G23 Transmission Noise Under Load (Normal or Not?)

[jpwhit]

The alignment isn't hard to check and there's no real risk in checking it yourself. You can't throw it off by unbolting the shaft coupler. No reason you can't unbolt it and check it on the lift. But while it's unbolted I would lower the lift and check it when the boat floating. It probably won't change unless your lift is putting a lot of unequal pressure on the hull. But having the alignment be correct when the boat is floating, is the condition that actually matters.

[jpwhit]

Also just occurred to me that any major attachments points to the drivetrain and hull not being properly torqued to could also contribute to this type of resonance vibration. And most of the examples I can think of with one exception are pretty easy to check.

Some examples
Engine mount to hull bolts
Engine mount to engine bolls
Engine mount adjustment points
Engine to vdrive bolts
Bolt that hold the flex plate to the flywheel (this one wouldn't be easy to check - requires removing v-drive)
Shaft Coupler Bolts
Shaft Coupler to shaft connection
V-drive flange bolt
Strut bolts to hull
Prop bolt

[bturner]

Agree with the above. I've done minor alignments on inboards and once on a vDrive. In theory, it's not hard to do and checking with the newer vDrives with the coupler out front should be fairly straight forward. My 95 Maristar's coupler was under the oil pan and a complete PITA. My 93 ProStar inboard with the engine cover off was a peach as was the 05 Response inboard we did. Take close pictures and watch the coupler closely as you unbolt the coupler, if you see it "spring" or move in any direction (this happened on the Response) as you unbolt it will indicate that the alignment is off without even using a feeler gauge. The 2 surfaces should basically mate without effort and very little clearance, I believe clearance is something like .003 max. There's a ton of YouTube videos on this and skidim.com had a series on this posted as well.

This should have been one of the checks at various hour inspections at the dealer but from what I've been told they don't actually get done a lot of times unless there's a noise or vibration complaint.

[Tom_H]

I would definitely check alignment. If you look underneath at the shaft in the through-hull, you can often get a general idea if it may be off. Engines can settle on the mounts over time, and can lead to the shaft being force low in the through hull, and resulting in some uneven load on the strut bearings (which may be the source of the sound at certain rpms).

[BasaltRMK]

All,

Thank so much for all the insightful input. I'll do some research on the potential alignment issues. Not anything I've ever delved into myself but I'll check some threads and videos. I agree that this should be something that the dealer checks during the various xx-hour services, but I'm not confident that that's happening.

But I still keep thinking - why is it reproducible every time I accelerate slowly, but never when I accelerate slowly? I realize that this puts different stresses on the various rotating parts, etc., but if it's an alignment issue...? Anyway, I'll dig in some more and talk to the dealer (as well as await their response on the video). Unfortunately, unless there's a major issue with the boat, they won't see it until fall, as I do all my own oil changes and similar regular maintenance. And they're a 12-hour RT away.

mpost - just to clarify: once i initially accelerate (slowly versus quickly), the resonance sound is either there or not there at all RPMs above plane speed. E.g., if I accelerate slowly, I get the sound and it keeps going wah-wah-wah at all RPMs, from plane speed to WOT. I can change RPM as much as I want, but the sound won't go away until I come off plane and basically get back down to idle. Same with if I accelerate quickly and don't get the sound - I can move around through any RPM above plane speed and the sound won't be present. Does that make sense (as I described it, not as to WTH is going on )?

Thanks again all,

- bob

[jpwhit]

BasaltRMK what you're describing is not uncommon with this type of resonance phenomenon. That's because once the resonance gets going it tends to keep going.

The most likely explanation for why it only gets going when you accelerate slowly is because when you accelerate quickly, the fast acceleration is putting a lot of forward force on the boat structure during the fast acceleration through the prop shaft. That pushing through the prop shaft during fast acceleration cause the natural frequency of the boat structure to change. Think of it as the prop shaft pushing really hard on the boat structure as tightening up everything that can wiggle.

Maybe an analogy will make a little more sense. Think of a guitar string. When you pluck the string, it vibrates at a certain frequency. If you tighten the string using the screws on the guitar, the tone gets higher. That guitar string is vibrating at its natural frequency. Your boat structure actually works the same way. Under fast acceleration the natural frequency gets higher just like it does for a guitar string getting tighter. In this case, the boat hull is getting tighter due to the higher pressure of the prop pushing on the structure of the boat.

To understand the whole picture, using the guitar string analogy, you may have to take my word for the next part because I doubt it's something you've observed. And I can't think of real world simple example. If you held some type of buzzer that vibrated right up against a guitar. And the frequency of the buzzer was pretty close to the natural frequency of one of the strings. The string would start vibrating at its natural frequency and you'd hear a similar "Wah Wah Wah" sound. The rate that the "Wah" repeats is called the beat frequency and is based on the difference in frequency between the two things that are vibrating.

If before you held the buzzer up to the guitar you tighten all the strings enough that none of their natural frequencies is near the frequency of the buzzer, none of the strings would start spontaneously vibrating and you wouldn't hear any "Wah Wah Wah" sound when you held the buzzer against the guitar. This is what I think's happening when you accelerate quickly. I

So for your case, the engine / v-drive is the buzzer, and your boat structure is the guitar string.

Up until your lasts post, I didn't understand that once your "Wah Wah Wah" sound started that it continued. That can happen with a resonance, but it's not the most common case. Often, you'd hear the "Wah Wah Wah" through a certain engine RPM range but it would stop at some higher RPM. That's what I thought was happening in your case.

