Yamaha 5hp outboard slipping

[jbm1967]

Hi, I have a Yamaha 5BS that has suddenly started slipping. It revs fine but the prop turns very slow. This happens in forward and reverse. Best described as like a slipped clutch. The prop is the shear pin type so it’s not a spun hub and the shear pin is fine. It engages easily in gears. Any ideas what the problem could be would be greatly appreciated. Thanks

 

[oldharry]

Even with a shear pin drive many props have a bonded rubber drive cushioning the prop. If the bonding fails it does what you describe. Otherwise it could be stripped splines on the drive what for in the gearbox. My money goes on the prop.

 

[Monique]

You need a new prop. Rubber coupling has become loose.... or you could pin it through the prop housing and ignore the issue until you hit something hard and destroy the gearbox.

 

[jbm1967]

Even with a shear pin drive many props have a bonded rubber drive cushioning the prop. If the bonding fails it does what you describe. Otherwise it could be stripped splines on the drive what for in the gearbox. My money goes on the prop.

Ok, thanks. I thought it was one or the other. Let’s hope it’s that then.

 

[VicS]

Ok, thanks. I thought it was one or the other. Let’s hope it’s that then.

Mark the prop in line with the head of the cotter pin (split pin) that secures the prop retaining "nut" with a waterproof marker

Give the engine a run until the drive slips.

Re-examine the mark If it is no longer in line with the head of the split pin it confirms the spun hub.

 

[jbm1967]

You need a new prop. Rubber coupling has become loose.... or you could pin it through the prop housing and ignore the issue until you hit something hard and destroy the gearbox.

Ok wasn’t aware you had shear pins and rubber couplings together (new to outboards). I take your point but would it not destroy the shear pin if I pinned it?

 

[jbm1967]

Mark the prop in line with the head of the cotter pin (split pin) that secures the prop retaining "nut" with a waterproof marker

Give the engine a run until the drive slips.

Re-examine the mark If it is no longer in line with the head of the split pin it confirms the spun hub.

Sounds like a plan. Will try that. Cheers

 

[VicS]

Ok wasn’t aware you had shear pins and rubber couplings together (new to outboards). I take your point but would it not destroy the shear pin if I pinned it?

Some outboard props have a rubber bonded hub that is not designed to slip .... they have shear pins as protection ........ I guess that describes yours

Others have a rubber hub that is designed to slip ... but no shear pin
(Maybe some have both ???)

ITYWF that more recent 5 hp Yamahas do not have shear pins

See waht I said about confirming the spun hub in #5

 

[jbm1967]

Was definitely the rubber hub. See pic if it attaches. Thanks to all

 

[Boathook]

You can get them rebushed. Steel Developments in SW London do it (I suspect that there are others) but do check on the price of a replacement prop first.

 

[Triassic]

I had exactly the same issue and yes, it was the rubber bushing inside the prop that had failed. I bought a new prop but couldn't get one exactly the same (high thrust). I've since pushed the remains of the bush out of the old prop, cleaned everything as best I could and rebonded it using an epoxy type glue. Certainly feels well stuck, waiting on an opportunity to test it properly!

 

[anoccasionalyachtsman]

You can buy two part polyurethane 'rubber' which is used by diyers for car suspension bushes (among other things). I'd be very tempted to give that a go.