely the bracket tilt bolt and/or "distance piece" that separates the two halves of the transom bracket need to be snugged. I would put a piece of carpet, or better yet, rubber, between the boat bracket and the motor bracket. Also be sure that the boat bracket is snug.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  3. #3
    Join Date
    Aug 2017
    Location
    South Africa
    Posts
    175

    Default Re: NS3.5A vibration shaking the whole boat

    Is your prop still in good condition?

  4. #4

    Default Re: NS3.5A vibration shaking the whole boat

    I thought about that. There are no chunks taken out, or other damage to the propeller.
    Although, it is well worn. Also, the vibration does not seem to depend on the RPM of
    the engine. You would think that there would be a resonance point...but, no.

  5. #5

    Default Re: NS3.5A vibration shaking the whole boat

    I found that the swivel bracket "A" is quite loose on the stern bracket bolt
    as compared with another engine that has seen much less use.
    I rarely open the throttle more than one-third. I tried opening up
    more than two-thirds and it does smooth out. Time to replace
    some parts.....

  6. #6
    Join Date
    Aug 2017
    Location
    South Africa
    Posts
    175

    Default Re: NS3.5A vibration shaking the whole boat

    I was going to say to check the brackets next, Tohatsu unfortunately have very soft engine mounts and bracket bolts, this was the first thing we had to change out when I still raced Tohatsu .... Yamaha engine bolts are very strong, we raced those on the standerd ones ...

  7. #7
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    3,309

    Default Re: NS3.5A vibration shaking the whole boat

    Tighten the bolt that attaches the swivel bracket to the transom clamp brackets.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  8. #8

    Default Re: NS3.5A vibration shaking the whole boat

    Yup...I tightened the nut on the tilt bolt.
    Seems much better!

  9. #9

    Default Re: NS3.5A vibration shaking the whole boat

    The vibration and noise is bugging us, again.
    Is there any possibility the crankshaft bearings could be bad.
    Or, perhaps other bearings?

    How difficult is it to check this, and do a replacement if needed?
    I am mechanically inclined but might not have all the necessary tools.
    The bearings themselves look quite inexpensive.

  10. #10
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    3,309

    Default Re: NS3.5A vibration shaking the whole boat

    I highly doubt you have bad bearings. There are two ball bearings for the mains; if bad, odds are the seals would get damaged, and the motor might not start as a result. The rod is pressed as the crank is assembled, so if bad, you would need to replace the whole crankshaft. Seldom ever happens, unless someone forgot to add oil to the fuel. No, you probably just have something loose in the bracket assembly.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  11. #11

    Default Re: NS3.5A vibration shaking the whole boat

    Well, a similar engine (M3.5A) on another boat is running a lot smoother.
    I doubt the driveshaft or propeller shaft is bent....the shear pin would have snapped if we hit something.
    I really don't want to take it in for service as the cost will likely exceed the value of the engine.

    I noted that this motor has points. I believe the ignition is transistorized and the points wear very slowly.
    However, this motor has seen a LOT of use. The contact breaker is NLA. But, it looks like there is an adjustment.

    The only other thing is that the motor has been used in saltwater and never flushed (not so easy).
    I suppose the cooling passages may be plugged. Perhaps take the cylinder cap off and clean things out.

  12. #12
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    3,309

    Default Re: NS3.5A vibration shaking the whole boat

    What on Earth would that have to do with vibration? If your model is so old that it has points, forget servicing the ignition. Make sure all the bracket and swivel botls are snugged.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  13. #13

    Default Re: NS3.5A vibration shaking the whole boat

    Everything is tight.
    I tried swapping different engines amongst different sailboats with different brackets.
    All of the Tohatsu 3.5A engines on the boats with stainless sheet-metal brackets are prone to shake.
    Our Yamaha 2.5 HP engine does not shake on these brackets...it runs very smoothly.

    Seems that there needs to be some cross bracing or perhaps replacement of the
    sheet metal with some appropriate aluminum U-channel. I have fabricated a
    bracket with two pieces U-channel and a piece of wood in the past. Very solid!

  14. #14
    Join Date
    Jul 2019
    Location
    United States Destin
    Posts
    1

    Default Re: NS3.5A vibration shaking the whole boat

    It is necessary to check the brackets next to Tohatsu but unfortunately they can have very soft engine mounts but the bracket bolts were the first thing it 
we could replace! when I was still racing Tohatsu .... The bolts on the Yamaha engine are very strong

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