Once the "Wah Wah Wah" sound is going, if you feel around and touch the safe things to touch around the engine, v-drive, and the boat structure around the engine, engine mounts, compartment dividers, etc, near the engine do you feel anything vibrating significantly or is vibrating with the same beat frequency as the "wah wah wah".

Given that once it starts the "Wah Wah Wah" continues I think this is something the Nautique dealer needs to help you figure out and get fixed. But given how far you are from them, I can certainly understand wanting to figure out out without such a long trip. I think when you interact with your dealer, it's pretty important for them to understand that once this vibration starts, it doesn't stop until you slow the boat way down. In my opinion that makes this a much more significant issue then if the sound was only transient through a certain RPM range during acceleration.

And it's certainly conceivable that something is wrong with the engine or v-drive that's generating an unusual vibration that's the catalyst for starting this resonance. But I think it's more likely that something is loose somewhere.

One more thing that could cause a vibration that could be the source of getting this all started. Does your prop and have any ding or other damage on it.

[BasaltRMK]

jpwhit - thanks so much for the long reply and helpful information. Sounds like you have a clear understanding of the issue. The guitar analogy makes perfect sense. When we're out tomorrow or this weekend we'll spend some time looking for loose bolts, fittings, etc. and feeling around for anything that might have any out-of-the-ordinary vibrations.

Regarding the prop - we've ruled that out: 1) The prop is in perfect condition, and; 2) we have the exact same issue with our second prop, which is also in perfect condition and happens to be a different pitch (our home lake is 8,000' elevation, we re-prop for Powell).

Thanks again!

- bob

[mpost]

All,


mpost - just to clarify: once i initially accelerate (slowly versus quickly), the resonance sound is either there or not there at all RPMs above plane speed. E.g., if I accelerate slowly, I get the sound and it keeps going wah-wah-wah at all RPMs, from plane speed to WOT. I can change RPM as much as I want, but the sound won't go away until I come off plane and basically get back down to idle. Same with if I accelerate quickly and don't get the sound - I can move around through any RPM above plane speed and the sound won't be present. Does that make sense (as I described it, not as to WTH is going on )?

Thanks again all,

- bob

Got it. As Jpwhit says that makes a difference in the understanding of the noise. Good luck in your investigation.

[Jbertram1245]

Hi all, thank you for all the advice and helpful insights. Over the weekend I have checked motor mounts, v drive support brackets, etc, to try and find anything that could be loose. Everything was tight. I did however notice that the shaft may be slightly out of alignment. Feeler gauge was tight between 10 o clock and 2 o clock if you envision the shaft coupling surface as a clock. On the lower portion 3 o clock - 9 o clock I was able to easily fit the feeler gauge inbetween the two surfaces. The strange thing is the gap only appeared after the boat was in the water. On the lift the feeler gauge was unable to fit between the surfaces anywhere. And as the manual states verify alignment in the water with full fluids and so I did.

Given this knowledge I know that the rear motor mounts would have to be lowered slightly to flush out the coupling surface. I’m still awaiting advice from the dealer before I start messing with anything. I have attached a video trying to replicate the video BasaltRMK took earlier in the week. As you can hear the noise is persistent whether I accelerate slow or I pin it. Over the past month this noise has become noticeably louder. After watching the video multiple times I’ve noticed the “wah wah wah” is considerably less noticeable at a gradual rpm to 25 mph. When I pin it, the noise is very pronounced. I’m questioning whether or not a very slight offset on the shaft coupling could cause something like this? It sounds as if something internal is off balance. Like Nautique Jeff originally stated.

Again, thank you for everyone’s helpful insights. I really appreciate everyone who has been helping to narrow down this issue!

-Jack

[BasaltRMK]

Jbertram1245 - well, if there was ever any question, 100% we’re dealing with the same exact sound. That new video really sealed it for me.

Interesting on the shaft coupling feeler gauge results. I didn’t get to work on mine, too many people on the boat Saturday and no boating Sunday. But will be getting out this week. Let’s keep the communication open and get this solved.

- bob

[BasaltRMK]

Hey Jbertram1245 - any progress on the issue, or input from your dealer? The noise was particularly loud today, so I spent a bunch of time on my belly checking connections, mounts, everything I could think of. Everything feels tight and looks good, and I’m hesitant to start messing with the mount adjustments. Any news on your side?

- bob

[Jbertram1245]

Hi BasaltRMK After the dealer reviewed the video they insisted that everything sounds normal. I adjusted the shaft alignment slightly and the noise has been reduced slightly. The noise is defiantly still there, which is still driving me crazy. Did you ever check the shaft alignment on your boat? Still stuck at a dead end as far as fixes.

[BasaltRMK]

Hey there Jbertram1245 - first off, sorry that it's taken me so long to reply. We've had a busy summer, family and friend visits, etc. Also, I'm embarrassed to admit - I don't own a feeler gauge. I know, the shame (especially since I wrench all the time on my sleds and dirt bikes). Anyway, I finally ordered one, will have it soon, and will check my alignment.

Disappointing about your dealer's response, the intermittent nature of it on my boat is clear evidence that it isn't normal functioning. Plus the fact that it appears to be a really rare issue.

Can you describe exactly what you did to adjust your shaft alignment? Adjusted the v-drive mounts per the manual? I get nervous about my warranty when it comes to motor and v-drive mounts...

Thanks,

- bob