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Old 30 August 2013, 15:21   #1
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Nut's Got Bigger

Chaps,Two weeks of daily buzzing off Cornwall. Pulled the SR onto the trailer. Flushed and ran dry.
Noticed play on prop, along the shaft, of about 1 cm.
the castellated brass nut is still there held by the split pin.
But the prop moves along the shaft by about 1 cm.
Initial thoughts were that a washer had disinertgrated.
While starting to remove split pin realised the nut was moving along the shaft too. Thought it had cross threaded but threads appeared sharp.
It seems to have expanded and simply slides over the male shaft thread.
If a washer had gone then threads would be unaffected.
Very puzzling esp as the prop has been held on by a split pin stopping a suddenly too large brass castellated nut from dropping off.
Eh?
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Old 30 August 2013, 16:37   #2
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Unusual for the castellated nut to be damaged like that. Any pictures?

What's the propeller bush like? There should be a thrust washer, then the propeller, then another washer and finally the castellated nut and split pin.
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Old 30 August 2013, 16:44   #3
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Originally Posted by spartacus View Post
Unusual for the castellated nut to be damaged like that. Any pictures?

What's the propeller bush like? There should be a thrust washer, then the propeller, then another washer and finally the castellated nut and split pin.
I reckon the "another washer" has disintergrated. But how the hell did the nut get bigger? I know a stripped thread, this is as if the nut had a 20% enlarge ray zapped on it. Threads are sharp.
Sneaking suspicion is that it could have been replaced by somebody needing right size. However, the split pin was replaced.
Washer is missing hence the play. Understood, could have broken off. But why would the nut no longer fit the thread?
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Old 30 August 2013, 16:46   #4
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The nut could have split
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Old 30 August 2013, 16:50   #5
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If the prop has play it will hammer against the nut while underway. Could this have caused the damaged nut?
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Old 30 August 2013, 16:51   #6
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Sneaking suspicion is that it could have been replaced by somebody needing right size.
“Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”
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Old 30 August 2013, 16:52   #7
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Nut is still there. Held by the split pin. It's just that all of a sudden it is too large to tighten against the prop. The thread is there, as it is on the shaft. It's just that the nut has grown to be able to slide over ther shaft's threads.
If I were to take a picture, all you would see is an oversized castellated nut held by a split pin.
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Old 30 August 2013, 17:26   #8
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Are you sure you've not imagined the whole thing?

You wouldn't be the first to experience the feeling you have bigger nuts than you really do when piloting a Searider around for a few days.

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Old 30 August 2013, 21:09   #9
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Quote:
Originally Posted by spartacus View Post
Unusual for the castellated nut to be damaged like that. Any pictures?

What's the propeller bush like? There should be a thrust washer, then the propeller, then another washer and finally the castellated nut and split pin.
Possibly a spacer in there as well, depending on motor and prop combo.

But yeah; I'd believe the stolen/replaced scenario.

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Old 31 August 2013, 03:08   #10
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Quote:
Originally Posted by willk View Post
“Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”
I can't imagine how a nut could grow without damaging the threads.

In the absence of a thrust washer, fretting corrosion could have damaged the threads and made the nut ID bigger in the way you describe but then the threads would have been chewed.

I can't even imagine how the washer would disappear other than by theft. But someone would steal a thrust washer and put the split pin back? To say nothing of the prop ...

Are you sure the prop you now have is "yours"?
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