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Old 15-06-2016, 16:53   #16
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Re: Vibration troubleshooting help

What matters when you disconnect the coupling the flanges stay aligned. However some work involved in doing this... so you're going to pay for something I guess unless you start getting your hands dirty.
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Old 15-06-2016, 18:04   #17
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Re: Vibration troubleshooting help

I see two things. First thing is that the shaft should be centered in the bearing. From the photo it appears that the shaft is being pushed upward away from being centered. That might indicate the the forward end of the engine is lower than ideal or the the aft end of the engine is higher than ideal. Disconnecting the coupler and inspecting the alignment by measurement will tell the truth.
The other thing is that the vibration might or might not be related to alignment. You must find the actual frequency of the vibration in order to 'detective it' down to the truth. Vibration analyzers are expensive and complicated to operate. Except for the 'vibrating wire' tachometer, also called sirometer.



https://www.amazon.com/Briggs-Stratt...ords=sirometer

The base is held firmly to the engine while the vibration is at it's most evident. While holding the base turn the knob on top to extend the wire. As you extend the wire the painted end of the wire will vibrate and 'fan out' Adjust the knob in and out to get the widest 'fan'. Now pick up the sirometer and read the indicated number. This one shows both RPM and Hertz. Now, knowing the engine tachometer reading and comparing it to the sirometer reading will give you an idea how fast the vibration occurs compared to crankshaft speed. If the vibration occurs slower than the crankshaft then look at the transmission and drivetrain. If it occurs faster than the crankshaft speed look to the belt drives. If the vibration and the crankshaft speed are the same then you have a collapsed engine mount or some part of the boat is touching the engine, allowing a vibration path to the hull.

Short youtube video measuring lawn mower engine speed gives you and idea what the 'fan' looks like.



I've used the sirometer for measuring vibrations and speeds on projects ranging from model airplanes to dump trucks. Boats, too.
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Old 15-06-2016, 20:42   #18
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Re: Vibration troubleshooting help

^^I used a phone vibration frequency app in a similar way to a sirometer. Seemed to work ok, and narrowed the vibration down to shaft rotation frequency.

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Old 15-06-2016, 20:56   #19
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Re: Vibration troubleshooting help

if it were me, I would unbolt the shaft coupling, and then look to see if anything moves. if the shaft moves relative to the engine you have an alignment issue, if the shaft coupling stayed alligned wiht the transmission coupling, I would take a set of feeler gauges like I used to set the gap on spark plugs, and go around the coupling, that way I could see if the gap was the same all the way around.
What I would do is not necessarily what you should do.
good luck.
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Old 15-06-2016, 20:58   #20
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Re: Vibration troubleshooting help

So, the quick and cheap step to take is to disconnect the shaft (being sure that it cannot slide down the log and sink your boat!) and see whether the shaft is, at rest, in alignment with the engine. The photo appears to show a shaft out of alignment with the cutless bearing; if that is true then when released from the engine it is going to spring into alignment with the bearing (if it is not damaged) and out of alignment with the engine. The RPM issue is likely to be resonant frequencies in your hull.
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Old 16-06-2016, 03:30   #21
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Re: Vibration troubleshooting help

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Originally Posted by tkeithlu View Post
So, the quick and cheap step to take is to disconnect the shaft (being sure that it cannot slide down the log and sink your boat!) and see whether the shaft is, at rest, in alignment with the engine. The photo appears to show a shaft out of alignment with the cutless bearing; if that is true then when released from the engine it is going to spring into alignment with the bearing (if it is not damaged) and out of alignment with the engine. The RPM issue is likely to be resonant frequencies in your hull.
Hi, so what you suggest is pretty much the same feedback I have gotten this morning from speaking to various mechanic companies and the Beneteau dealer.

I appreciate your feedback and also the comments from the other members.

I will investigate how if it is within my comfort zone to detach the shaft.



