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Old 22-05-2014, 08:41 PM   #1
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Tighting Props and loose nuts

Was down in Teignmouth last week and popped in to have a look around the lifeboat station. In the station they have a large rib with twin 115 or around that size Merc Outboards. I was walking round noticed shiny bits and wear marks on the prop washers on both engines. The prop nuts although has split pins in were wobbly with the fingers loose as were the washers completly loose so you cold turn the washers with your fingers.

I inquired as to why and was told that was how they are supposed to be and it stops the shafts shearing if they hit something submerged.

Has anyone heard of this before and how tight should pro nuts be???
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Old 27-06-2014, 02:09 AM   #2
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Prop nut torque

Mmm, never heard of that one. Usually it's set to 80nm on the castle nut, this will be lower on smaller outboards say under 30hp 10-20nm and up to 135nm for props with a bush between the thrust washer and prop. I normally set to 80nm and re check after a few runs as the thrust washer seats further onto the shaft
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Old 27-06-2014, 07:58 AM   #3
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Can't see how it would stop the shafts shearing unless it puts less torque on the hub. But mercs don't usually have split puns or castle nuts so its sounds like its something they've done! There's probably some method to the madness!

On a side note, whatever I torqued the prop nut to on my sportcat it was always loose after a run.
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Old 27-06-2014, 10:30 AM   #4
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that tells me the bush is not seated on the thrust washer and i have seen flo torque failure due to this
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Old 07-08-2014, 12:52 PM   #5
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Hi Im a technician for the rnli the reason behind it is for a easy prop change at sea. If prop gets damaged whils out on a shout ;-)
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Old 13-08-2014, 08:30 AM   #6
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I used to use a Terry pin (bit like a large nappy pin) the same diameter as the split pin would be...that and a floating prop nut wrench would still give you a quick prop change at sea....did it several times when prop testing without the need to keep going back on the trailer.
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