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Yamaha C60 knocking noise at higher revs

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  • Yamaha C60 knocking noise at higher revs

    My C60 has developed a knocking noise at higher revs. It is unnoticable when running at low speeds or when not in gear.
    I did replace the water pump impellor last season. Afraid I can't remember whether that immediately preceded the appearance of the noise or not. I did not use the boat again after hearing the noise.

    Here is a video at around 3000 rpm
    and another at 1500rpm. Lower than that I can't hear it at all

    any ideas?

  • #2
    Is the propeller good and tight on the shaft?…..


    • #3
      only things I can think of is bad fuel causing detonation(fuel burning to soon before piston get to the top of cylinder), or piston hitting the head due to bad rod bearings or wrist pins


      • #4
        Thanks for the replies. I have had the prop off and I ran it without the prop and could not hear the noise, but the engine is very loud out of gear revving hard I could be missing it. I did retighten the prop hard. I have refilled the tank with fresh fuel. I need to get someone to drive it for me so I can determine if sound is coming from head or lower unit.


        • #5
          What year is the motor?… many hours of use so far(approximately)….. maybe just normal wear on motor….my 1999 C90 Yamaha has a lot of time on it and it rattles some like old 2 stroke motors will do. Maybe run the motor with the top cowling removed to try to identify the noise?


          • #6
            I think its a 96, I don't think it has been used for a lot of hours. I have tried with the cowling off. Noise no louder. I am waiting for a friend to come out on a test run with me so he can drive while I listen as it only happens when at higher revs in gear, I cant leave the helm.