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Old 08-05-2015, 20:53   #1
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Shaft flex?

Hi guys

So a issue I have been having with my new to me boat is a metallic knock coming from the shaft behind the stern tube. It's not hugely loud but it's there. The engine mounts were cactus and the prob was covered in barnacles so I have rebuilt mounts and cleaned prop and I have aligned it in the water about 5 times now but I still can't totally get rid of it. Because there is a pss shaft seal I can't get the shaft exactly centred but when playing around with it today I noticed that it has a fair amount of movement up and down but next to nothing side ways and when I slightly shake it I hear the metallic knock. So even a small amount of Shake would make that noise. It is a 1.5 inch shaft and I would say about 2 meters long with 1 meter between coupling and stern tube and 1 meter to the prop. There is no bearing in the stern tube apart from the cutlass bearing and I get no movement when I shake the prop. So, is it possible I have a bit of slop in the shaft . It is also noticeable mainly when I run up over 1500rpm. The boat max is 2500rpm


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Old 08-05-2015, 21:07   #2
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Re: Shaft flex?

Take the bolts out of your coupling at the transmission and slide the shaft back a bit. It should be easier to find your problem.


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Old 08-05-2015, 21:21   #3
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Re: Shaft flex?

With a shaft that short in relation to its diameter there are two items I would check.
1) the cutless bearing in the strut
2) like above, seperate the couplers at the tranny and check the couples on the tranny and the shaft for looseness.

And one other possibility, if the shaft is too close to one side of the stern tube it could be hitting the tube.
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Old 08-05-2015, 21:43   #4
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Re: Shaft flex?

Quote:
Originally Posted by delmarrey View Post
With a shaft that short in relation to its diameter there are two items I would check.

1) the cutless bearing in the strut

2) like above, seperate the couplers at the tranny and check the couples on the tranny and the shaft for looseness.



And one other possibility, if the shaft is too close to one side of the stern tube it could be hitting the tube.

Actually one other thing I did notice is that when I turn the shaft by hand I notice what feels like something loose but I have traced that back to some slack in the transmission. When I rotata the shaft even a small amount I hear a knock when it stops but it's coming from inside the transmission. Is that a normal sound? Hard to explain. I will disconnect again and see if there is any movement at the coupler at the transmission side.


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Old 08-05-2015, 21:48   #5
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Re: Shaft flex?

If the shaft had been out of alignment for a period of time, it may have damaged the tranny output bearing. If the rear tranny seal is leaking, that would be a good sign.
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Old 08-05-2015, 21:53   #6
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Re: Shaft flex?

True. I think it was out for a while as the engine mounts were totally chewed out. Having said that the previous owner only took it out twice in the year he had it but who knows prior to that. No leaks anywhere and doesn't appear to have any problems


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