Whirring Sound in gear at idle

[davebuc]

Greetings,
I have a 2014 Nautique 200 Closed Bow
6.0 L engine
PCM 1.23:1 transmission
approx 1730 hours

I bought the boat (promo boat) from a Nautique dealer in December 2015 with 1370 hours.
Despite the hours, the boat seemed very well maintained mechanically and cosmetically.
The boat had a thorough service at that point (Dec 2015) including fuel filters, oil filter, new belts, plugs, plug wires and the transmission was serviced at that time.
I have done the winterizing (closed cooling system w/ heat exchanger) oil changes (including oil filters) since and annual maintenance (impeller, fuel filters, lube grease fittings).

Recently, I started hearing a quiet whirring sound from the back of the boat when the boat is in gear, at idle.
Does not happen in reverse. Reverse sounds the same as it always has.
The whirring sound goes away when the boat accelerates.
If you accelerate really slowly, the whirring switches for a split second to a higher pitched whirring and then goes away.
I have not sat in the back center of the boat to notice whether it is from the transmission, coupling, through hull drive shaft area, or strut.
Transmission fluid level is checked regularly and is good.

I am trying to understand if this is normal / not normal, what helpful next steps might be.
The dealer I purchased the boat from had a great service department, and is a couple thousand miles away.

Thank you for reading and pondering,
Dave

[bturner]

Always difficult (really near impossible) to determine if a sound is a problem without being able to hear it but based on your hours alone and assuming the fluid levels are up I would guess that you have a bearing starting to go. That the sound changes with the direction the prop is turning, it would lend itself to being an output shaft bearing as that is the one that would see a difference in load based on the rotation of the shaft. If you wanted to try and locate the area better you could use a stethoscope or a long screwdriver with the handle placed to your ear to prob different areas of the transmission to try and pinpoint the area the noise is coming from. My first place to prob would be the output shaft bearing location near the coupler.

Failing bearing noises typically start as a light whirling sound then transform into more of a grumbling noise and finally a squeal as the bearing rollers deteriorate or the bearing cages fall apart. The really good new for you is that you have a straight inboard. If its an output shaft bearing there's a good chance they could change it without even taking the engine/trans out of the boat.

[davebuc]

Update:
Yesterday, a mechanic friend I ski with spent some time investigating the noise with me. He used a mechanic's stethoscope. The noise was most prominent when he put the stethoscope's pick-up on the bottom of the hull behind the drive shaft packing area.

He put the pickup on different parts of the transmission and did NOT hear the noise. He also ruled out the engine compartment. Yesterday, the noise was not present in gear at idle. You had to give a little throttle in forward gear to hear the noise. (like around 750 rpm). The noise is still not present in reverse, even with a bit of throttle.

I see that there is a part called the strut bearing on nautiqueparts.
I don't know with what regularity they wear out or how difficult it is to replace if worn out.
https://www.nautiqueparts.com/produc...-for-1-shafts/

Thank you for reading,
Dave

[charlesml3]

Sure, could be the strut bearing. It takes a special tool to pull the old one out and put the new one it. It isn't all that bad though.

-Charles