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Old 16-06-2016, 03:41   #22
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Re: Vibration troubleshooting help

So to be clear, are we talking about undoing the bolts in the photo and seeing is the two flanges line up in there natural state?

A side question, how is the shaft attached to the flange with the bolts? Or will the shaft become loose when I unscrew the bolts?

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Old 16-06-2016, 03:44   #23
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Re: Vibration troubleshooting help

By the way I can spin the shaft by hand and it rotates perfectly smoothly. Would I feel a bad bearing if that was a problem?

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Old 16-06-2016, 05:35   #24
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Re: Vibration troubleshooting help

My bet is the prop. I had similar problems and had tje prop balanced and made true. Helped a great deal.

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Old 16-06-2016, 10:39   #25
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Re: Vibration troubleshooting help

Quote:
Originally Posted by AFKASAP View Post
So to be clear, are we talking about undoing the bolts in the photo and seeing is the two flanges line up in there natural state?

A side question, how is the shaft attached to the flange with the bolts? Or will the shaft become loose when I unscrew the bolts?

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The shaft will not become loose when you unbolt the coupling. It is very true that , although you may be out of alignment, it isn't necessarily the vibration problem. My 47 footer had a Nanni/Mercedes engine that at about 1500 rpm had a harsh vibration throughout the boat. It was not an alignment, bearing or motor mount problem. Nature of the beast I guess. I just avoided that rpm, but you have to pass through it going up and down.
Your problem sounds like a new one though, and hopefully it is that alignment.
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Old 16-06-2016, 11:09   #26
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Re: Vibration troubleshooting help

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Originally Posted by Cheechako View Post
The shaft will not become loose when you unbolt the coupling. It is very true that , although you may be out of alignment, it isn't necessarily the vibration problem. My 47 footer had a Nanni/Mercedes engine that at about 1500 rpm had a harsh vibration throughout the boat. It was not an alignment, bearing or motor mount problem. Nature of the beast I guess. I just avoided that rpm, but you have to pass through it going up and down.
Your problem sounds like a new one though, and hopefully it is that alignment.
Could be right. Even the Yanmar owners manual mentions some boats have a hull with a certain resonate frequency, and that engine rpm should be avoid for long periods.
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Old 16-06-2016, 11:11   #27
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Re: Vibration troubleshooting help

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Originally Posted by AFKASAP View Post
By the way I can spin the shaft by hand and it rotates perfectly smoothly. Would I feel a bad bearing if that was a problem?

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Probably not. Most bearing problems, unless the bearing is falling apart, will not indicate while turning the shaft slowly. If something is rubbing, you might hear or feel that while turning by hand.
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Old 16-06-2016, 11:14   #28
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Re: Vibration troubleshooting help

Quote:
Originally Posted by AFKASAP View Post
So to be clear, are we talking about undoing the bolts in the photo and seeing is the two flanges line up in there natural state?

A side question, how is the shaft attached to the flange with the bolts? Or will the shaft become loose when I unscrew the bolts?

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Suggest you also check the coupling. There should be a set screw to keep the prop shaft from sliding out of the coupling when going in reverse. My boat did not have this set screw for 10 years or more. Once when I was testing engine at dock in reverse, and ran it full throttle while tied up, the shaft slipped about 1/2 inch. I later drilled an indent into the shaft for a set screw (coupling already was drilled and tapped).
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Old 16-06-2016, 11:17   #29
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Re: Vibration troubleshooting help

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Originally Posted by AFKASAP View Post
Thanks. I replaced the cutlass and drip less shaft seal in October last year. There is very little play when I try to shake the prop.
I do not understand your last question about the shaft log.


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Last question I had is what is the picture actually showing? Is that the packing gland or a dripless gland? It almost looks like a cutlass bearing, but that should not be inside the boat hull.
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Old 16-06-2016, 11:24   #30
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Re: Vibration troubleshooting help

This basic boat maintenance 101. A simple engine/shaft alignment issue any boat mechanic should be able to do.
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