Yamaha C60 knocking noise at higher revs

[dioggio]

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?

 

[dioggio]

Anybody?

 

[99yam40]

only thing I can think of is to bore scope stuck into the spark plug hole to inspect the top of pistons to see if those are hitting something that came loose, or carbon build up.
Might also check timing to see if it has moved too far advanced causing piston slap
I guess bad gas could also cause the fuel to burn too fast doing the same thing

 

[saltchuckmatt]

Anybody?

Did you run it without the cowl? Check to see if anything is hitting the flywheel. Otherwise I guess I would pull the gearcase and see if anything looks wrong with the pump or shift linkage. What does it do at WOT?

 

[racerone]

Compression test.-----Post your numbers.-----Check gear oil for metal bits.

 

[dioggio]

Thanks for the comments. will investigate your suggestions.

 

[saltchuckmatt]

Thanks for the comments. will investigate your suggestions.

Yes, and let us know if you resolve it.