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Old 06-28-2017, 11:55 AM   #1
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Slow motion video of my engine and shaft vibration

Hi everyone, this came up in my survey when I bought the boat but there is a slight vibration on the starboard engine. It doesn't happen in neutral, only in gear, and its significance changes based on rpm. We don't feel any vibrations in the boat except for in certain sea states such as a decent following sea. Maybe the props are loaded a different way when they are pushing water backwards and a following sea applies pressure forward. Not sure if this is normal behavior or if it is related to what you see in this video and just magnified.

In any case, since the engine is smooth as silk in neutral I assume this is either a shaft or prop issue.

If you don't mind taking a look at the video and letting me know what you think, that would be great. In the video you can see the engine shake a little bit, and you can see an oscillating movement at the shaft seal.

https://www.icloud.com/sharedalbum/#B0g5VaUrzM1kTu

Thanks,
Mike
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Old 06-28-2017, 12:02 PM   #2
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It does appear you have a bent shaft.
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Old 06-28-2017, 12:06 PM   #3
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I agree, bent shaft.
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Old 06-28-2017, 12:13 PM   #4
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I can't see what others obviously see on my iPhone. Now I am curious!
What are you seeing that makes it appear a bent shaft?
I am not disagreeing, just trying to file away info for future use...
Bruce
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Old 06-28-2017, 12:39 PM   #5
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Beware of internet guesses.....

Vibration could be prop damage, growth on a prop, cutless bearing issues, misalignment, transmission issues, etc....

Guessing from a short video without tons of other info is only a wild guess.
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Old 06-28-2017, 12:54 PM   #6
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I'm noticing the entire rear of engine move about as much as shaft moves at drip-less stuffing box.

Makes me wonder about the cutlass bearing at strut by propeller. And/or the strut itself for alignment as well as regarding its tightness to boat bottom.

Seems to me that if the prop was even a little out of balance if the strut was loose or cutlass bearing had problems the same wobble could become an issue that alters its intensity at different rpm. Wonder if the cutlass bearing has disappeared?
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Old 06-28-2017, 01:18 PM   #7
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Quote:
Originally Posted by Bruce B View Post
I can't see what others obviously see on my iPhone. Now I am curious!
What are you seeing that makes it appear a bent shaft?
I am not disagreeing, just trying to file away info for future use...
Bruce
I can see a wobble in the shaft as it is rotating. Looking at the aluminum stanchion, you can see the transmission moving and also looking at the packing gland you can see it wobble.
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Old 06-28-2017, 01:22 PM   #8
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Now it is possible that the problem lies with the engine mounts being loose and engine torque transferring to the transmission to wobble and making it appear the shaft is bent. But one thing for certain, that shaft is not running true through the bulkhead gland.
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Old 06-28-2017, 03:18 PM   #9
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My wild internet guess would be that the engine is not aligned and/or engine mounts are loose or damaged.

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Old 06-28-2017, 03:27 PM   #10
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To me, the wobble is so slow I would suspect a bent prop blade, fouled prop, worn cutless or bent shaft long before an engine issue. I stink at video guessing but it seems to wobble at a some fraction of the shaft revolution.
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Old 06-28-2017, 03:39 PM   #11
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Quote:
Originally Posted by psneeld View Post
To me, the wobble is so slow I would suspect a bent prop blade, fouled prop, worn cutless or bent shaft long before an engine issue. I stink at video guessing but it seems to wobble at a some fraction of the shaft revolution.
Well, keep in mind that the video was taken at 240 frames per second. The wobble you are seeing wouldn't be visible to the naked eye.

I am actually having the engines serviced Friday. I will have him take a look and check engine alignment and see what else he might be able to diagnose.

Mike
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Old 06-28-2017, 04:23 PM   #12
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I agree that it could be may different things causing the wobble. A bent shaft can pretty easily be determined by measuring the runout on the shaft. Put a dial gauge on the shaft, and slowly rotate the shaft by hand through a full revolution, while watched the dial gauge. Allowable runout varies with shaft diameter as I recall, so some research will be required to sort out what's allowable for your shaft. If the runout is good, then any wobble is dynamically induced, not the result of a bent shaft
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Old 06-28-2017, 04:36 PM   #13
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It looks like a bent shaft but could it also be a seriously out of balanced prop? I would see about maybe getting a diver to pull the prop and see if the problem goes way. If not, then it would be the shaft.
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Old 06-28-2017, 05:28 PM   #14
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It does appear you have a bent shaft.
yep!
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Old 06-28-2017, 05:31 PM   #15
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Wow...I guess I will post all my equipment failures on you tube so a 10 second video is 100 percent capable of diagnosis.
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Old 06-28-2017, 05:36 PM   #16
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Originally Posted by MichaelB1969 View Post
Well, keep in mind that the video was taken at 240 frames per second. The wobble you are seeing wouldn't be visible to the naked eye.

I am actually having the engines serviced Friday. I will have him take a look and check engine alignment and see what else he might be able to diagnose.

Mike

Not sure what you are inferring?

That a video of a guy walking with a limp wouldn't be noticeble?
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Old 06-28-2017, 05:48 PM   #17
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Either the stern bearing is worn or the alignment. Slack your coupling bolts so there is minimum space and use a feeler gauge and check the gap. Rotate 90 and check again. It should be within .002". By moving front or rear of engine/trans, up, down, right or left, alignment is adjusted. This is the old way, but has worked for me for 50 years.
My alignment is so close, I have to leave my engines in gear when docked or anchored in a current. Otherwise the shafts endlessly turn.
The average owner usually does a better alignment than the average mechanic/boat yard.
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Old 06-28-2017, 06:20 PM   #18
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Wow...I guess I will post all my equipment failures on you tube so a 10 second video is 100 percent capable of diagnosis.
By the way, I do realize that it is tough to internet video diagnose problems that could have a variety of causes. However, I am a novice, so at this point any sort of helpful guidance is appreciated. In fact, the feedback has already been helpful in that I've learned that the problem could be something other than a bent prop or shaft. The fact that it could be a bearing, or engine alignment are things I didn't know before posting. So in that sense I find the feedback beneficial even if it doesn't tell me that my specific issue is X or Y.
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Old 06-28-2017, 06:27 PM   #19
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By the way, I do realize that it is tough to internet video diagnose problems that could have a variety of causes. However, I am a novice, so at this point any sort of helpful guidance is appreciated. In fact, the feedback has already been helpful in that I've learned that the problem could be something other than a bent prop or shaft. The fact that it could be a bearing, or engine alignment are things I didn't know before posting. So in that sense I find the feedback beneficial even if it doesn't tell me that my specific issue is X or Y.
That comment is directed at those that are so sure it is only one thing.

The fact that a bunch of people, some with a lot of experience have suggested several things only makes it more curious how a 10 second video could be so conclusive to others.
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Old 06-28-2017, 06:55 PM   #20
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There is runout visible. Put dial indicator on shaft about a foot aft of coupling and roll it by hand. If zero or close, then likely prop. If significant, like over 0.020", then loosen coupling bolts one turn each and repeat. If runout decreases significantly, there is runout in either shaft coupling flange or tranny flange. If runout still there, shaft likely bent.

Above is an easy check that will narrow the list of possibilities. Can be done in under an hour.
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