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Prop loose on shaft?

NormanB

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Engine is very poorly and out of the boat.

Cleaning out the empty space today I casually twirled the coupling. Seems like there is a couple of degrees play in both directions before the prop turns.

Is the prop loose on the shaft, and if so why? Don't want to add a Cascais liftout to the cost of fixing the engine. (Plan is to have a wee sail around the Algarve then lift out at Bruce's if there is space, so will fix wonky props etc then, but will it fall off before then?)

- W
It sounds more like excessive play in the coupling/shaft connection and nowt to do with the prop.
 

webcraft

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In a fraction of the time its taken to debate this on here, someone could have been in the water and checked it out. Water cold, no wetsuit onboard, Decathlon. You may need a rope round keel to pull yourself down. 2 minutes in the water and all will be revealed. Then you can debate the solutions.
Hmmm... Decathlon Cascais have a 1.5mm shorty for 17 euros, might encourage me...

- W
 

NormanB

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Good suggestion. Will check that out. What causes shaft/coupling play?

- W
Well it could have been caused well in the past by under tightened bolts, which would allow the coupling to rock on the key and increase clearance between key and keyway over time in service. At the same time the bolt holes in the coupling wearing to a slight oval shape, or the bolts neck slightly in way of the load line. All will be revealed if yours strip it down and give it an optical bollicking, or better measure it on the bench - key to keyway,, and all bolts for wear and diameters with respect to their respective bolt holes. Pretty straightforward to rectify for any basically equipped workshop.
 
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Norman_E

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Do you have one of these tab washers? Propeller nut locking tab washers::

If you do not I suggest you get one fitted. If you do then the dangerous possibility is that the shaft key has sheared and the prop is only being stopped from complete rotation by the tab washer, whilch may spin the nuts off if you run the engine. A badly fitted key, either loose, or too tall so that the prop does not bed down properly on the taper is the common cause of propellers coming loose.
 

RichardS

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If the nuts have not moved and the prop was tight on the shaft before, what can have moved or worn to cause this?
- W
If the prop really was tight on the shaft, then I agree with you that it would not have changed. I'm suggesting that it was tight until the lock nuts were done up and then it was backed-off slightly. There then might have been enough play to work backwards and forwards a little in normal use until the surfaces wore a little more sufficiently such that you can feel it through the shaft.

Richard
 

greeny

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Hmmm... Decathlon Cascais have a 1.5mm shorty for 17 euros, might encourage me...

- W
But on reading the rest of this thread it seems you've not yet determined that the movement you're feeling is not coupling to shaft movement inside the boat.
 

webcraft

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But on reading the rest of this thread it seems you've not yet determined that the movement you're feeling is not coupling to shaft movement inside the boat.
I'm in there again just now, and I can't tell. I would need to be able to hold the shaft still; how to clamp it without markng/damaging it?

- W
 

greeny

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I'm in there again just now, and I can't tell. I would need to be able to hold the shaft still; how to clamp it without markng/damaging it?

- W
Maybe I'm not seeing in my mind's eye what you've got there. Earlier you said you could feel the movement just by casually twirling the coupling. So just holding the shaft with your hand whilst moving the coupling should be enough to feel any movement between the two. If not possible then do what Northup said with the mole grips and a rag.
 

webcraft

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OK, it is definitely not the connection between the coupling and the shaft, which really only leaves the prop rocking on the key...

Question is, if that Is what it is, how long until it shears?

- W
 

jamie N

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Question is, if that Is what it is, how long until it shears?

- W
This is where you might award yourself $64,000 for the best question of the night!
You won't know until you've access, I'd say.
But on the positive side, you only became aware of the 'issue' when you very specifically rotated the shaft; there haven't been any symptoms apparent otherwise.
As said before, only use it if you must perhaps until you can get it seen to is a way forward.
 

BlowingOldBoots

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If your prop shaft has slipped back by small amount and the weight of the gearbox is pulling down the shaft, the tip of the blade could be hitting off the top of the rudder cut out. This is based on the image you posted.

My own experience of removing a coupling in the water resulted in the shaft slipping backwards rather fast and striking the skeg, which surprised me, as I assumed it would be clamped reasonably well by stuffing box and cutless bearing. On hindsight, of course not!

Double nutting in rotating things is an unreliable method of securing the fastening.
 

penberth3

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I'm in there again just now, and I can't tell. I would need to be able to hold the shaft still; how to clamp it without markng/damaging it?

- W
Try putting a finger tip lightly across the two parts. Easy to feel any relative movement. Shaft doesn't need to be clamped, but it might help.

Edit - just noticed, you've already checked it!
 

greeny

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If your prop shaft has slipped back by small amount and the weight of the gearbox is pulling down the shaft, the tip of the blade could be hitting off the top of the rudder cut out. This is based on the image you posted.

My own experience of removing a coupling in the water resulted in the shaft slipping backwards rather fast and striking the skeg, which surprised me, as I assumed it would be clamped reasonably well by stuffing box and cutless bearing. On hindsight, of course not!

Double nutting in rotating things is an unreliable method of securing the fastening.
Sounds like the answer to me. Or the shaft has gone back even further and the prop tips are hitting the rear of the aperture.
 

webcraft

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Sounds like the answer to me. Or the shaft has gone back even further and the prop tips are hitting the rear of the aperture.
I can slide the shaft back until the prop hits the edge of the aperture.. Of course.

But what I am describing occurs with the shaft pulled forward and is nothing to do with the prop touching anything.

I have borrowed a shortie wetsuit off a new arrival on a Vancouver 32, and will have a look tomorrow.

In other news, I finished cleaning the engine bilge today and Danbolined it.

- W
 
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