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Old 19-10-2016, 01:28   #1
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Vibrating shaft at slightly high revs.

I am attaching a clip which shows a disturbing vibrations at let's say when the engine is reving at or above lets say 2200 rpm.
I am looking for opinions on what might be causing this.
Keeping in mind that the shaft and bearings where replaced. Probably in a vain attempt to fix this.
Thanks.
I will post the video as soon as I figure out how.

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Old 19-10-2016, 05:09   #2
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Re: Vibrating shaft at slightly high revs.

First thing to do is check your propeller. Make sure it is clean, with no barnacles or growth. Also check for damage like dents, bends and chips from striking something or cavitation erosion.
This should always be your first step as its the easiest place to start (and probably the source of most peoples vibration issues).
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Old 19-10-2016, 06:31   #3
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Re: Vibrating shaft at slightly high revs.

Without the benefit of the video, and knowing if you're in gear and what exactly is vibrating, I'll throw these out there:

- Worn cutlass bearing (sounds like that was replaced?)
- Engine alignment
- Bent/damaged prop. If it's a Max prop, it might have been reassembled wrong, with one of the blades a degree mismatched
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Old 19-10-2016, 06:42   #4
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Re: Vibrating shaft at slightly high revs.

I am going through exactly the same thing, a harmonic resonance freq that suddenly makes the driveshaft whip like the washing machine does when it's out of balance.
I have

1. verified driveshaft straightness / run out
2 verified engine alignment
3. replaced cutlass bearing
4. replaced engine mounts
5 verified prop balance

My problem I believe is with driveshaft overhang, I have 2.5" sticking out and should ideally have no more than 1.5" or so. I have a 1.25" thick shaft.
I attached three shaft collar zincs to the driveshaft to the inside of the boat and removed the one outside and moved my resonance freq from 2200 to 2700, and in my mind validated that I simply have too much weight hanging off of a too long of unsupported shaft.

I am assuming your vibe like mine happens in gear when motoring forward and that it is a driveline vibration and not an engine vibration.
Lot of assuming.
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Old 19-10-2016, 08:30   #5
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Re: Vibrating shaft at slightly high revs.

Can you specify just how (method) you went about verifying your alignment, shaft, etc.?
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Old 19-10-2016, 09:27   #6
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Re: Vibrating shaft at slightly high revs.

Well I paid two years ago for the shaft to be removed and checked for straightness and the cutlass to be replaced and engine aligned.
Engine alignment is pretty straight forward your checking to ensure the coupling halfs touch each other perfectly is all.
But just put her in gear at idle and with one end supported push a pencil towards the turning shaft, if its not straight you will see a wobble, watch your hair loose clothing etc. of course. A dial indicator if your real anal is the way. Dial indicator, turn it by hand, motor off
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Old 19-10-2016, 09:58   #7
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Re: Vibrating shaft at slightly high revs.

My experience, most likely alignment. Insure shaft is centered before connecting, then check flange face alignment. It requires patience to repeatedly check, measure, then adjust the engine mounts; stay calm, do it right, be satisfied.
Let me know you need more help.
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Old 19-10-2016, 10:21   #8
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Re: Vibrating shaft at slightly high revs.

I don't see a clip. But some boats just have a vibration from the hull effecting the prop wash at certain rpms. Of course it could be many things.
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Old 19-10-2016, 11:37   #9
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Re: Vibrating shaft at slightly high revs.

Its funny! :banged:

I had a Pathfinder (VW) 50 in my boat for 29 years with a 1" prop shaft running different props without a problem. As soon as I repowered to a higher torque motor (Yanmar 3JH) I couldn't stop shaft vibration (whipping above 2200 rpm) no matter what was done, except in reverse, no problem. The boat was heavier though from major upgrades.
e.g. Alignment, balancing, soft coupler, new prop shaft, new prop, PSS to packing gland and even a Pythondrive installation. The final resolve was to up-size the shaft to the next size (1-1/8") which cured the problem.

The four main items that will affect vibration is the (1) coupler alignment, (2) cutlass bearing, (3) shaft and prop straightness and balance (4) motor mounting condition.

Check all these items. Going to a larger shaft is a total *refit/replacement from the back of the motor to the end of the prop.

*coupler, shaft, prop, stern tube, shaft seal/packing and strut/cutlass.
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Old 19-10-2016, 17:19   #10
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Re: Vibrating shaft at slightly high revs.

I had a vibration problem, rechecked all alignment tolerances, replace cutlass, still no good. Sent the prop out to be re-pitched, blades shortened slightly, re-balanced and polished, problem solved. My shaft is almost 7 feet long. the engine sits in the middle of the cabin.
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Old 19-10-2016, 22:35   #11
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Re: Vibrating shaft at slightly high revs.

https://youtu.be/fUkl3v5gD4k
I posted a short clip on YouTube. Hopefully this link will work.
Lokking at all the advice so far. And as i had this same problem before the work was done. I am leaning towards the prop being bent or similar.
Or the shaft is still missaligned.

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Old 19-10-2016, 23:09   #12
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Re: Vibrating shaft at slightly high revs.

I originally said that the wobble occurred at higher revs but i had a better look at it and its always wobbling at the stuffing box.
Summarizing.
The system has always wobbled ( not vibrated) at the stuffing box since I bought the boat.
1 year ago on advice from a shipwright, Surveyor. I replaced the cutlass bearing and rebuilt the skeg. New coupling and new shaft.
The problem is still there.
Its possible that before I purchased the boat that the prop hit something, sustained some damage thats not readily visible and bent the shaft in the process.
I think all things considered its either shaft alignment or the prop?


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Old 19-10-2016, 23:12   #13
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Re: Vibrating shaft at slightly high revs.

In the previous post it sounds like I did the work myself. Just to clarify. It was all professionally done as I don't have the expertise. But am learning fast.

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Old 20-10-2016, 03:27   #14
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Re: Vibrating shaft at slightly high revs.

Looking at that... it feels like the coupling to me.


Either the coupling faces are out of true or if you have a flexible coupling, it might have distorted and/or gone hard.
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Old 20-10-2016, 03:30   #15
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Re: Vibrating shaft at slightly high revs.

Quote:
Originally Posted by Hoohaa View Post
In the previous post it sounds like I did the work myself. Just to clarify. It was all professionally done as I don't have the expertise. But am learning fast.
With all deference to the many wonderful professionals on this forum, having the job done professionally, in my experience, is no guarantee it was done right.

That's the fastest thing I learned from having a few boat things done by "marine professionals".
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