Free Spining prop yamaha 50hp 86 model

[portabletelly]

OK Where do I start: (I am a bit of a do it yourself novice when it comes to boat motors)

Background;
The other day I was out on my 16ft half cabin 50hp yamaha boat on a 15 km boat ride to an island of the South East QLD coast of Australia. About 10 km into the trip the motor started revving excessivley and the boat speed dropped dramatically. I brought the boat to a halt and slowly began to drive away again but as soon as the boat speed got to about walking speed the motor seemed to over rev but would not turn the propella. However if I put the boat in revers the motor seemed to rev normally without the prop slipping.

What I have done:
Because my impella was due for a change as well (lack of water pressure) I pulled the bottom half of the motor apart. Which is a 1986 yamaha 50hp motor.
I originally thought that the lever that changes gears might have been slipping out of gear. So I lossend the bolt to lengthen the cable and when the boat is in gear i can turn the prop which seems to be turning the whole drive shaft (should this happen it doesnt happen in Reverse.

My second guess was that someone told me the bushes in the prop may be gone but when i turn the prop it turns the whole drive shaft. So that rulled out my second guess that it was the bushes in the prop.

Does anyone have any ideas on what else it could be or what I could do to find out exactly what would be making the motor rev but the prop not turning accordingly.

cheers

portabletelly


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[BarryH]

The cush drive bush sounds fav. You won't make it slip by hand. You need to haver it done by a prop speacialist. Don't know of any near you seeing as I'm a few thousand miles away!

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[adarcy]

Agreed Barry

the bush in the prop is slipping like a weak clutch when the engine power increases.
Testing by hand does nothing useful. If he REALLY wants to, he can drive it hard and slipping for a long time then sudden stop tip it up and see/feel if the bush is hot + sticky

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[mainshiptom]

If you can get a new prop or second hand and test ?

Tom

ps some props are pushed on an insert to make the process cheper !

Your insert is dlipping under the strain !

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[jfm]

Sounds like the rubber bush. To test this, mark the splined hub and the prop outer casting with a marker pen, paint or a scriber. Then run engine till it slips. Then re-examine. If the marks have moved relative to one another, the bush must be slipping

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[Dave1258]

Are all outboard props designed that way or is it a Yammy thing?

<hr width=100% size=1> A man should have two things in life, a boat and a wife willing to let him have one.

 

[BarryH]

A fair few have them, mercs/mariners hondas. Good rule of thumb, if its got thru hub exhaust its got a bush. Or if it has no shear pin fitted. Its just the weak link to save the gearbox if the prop hits something solid that'll stop it turning.
Had mine re bushed a few years ago. We hit a submerged tree trunk on the Thames. Come off the plane pretty quick sharp'ish!

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[portabletelly]

Thanks all for your comments I will take the prop down and get recompressed with new bushes. They tell me this costs aout $70 AU. Can someone answer my question about turning the prop by hand.

If the boat is in gear should you be able to turn the prop by hand it seems to make a clicking sound when I do this.

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[BarryH]

Yus thats normal. If you have it in gear "ahead" you shouldn't be able to turn in backwards. If you have it in "astern" you shouldn't be able to turn it forwards. Which way it turns in which direction depends on what prop you have. More than likely you'll have a right handed prop, turns clockwise to push you forward......confused......I am!!!

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[jfm]

Yup all correct. It turns one way with a click sound, not the other (well, it would, but you'd be cranking the whole engine...). It's like a bycycle wheel, one direction is driving, the other is over run freewheeling

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