Mercruiser 3.0 unexplained rotational noise

[trooper1954]

Hi all,
Just put my boat in the water for the first time this season, and have noticed a rotational noise and slight vibration when in gear that increases with the rpm. This does not happen when out of gear. Can someone suggest where I start to diagnose what the issue might be?
Thanks

 

[Bondo]

Ayuh,..... The only thing that rotates in gear, but not in neutral is the prop shaft, so I guess the prop is a good place to look 1st,.....

 

[trooper1954]

Ayuh,..... The only thing that rotates in gear, but not in neutral is the prop shaft, so I guess the prop is a good place to look 1st,.....

Thx Bondo...the prop was replaced new last season and probably has 2-3 hours on it max. What should I be looking for with the prop shaft....do I need to pull the leg?
I was thinking maybe CV joint or. ...
Thx again

 

[Bondo]

Ayuh,..... Make sure the prop shaft is straight, 'n the prop ain't rubbin' on the lower unit,.....
As I said, Everything but the prop shaft turns in neutral, 'n you said the sound goes away in neutral,....

 

[trooper1954]

Thanks Bondo..... it's on the buoy at the moment so will check that later. I don't think there's anything rubbing on the lower unit but will check. If nothing's rubbing do I need to pull her out and take the leg off to see if the prop shaft is straight?

 

[Bondo]

Ayuh,..... If ya wanta get wet, do it in the water,....

With most boats, at full tilt, the prop is still underwater,....
No reason to pull the drive to check the prop,....

 

[ryan04]

I'd pull the the prop off completely (1 nut) and start it on the hose. Shift it into drive and see the vibration shows up at low RPM. Perhaps increase the RPM's a bit but not too much as back pressure is your friend. See if it shows up then. I'm no pro but that's where i'd start.

 

[Scott Danforth]

No need to pull lower, like bondo stated, only thing that does not turn in neutral is prop and prop shaft

Forgetting the thrust washer gor the prop will be a rubbing and grinding noise when in gear

 

[trooper1954]

Thanks guys for the advice...I'll take the prop off and run without to see what happens....altho I know when I replaced the prop last year I definately put the thrust washer back on...it ran without this noise/ vibration for 2/3 hours, and I have not touched the prop since.
Thanks

 

[nola mike]

Even though the prop is the only additional thing turning in gear, you aren't under load in neutral (and you said you were testing in the water and not on land). Certainly possible for u joints or gimbal bearing to only make noise when a load is applied. Does it vary with Drive position, steering angle?