Prop Slip on a 2 stroke 5hp Yamaha OB

[BigART]

When attempting higher power settings on my 2008 vintage 2 stroke 5hp Yamaha outboard, it has started racing with no apparent increase in thrust, I am suspecting that the prop is slipping on its rubber bush as there does not appear to be a shear pin. I have had the odd plastic bag round the prop so maybe that has caused it.

Has anyone alse had this and had a solution - other than a new prop. I am currently in an out of the way location where replacements are not available. I am thinking of drilling and tapping a couple of 5mm holes and putting a pair of 'Duralaced' SS bolts in as a temporary solution. Any other ideas for a fix?

Angus

 

[Gypsy]

Your diagnosis is most likely spot on. I have a 3HP Malta which had the same problem after I clipped a rock. I have read of others putting self taps into the rubber bush. I dug out a bit of the rubber and put in some araldite glue which kept mine going for a few months. It depends upon how much 'grip' is left.

 

[Pagetslady]

I had this problem on my Malta I cured it by drilling a hole in the Aluminum prop and screwing a selftapper into the rubber, make sure it doesnt go through.
Mike

 

[simonfraser]

might vibrate less if you put two screws in on oposing sides ?

 

[BigART]

Yamaha 5hp prop slip

Thanks folks, right, that's it then, out with the cordless drill. I had considered the asymmetric aspect, so two bolts/self tappers. What was wrong with shear pins I wonder. Probably they couldn't charge the outrageous price that they can for a new prop.

Fair winds

Angus

 

[boguing]

You are sure that it's not cavitating?

What does it do if you raise the revs slowly, giving the boat time to accelerate?

 

[BigART]

Cavitating?

I am pretty sure it is not that. The prop is normally fairly deep but it sometimes has cavitated in choppy water. This feels different occuring below planing speed at more that about half power.

A

 

[VicS]

It usually quite simple to prove whether or not the prop hub is spun.

Mark a line across the end of the prop shaft and the prop hub. Go for a spin. Make sure you go to the point where you notice the symptoms.

If the marks on the prop and the end of the shaft no longer line up it is spun!

The other thing that can happen is that the dog clutch becomes worn (usually as a result of gentle gear engagements instead of a quick snap action). When that happens it can jump out of gear. You know when that has happened because the gear shifter moves to neutral and you can put it back into gear again.
A spun hub on the other hand recovers drive itself when you throttle down.


BTW dont confuse cavitation, which can occur even when the prop is deeply immersed, with ventilation which occurs when the prop is insufficiently immersed and draws air down into it.

 

[BigART]

Prop Spin

Thanks Vic, I like that suggestion. I have reinstalled the prop and marked it up for a slip test. I don't think there is a clutch problem as there seems to be a good positive 'clunk' on engagement.

Angus

 

[VicS]

Thanks Vic, I like that suggestion. I have reinstalled the prop and marked it up for a slip test. I don't think there is a clutch problem as there seems to be a good positive 'clunk' on engagement.

Angus

I mention the clutch only because people often believe they are doing right by engaging it gently.
Its a dog clutch, not a friction clutch as in a car for example, and gentle engagement over the years can round of the corners of the clutch dog (and the gears) to the point that under load they pop out of gear again into neutral..

Correct procedure is to reduce the engine revs and engage with one quick snap action. It seems brutal ( it is if the engine is running too fast!) but in the long term is better for the clutch.

Little doubt that you will find you have a spun hub!

 

[dualin]

prop slip

Hi this is a definent rubber bush problem i have had it and it was on an older Yamaha outboard and somone before me had "bodged" the job with screws through the sides of the prop into the rubber which ended up with more corrosien around the rubber bush which will ultimley end up knackering the prop! the bush is there for a reason and that is to dampen any imbalences out of the drive train also to cussion the snatch from astern to ahead without breaking the shear pin ,honistly it does not matter how carfull you do it the pin is a weak link for a reason. phone castle marine in north wales and for £40 its job done with a warrenty and they text you when they have put it in the post first class service.