85 hp intermittent noise at ± 2500 rpm.

[ocfcartucho]

I have a pair of 1998 yamaha 85 hp which after a while running one of them starts making a noise intermittently near 2500rpm. then to accelerate over the noise disappears 3000rpm. Any suggestions of what may be causing the noise is welcome.
thanks, ocf

[robert graham]

Can you describe the "noise"?....

[ocfcartucho]

85 hp intermittent noise at ± 2500 rpm.

Is like something loose.

[Twin 150's]

If the motors are conected by tie rod end(steering)check that they arn't all loose or worn as they do get a bit of vibration.

[ocfcartucho]

The tie rod was replaced by a new one, because it was a bit of wear. I perform this test today that was posted.

1.Remove all 3 spark plugs.
2.Rotate the flywheel by hand clockwise by hand while looking in the plug hole.
3.Rotate the engine untill the piston passes TDC and is on its way down the cylinder.
4.Insert a screwdriver into the plug hole so the tip just rests on the piston crown.
5. Give the scewdriver a sharp tap with the palm of your hand.
6. Look and listen for signs of excessive wrist pin play and a sharp matalic sound.

I found that the third cylinder of the right hand engine, has slight metallic sound. How can determine if is the connecting rod bearing or the small cylinder bearing?

[99yam40]

not sure what you are calling small cylinder bearing, but either wrist pin or the crankshaft/rod bearing inspection would need to split power head to inspect.

[robert graham]

I had an rattle which turned out to be one of those throttle/shifter black plastic sliding pieces on the starboard side of motor. It would just vibrate at certain RPM's....fixed it with a couple of tie-wraps and rubber bands. Hopefully yours is something simple like that.

[ocfcartucho]

I perform a compression test and the result was 90 psi in the three Cylinders, the specifications do in the service manual indicates 130 psi. How low can be compression acceptable, noise may come from a thick piston ring?

Thanks,ocf